1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
//! An implementation of asynchronous process management for Tokio.
//!
//! This module provides a [`Command`] struct that imitates the interface of the
//! [`std::process::Command`] type in the standard library, but provides asynchronous versions of
//! functions that create processes. These functions (`spawn`, `status`, `output` and their
//! variants) return "future aware" types that interoperate with Tokio. The asynchronous process
//! support is provided through signal handling on Unix and system APIs on Windows.
//!
//! [`std::process::Command`]: std::process::Command
//!
//! # Examples
//!
//! Here's an example program which will spawn `echo hello world` and then wait
//! for it complete.
//!
//! ```no_run
//! use tokio::process::Command;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     // The usage is similar as with the standard library's `Command` type
//!     let mut child = Command::new("echo")
//!         .arg("hello")
//!         .arg("world")
//!         .spawn()
//!         .expect("failed to spawn");
//!
//!     // Await until the command completes
//!     let status = child.wait().await?;
//!     println!("the command exited with: {}", status);
//!     Ok(())
//! }
//! ```
//!
//! Next, let's take a look at an example where we not only spawn `echo hello
//! world` but we also capture its output.
//!
//! ```no_run
//! use tokio::process::Command;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     // Like above, but use `output` which returns a future instead of
//!     // immediately returning the `Child`.
//!     let output = Command::new("echo").arg("hello").arg("world")
//!                         .output();
//!
//!     let output = output.await?;
//!
//!     assert!(output.status.success());
//!     assert_eq!(output.stdout, b"hello world\n");
//!     Ok(())
//! }
//! ```
//!
//! We can also read input line by line.
//!
//! ```no_run
//! use tokio::io::{BufReader, AsyncBufReadExt};
//! use tokio::process::Command;
//!
//! use std::process::Stdio;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let mut cmd = Command::new("cat");
//!
//!     // Specify that we want the command's standard output piped back to us.
//!     // By default, standard input/output/error will be inherited from the
//!     // current process (for example, this means that standard input will
//!     // come from the keyboard and standard output/error will go directly to
//!     // the terminal if this process is invoked from the command line).
//!     cmd.stdout(Stdio::piped());
//!
//!     let mut child = cmd.spawn()
//!         .expect("failed to spawn command");
//!
//!     let stdout = child.stdout.take()
//!         .expect("child did not have a handle to stdout");
//!
//!     let mut reader = BufReader::new(stdout).lines();
//!
//!     // Ensure the child process is spawned in the runtime so it can
//!     // make progress on its own while we await for any output.
//!     tokio::spawn(async move {
//!         let status = child.wait().await
//!             .expect("child process encountered an error");
//!
//!         println!("child status was: {}", status);
//!     });
//!
//!     while let Some(line) = reader.next_line().await? {
//!         println!("Line: {}", line);
//!     }
//!
//!     Ok(())
//! }
//! ```
//!
//! Here is another example using `sort` writing into the child process
//! standard input, capturing the output of the sorted text.
//!
//! ```no_run
//! use tokio::io::AsyncWriteExt;
//! use tokio::process::Command;
//!
//! use std::process::Stdio;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let mut cmd = Command::new("sort");
//!
//!     // Specifying that we want pipe both the output and the input.
//!     // Similarily to capturing the output, by configuring the pipe
//!     // to stdin it can now be used as an asynchronous writer.
//!     cmd.stdout(Stdio::piped());
//!     cmd.stdin(Stdio::piped());
//!
//!     let mut child = cmd.spawn().expect("failed to spawn command");
//!
//!     // These are the animals we want to sort
//!     let animals: &[&str] = &["dog", "bird", "frog", "cat", "fish"];
//!
//!     let mut stdin = child
//!         .stdin
//!         .take()
//!         .expect("child did not have a handle to stdin");
//!
//!     // Write our animals to the child process
//!     // Note that the behavior of `sort` is to buffer _all input_ before writing any output.
//!     // In the general sense, it is recommended to write to the child in a separate task as
//!     // awaiting its exit (or output) to avoid deadlocks (for example, the child tries to write
//!     // some output but gets stuck waiting on the parent to read from it, meanwhile the parent
//!     // is stuck waiting to write its input completely before reading the output).
//!     stdin
//!         .write(animals.join("\n").as_bytes())
//!         .await
//!         .expect("could not write to stdin");
//!
//!     // We drop the handle here which signals EOF to the child process.
//!     // This tells the child process that it there is no more data on the pipe.
//!     drop(stdin);
//!
//!     let op = child.wait_with_output().await?;
//!
//!     // Results should come back in sorted order
//!     assert_eq!(op.stdout, "bird\ncat\ndog\nfish\nfrog\n".as_bytes());
//!
//!     Ok(())
//! }
//! ```
//!
//! With some coordination, we can also pipe the output of one command into
//! another.
//!
//! ```no_run
//! use tokio::join;
//! use tokio::process::Command;
//! use std::convert::TryInto;
//! use std::process::Stdio;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let mut echo = Command::new("echo")
//!         .arg("hello world!")
//!         .stdout(Stdio::piped())
//!         .spawn()
//!         .expect("failed to spawn echo");
//!
//!     let tr_stdin: Stdio = echo
//!         .stdout
//!         .take()
//!         .unwrap()
//!         .try_into()
//!         .expect("failed to convert to Stdio");
//!
//!     let tr = Command::new("tr")
//!         .arg("a-z")
//!         .arg("A-Z")
//!         .stdin(tr_stdin)
//!         .stdout(Stdio::piped())
//!         .spawn()
//!         .expect("failed to spawn tr");
//!
//!     let (echo_result, tr_output) = join!(echo.wait(), tr.wait_with_output());
//!
//!     assert!(echo_result.unwrap().success());
//!
//!     let tr_output = tr_output.expect("failed to await tr");
//!     assert!(tr_output.status.success());
//!
//!     assert_eq!(tr_output.stdout, b"HELLO WORLD!\n");
//!
//!     Ok(())
//! }
//! ```
//!
//! # Caveats
//!
//! ## Dropping/Cancellation
//!
//! Similar to the behavior to the standard library, and unlike the futures
//! paradigm of dropping-implies-cancellation, a spawned process will, by
//! default, continue to execute even after the `Child` handle has been dropped.
//!
//! The [`Command::kill_on_drop`] method can be used to modify this behavior
//! and kill the child process if the `Child` wrapper is dropped before it
//! has exited.
//!
//! ## Unix Processes
//!
//! On Unix platforms processes must be "reaped" by their parent process after
//! they have exited in order to release all OS resources. A child process which
//! has exited, but has not yet been reaped by its parent is considered a "zombie"
//! process. Such processes continue to count against limits imposed by the system,
//! and having too many zombie processes present can prevent additional processes
//! from being spawned.
//!
//! The tokio runtime will, on a best-effort basis, attempt to reap and clean up
//! any process which it has spawned. No additional guarantees are made with regards
//! how quickly or how often this procedure will take place.
//!
//! It is recommended to avoid dropping a [`Child`] process handle before it has been
//! fully `await`ed if stricter cleanup guarantees are required.
//!
//! [`Command`]: crate::process::Command
//! [`Command::kill_on_drop`]: crate::process::Command::kill_on_drop
//! [`Child`]: crate::process::Child

#[path = "unix/mod.rs"]
#[cfg(unix)]
mod imp;

#[cfg(unix)]
pub(crate) mod unix {
    pub(crate) use super::imp::*;
}

#[path = "windows.rs"]
#[cfg(windows)]
mod imp;

mod kill;

use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
use crate::process::kill::Kill;

use std::convert::TryInto;
use std::ffi::OsStr;
use std::future::Future;
use std::io;
#[cfg(unix)]
use std::os::unix::process::CommandExt;
#[cfg(windows)]
use std::os::windows::io::{AsRawHandle, RawHandle};
#[cfg(windows)]
use std::os::windows::process::CommandExt;
use std::path::Path;
use std::pin::Pin;
use std::process::{Command as StdCommand, ExitStatus, Output, Stdio};
use std::task::Context;
use std::task::Poll;

/// This structure mimics the API of [`std::process::Command`] found in the standard library, but
/// replaces functions that create a process with an asynchronous variant. The main provided
/// asynchronous functions are [spawn](Command::spawn), [status](Command::status), and
/// [output](Command::output).
///
/// `Command` uses asynchronous versions of some `std` types (for example [`Child`]).
///
/// [`std::process::Command`]: std::process::Command
/// [`Child`]: struct@Child
#[derive(Debug)]
pub struct Command {
    std: StdCommand,
    kill_on_drop: bool,
}

pub(crate) struct SpawnedChild {
    child: imp::Child,
    stdin: Option<imp::ChildStdio>,
    stdout: Option<imp::ChildStdio>,
    stderr: Option<imp::ChildStdio>,
}

impl Command {
    /// Constructs a new `Command` for launching the program at
    /// path `program`, with the following default configuration:
    ///
    /// * No arguments to the program
    /// * Inherit the current process's environment
    /// * Inherit the current process's working directory
    /// * Inherit stdin/stdout/stderr for `spawn` or `status`, but create pipes for `output`
    ///
    /// Builder methods are provided to change these defaults and
    /// otherwise configure the process.
    ///
    /// If `program` is not an absolute path, the `PATH` will be searched in
    /// an OS-defined way.
    ///
    /// The search path to be used may be controlled by setting the
    /// `PATH` environment variable on the Command,
    /// but this has some implementation limitations on Windows
    /// (see issue [rust-lang/rust#37519]).
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    /// let command = Command::new("sh");
    /// ```
    ///
    /// [rust-lang/rust#37519]: https://github.com/rust-lang/rust/issues/37519
    pub fn new<S: AsRef<OsStr>>(program: S) -> Command {
        Self::from(StdCommand::new(program))
    }

    /// Cheaply convert to a `&std::process::Command` for places where the type from the standard
    /// library is expected.
    pub fn as_std(&self) -> &StdCommand {
        &self.std
    }

    /// Adds an argument to pass to the program.
    ///
    /// Only one argument can be passed per use. So instead of:
    ///
    /// ```no_run
    /// tokio::process::Command::new("sh")
    ///   .arg("-C /path/to/repo");
    /// ```
    ///
    /// usage would be:
    ///
    /// ```no_run
    /// tokio::process::Command::new("sh")
    ///   .arg("-C")
    ///   .arg("/path/to/repo");
    /// ```
    ///
    /// To pass multiple arguments see [`args`].
    ///
    /// [`args`]: method@Self::args
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .arg("-l")
    ///         .arg("-a");
    /// ```
    pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command {
        self.std.arg(arg);
        self
    }

    /// Adds multiple arguments to pass to the program.
    ///
    /// To pass a single argument see [`arg`].
    ///
    /// [`arg`]: method@Self::arg
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .args(&["-l", "-a"]);
    /// ```
    pub fn args<I, S>(&mut self, args: I) -> &mut Command
    where
        I: IntoIterator<Item = S>,
        S: AsRef<OsStr>,
    {
        self.std.args(args);
        self
    }

    /// Inserts or updates an environment variable mapping.
    ///
    /// Note that environment variable names are case-insensitive (but case-preserving) on Windows,
    /// and case-sensitive on all other platforms.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .env("PATH", "/bin");
    /// ```
    pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Command
    where
        K: AsRef<OsStr>,
        V: AsRef<OsStr>,
    {
        self.std.env(key, val);
        self
    }

    /// Adds or updates multiple environment variable mappings.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    /// use std::process::{Stdio};
    /// use std::env;
    /// use std::collections::HashMap;
    ///
    /// let filtered_env : HashMap<String, String> =
    ///     env::vars().filter(|&(ref k, _)|
    ///         k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH"
    ///     ).collect();
    ///
    /// let command = Command::new("printenv")
    ///         .stdin(Stdio::null())
    ///         .stdout(Stdio::inherit())
    ///         .env_clear()
    ///         .envs(&filtered_env);
    /// ```
    pub fn envs<I, K, V>(&mut self, vars: I) -> &mut Command
    where
        I: IntoIterator<Item = (K, V)>,
        K: AsRef<OsStr>,
        V: AsRef<OsStr>,
    {
        self.std.envs(vars);
        self
    }

    /// Removes an environment variable mapping.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .env_remove("PATH");
    /// ```
    pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command {
        self.std.env_remove(key);
        self
    }

    /// Clears the entire environment map for the child process.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .env_clear();
    /// ```
    pub fn env_clear(&mut self) -> &mut Command {
        self.std.env_clear();
        self
    }

    /// Sets the working directory for the child process.
    ///
    /// # Platform-specific behavior
    ///
    /// If the program path is relative (e.g., `"./script.sh"`), it's ambiguous
    /// whether it should be interpreted relative to the parent's working
    /// directory or relative to `current_dir`. The behavior in this case is
    /// platform specific and unstable, and it's recommended to use
    /// [`canonicalize`] to get an absolute program path instead.
    ///
    /// [`canonicalize`]: crate::fs::canonicalize()
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .current_dir("/bin");
    /// ```
    pub fn current_dir<P: AsRef<Path>>(&mut self, dir: P) -> &mut Command {
        self.std.current_dir(dir);
        self
    }

    /// Sets configuration for the child process's standard input (stdin) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`piped`] when used with `output`.
    ///
    /// [`inherit`]: std::process::Stdio::inherit
    /// [`piped`]: std::process::Stdio::piped
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use std::process::{Stdio};
    /// use tokio::process::Command;
    ///
    /// let command = Command::new("ls")
    ///         .stdin(Stdio::null());
    /// ```
    pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
        self.std.stdin(cfg);
        self
    }

    /// Sets configuration for the child process's standard output (stdout) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`piped`] when used with `output`.
    ///
    /// [`inherit`]: std::process::Stdio::inherit
    /// [`piped`]: std::process::Stdio::piped
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    /// use std::process::Stdio;
    ///
    /// let command = Command::new("ls")
    ///         .stdout(Stdio::null());
    /// ```
    pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
        self.std.stdout(cfg);
        self
    }

    /// Sets configuration for the child process's standard error (stderr) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`piped`] when used with `output`.
    ///
    /// [`inherit`]: std::process::Stdio::inherit
    /// [`piped`]: std::process::Stdio::piped
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    /// use std::process::{Stdio};
    ///
    /// let command = Command::new("ls")
    ///         .stderr(Stdio::null());
    /// ```
    pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
        self.std.stderr(cfg);
        self
    }

    /// Controls whether a `kill` operation should be invoked on a spawned child
    /// process when its corresponding `Child` handle is dropped.
    ///
    /// By default, this value is assumed to be `false`, meaning the next spawned
    /// process will not be killed on drop, similar to the behavior of the standard
    /// library.
    ///
    /// # Caveats
    ///
    /// On Unix platforms processes must be "reaped" by their parent process after
    /// they have exited in order to release all OS resources. A child process which
    /// has exited, but has not yet been reaped by its parent is considered a "zombie"
    /// process. Such processes continue to count against limits imposed by the system,
    /// and having too many zombie processes present can prevent additional processes
    /// from being spawned.
    ///
    /// Although issuing a `kill` signal to the child process is a synchronous
    /// operation, the resulting zombie process cannot be `.await`ed inside of the
    /// destructor to avoid blocking other tasks. The tokio runtime will, on a
    /// best-effort basis, attempt to reap and clean up such processes in the
    /// background, but makes no additional guarantees are made with regards
    /// how quickly or how often this procedure will take place.
    ///
    /// If stronger guarantees are required, it is recommended to avoid dropping
    /// a [`Child`] handle where possible, and instead utilize `child.wait().await`
    /// or `child.kill().await` where possible.
    pub fn kill_on_drop(&mut self, kill_on_drop: bool) -> &mut Command {
        self.kill_on_drop = kill_on_drop;
        self
    }

    /// Sets the [process creation flags][1] to be passed to `CreateProcess`.
    ///
    /// These will always be ORed with `CREATE_UNICODE_ENVIRONMENT`.
    ///
    /// [1]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
    #[cfg(windows)]
    #[cfg_attr(docsrs, doc(cfg(windows)))]
    pub fn creation_flags(&mut self, flags: u32) -> &mut Command {
        self.std.creation_flags(flags);
        self
    }

    /// Sets the child process's user ID. This translates to a
    /// `setuid` call in the child process. Failure in the `setuid`
    /// call will cause the spawn to fail.
    #[cfg(unix)]
    #[cfg_attr(docsrs, doc(cfg(unix)))]
    pub fn uid(&mut self, id: u32) -> &mut Command {
        self.std.uid(id);
        self
    }

    /// Similar to `uid` but sets the group ID of the child process. This has
    /// the same semantics as the `uid` field.
    #[cfg(unix)]
    #[cfg_attr(docsrs, doc(cfg(unix)))]
    pub fn gid(&mut self, id: u32) -> &mut Command {
        self.std.gid(id);
        self
    }

    /// Sets executable argument.
    ///
    /// Set the first process argument, `argv[0]`, to something other than the
    /// default executable path.
    #[cfg(unix)]
    #[cfg_attr(docsrs, doc(cfg(unix)))]
    pub fn arg0<S>(&mut self, arg: S) -> &mut Command
    where
        S: AsRef<OsStr>,
    {
        self.std.arg0(arg);
        self
    }

    /// Schedules a closure to be run just before the `exec` function is
    /// invoked.
    ///
    /// The closure is allowed to return an I/O error whose OS error code will
    /// be communicated back to the parent and returned as an error from when
    /// the spawn was requested.
    ///
    /// Multiple closures can be registered and they will be called in order of
    /// their registration. If a closure returns `Err` then no further closures
    /// will be called and the spawn operation will immediately return with a
    /// failure.
    ///
    /// # Safety
    ///
    /// This closure will be run in the context of the child process after a
    /// `fork`. This primarily means that any modifications made to memory on
    /// behalf of this closure will **not** be visible to the parent process.
    /// This is often a very constrained environment where normal operations
    /// like `malloc` or acquiring a mutex are not guaranteed to work (due to
    /// other threads perhaps still running when the `fork` was run).
    ///
    /// This also means that all resources such as file descriptors and
    /// memory-mapped regions got duplicated. It is your responsibility to make
    /// sure that the closure does not violate library invariants by making
    /// invalid use of these duplicates.
    ///
    /// When this closure is run, aspects such as the stdio file descriptors and
    /// working directory have successfully been changed, so output to these
    /// locations may not appear where intended.
    #[cfg(unix)]
    #[cfg_attr(docsrs, doc(cfg(unix)))]
    pub unsafe fn pre_exec<F>(&mut self, f: F) -> &mut Command
    where
        F: FnMut() -> io::Result<()> + Send + Sync + 'static,
    {
        self.std.pre_exec(f);
        self
    }

    /// Executes the command as a child process, returning a handle to it.
    ///
    /// By default, stdin, stdout and stderr are inherited from the parent.
    ///
    /// This method will spawn the child process synchronously and return a
    /// handle to a future-aware child process. The `Child` returned implements
    /// `Future` itself to acquire the `ExitStatus` of the child, and otherwise
    /// the `Child` has methods to acquire handles to the stdin, stdout, and
    /// stderr streams.
    ///
    /// All I/O this child does will be associated with the current default
    /// event loop.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// async fn run_ls() -> std::process::ExitStatus {
    ///     Command::new("ls")
    ///         .spawn()
    ///         .expect("ls command failed to start")
    ///         .wait()
    ///         .await
    ///         .expect("ls command failed to run")
    /// }
    /// ```
    ///
    /// # Caveats
    ///
    /// ## Dropping/Cancellation
    ///
    /// Similar to the behavior to the standard library, and unlike the futures
    /// paradigm of dropping-implies-cancellation, a spawned process will, by
    /// default, continue to execute even after the `Child` handle has been dropped.
    ///
    /// The [`Command::kill_on_drop`] method can be used to modify this behavior
    /// and kill the child process if the `Child` wrapper is dropped before it
    /// has exited.
    ///
    /// ## Unix Processes
    ///
    /// On Unix platforms processes must be "reaped" by their parent process after
    /// they have exited in order to release all OS resources. A child process which
    /// has exited, but has not yet been reaped by its parent is considered a "zombie"
    /// process. Such processes continue to count against limits imposed by the system,
    /// and having too many zombie processes present can prevent additional processes
    /// from being spawned.
    ///
    /// The tokio runtime will, on a best-effort basis, attempt to reap and clean up
    /// any process which it has spawned. No additional guarantees are made with regards
    /// how quickly or how often this procedure will take place.
    ///
    /// It is recommended to avoid dropping a [`Child`] process handle before it has been
    /// fully `await`ed if stricter cleanup guarantees are required.
    ///
    /// [`Command`]: crate::process::Command
    /// [`Command::kill_on_drop`]: crate::process::Command::kill_on_drop
    /// [`Child`]: crate::process::Child
    ///
    /// # Errors
    ///
    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
    /// if the system process limit is reached (which includes other applications
    /// running on the system).
    pub fn spawn(&mut self) -> io::Result<Child> {
        imp::spawn_child(&mut self.std).map(|spawned_child| Child {
            child: FusedChild::Child(ChildDropGuard {
                inner: spawned_child.child,
                kill_on_drop: self.kill_on_drop,
            }),
            stdin: spawned_child.stdin.map(|inner| ChildStdin { inner }),
            stdout: spawned_child.stdout.map(|inner| ChildStdout { inner }),
            stderr: spawned_child.stderr.map(|inner| ChildStderr { inner }),
        })
    }

    /// Executes the command as a child process, waiting for it to finish and
    /// collecting its exit status.
    ///
    /// By default, stdin, stdout and stderr are inherited from the parent.
    /// If any input/output handles are set to a pipe then they will be immediately
    /// closed after the child is spawned.
    ///
    /// All I/O this child does will be associated with the current default
    /// event loop.
    ///
    /// The destructor of the future returned by this function will kill
    /// the child if [`kill_on_drop`] is set to true.
    ///
    /// [`kill_on_drop`]: fn@Self::kill_on_drop
    ///
    /// # Errors
    ///
    /// This future will return an error if the child process cannot be spawned
    /// or if there is an error while awaiting its status.
    ///
    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
    /// if the system process limit is reached (which includes other applications
    /// running on the system).
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// async fn run_ls() -> std::process::ExitStatus {
    ///     Command::new("ls")
    ///         .status()
    ///         .await
    ///         .expect("ls command failed to run")
    /// }
    /// ```
    pub fn status(&mut self) -> impl Future<Output = io::Result<ExitStatus>> {
        let child = self.spawn();

        async {
            let mut child = child?;

            // Ensure we close any stdio handles so we can't deadlock
            // waiting on the child which may be waiting to read/write
            // to a pipe we're holding.
            child.stdin.take();
            child.stdout.take();
            child.stderr.take();

            child.wait().await
        }
    }

    /// Executes the command as a child process, waiting for it to finish and
    /// collecting all of its output.
    ///
    /// > **Note**: this method, unlike the standard library, will
    /// > unconditionally configure the stdout/stderr handles to be pipes, even
    /// > if they have been previously configured. If this is not desired then
    /// > the `spawn` method should be used in combination with the
    /// > `wait_with_output` method on child.
    ///
    /// This method will return a future representing the collection of the
    /// child process's stdout/stderr. It will resolve to
    /// the `Output` type in the standard library, containing `stdout` and
    /// `stderr` as `Vec<u8>` along with an `ExitStatus` representing how the
    /// process exited.
    ///
    /// All I/O this child does will be associated with the current default
    /// event loop.
    ///
    /// The destructor of the future returned by this function will kill
    /// the child if [`kill_on_drop`] is set to true.
    ///
    /// [`kill_on_drop`]: fn@Self::kill_on_drop
    ///
    /// # Errors
    ///
    /// This future will return an error if the child process cannot be spawned
    /// or if there is an error while awaiting its status.
    ///
    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
    /// if the system process limit is reached (which includes other applications
    /// running on the system).
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```no_run
    /// use tokio::process::Command;
    ///
    /// async fn run_ls() {
    ///     let output: std::process::Output = Command::new("ls")
    ///         .output()
    ///         .await
    ///         .expect("ls command failed to run");
    ///     println!("stderr of ls: {:?}", output.stderr);
    /// }
    /// ```
    pub fn output(&mut self) -> impl Future<Output = io::Result<Output>> {
        self.std.stdout(Stdio::piped());
        self.std.stderr(Stdio::piped());

        let child = self.spawn();

        async { child?.wait_with_output().await }
    }
}

impl From<StdCommand> for Command {
    fn from(std: StdCommand) -> Command {
        Command {
            std,
            kill_on_drop: false,
        }
    }
}

/// A drop guard which can ensure the child process is killed on drop if specified.
#[derive(Debug)]
struct ChildDropGuard<T: Kill> {
    inner: T,
    kill_on_drop: bool,
}

impl<T: Kill> Kill for ChildDropGuard<T> {
    fn kill(&mut self) -> io::Result<()> {
        let ret = self.inner.kill();

        if ret.is_ok() {
            self.kill_on_drop = false;
        }

        ret
    }
}

impl<T: Kill> Drop for ChildDropGuard<T> {
    fn drop(&mut self) {
        if self.kill_on_drop {
            drop(self.kill());
        }
    }
}

impl<T, E, F> Future for ChildDropGuard<F>
where
    F: Future<Output = Result<T, E>> + Kill + Unpin,
{
    type Output = Result<T, E>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        // Keep track of task budget
        let coop = ready!(crate::coop::poll_proceed(cx));

        let ret = Pin::new(&mut self.inner).poll(cx);

        if let Poll::Ready(Ok(_)) = ret {
            // Avoid the overhead of trying to kill a reaped process
            self.kill_on_drop = false;
        }

        if ret.is_ready() {
            coop.made_progress();
        }

        ret
    }
}

/// Keeps track of the exit status of a child process without worrying about
/// polling the underlying futures even after they have completed.
#[derive(Debug)]
enum FusedChild {
    Child(ChildDropGuard<imp::Child>),
    Done(ExitStatus),
}

/// Representation of a child process spawned onto an event loop.
///
/// # Caveats
/// Similar to the behavior to the standard library, and unlike the futures
/// paradigm of dropping-implies-cancellation, a spawned process will, by
/// default, continue to execute even after the `Child` handle has been dropped.
///
/// The `Command::kill_on_drop` method can be used to modify this behavior
/// and kill the child process if the `Child` wrapper is dropped before it
/// has exited.
#[derive(Debug)]
pub struct Child {
    child: FusedChild,

    /// The handle for writing to the child's standard input (stdin), if it has
    /// been captured. To avoid partially moving the `child` and thus blocking
    /// yourself from calling functions on `child` while using `stdin`, you might
    /// find it helpful to do:
    ///
    /// ```no_run
    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
    /// let stdin = child.stdin.take().unwrap();
    /// ```
    pub stdin: Option<ChildStdin>,

    /// The handle for reading from the child's standard output (stdout), if it
    /// has been captured. You might find it helpful to do
    ///
    /// ```no_run
    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
    /// let stdout = child.stdout.take().unwrap();
    /// ```
    ///
    /// to avoid partially moving the `child` and thus blocking yourself from calling
    /// functions on `child` while using `stdout`.
    pub stdout: Option<ChildStdout>,

    /// The handle for reading from the child's standard error (stderr), if it
    /// has been captured. You might find it helpful to do
    ///
    /// ```no_run
    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
    /// let stderr = child.stderr.take().unwrap();
    /// ```
    ///
    /// to avoid partially moving the `child` and thus blocking yourself from calling
    /// functions on `child` while using `stderr`.
    pub stderr: Option<ChildStderr>,
}

impl Child {
    /// Returns the OS-assigned process identifier associated with this child
    /// while it is still running.
    ///
    /// Once the child has been polled to completion this will return `None`.
    /// This is done to avoid confusion on platforms like Unix where the OS
    /// identifier could be reused once the process has completed.
    pub fn id(&self) -> Option<u32> {
        match &self.child {
            FusedChild::Child(child) => Some(child.inner.id()),
            FusedChild::Done(_) => None,
        }
    }

    /// Extracts the raw handle of the process associated with this child while
    /// it is still running. Returns `None` if the child has exited.
    #[cfg(windows)]
    pub fn raw_handle(&self) -> Option<RawHandle> {
        match &self.child {
            FusedChild::Child(c) => Some(c.inner.as_raw_handle()),
            FusedChild::Done(_) => None,
        }
    }

    /// Attempts to force the child to exit, but does not wait for the request
    /// to take effect.
    ///
    /// On Unix platforms, this is the equivalent to sending a SIGKILL. Note
    /// that on Unix platforms it is possible for a zombie process to remain
    /// after a kill is sent; to avoid this, the caller should ensure that either
    /// `child.wait().await` or `child.try_wait()` is invoked successfully.
    pub fn start_kill(&mut self) -> io::Result<()> {
        match &mut self.child {
            FusedChild::Child(child) => child.kill(),
            FusedChild::Done(_) => Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "invalid argument: can't kill an exited process",
            )),
        }
    }

    /// Forces the child to exit.
    ///
    /// This is equivalent to sending a SIGKILL on unix platforms.
    ///
    /// If the child has to be killed remotely, it is possible to do it using
    /// a combination of the select! macro and a oneshot channel. In the following
    /// example, the child will run until completion unless a message is sent on
    /// the oneshot channel. If that happens, the child is killed immediately
    /// using the `.kill()` method.
    ///
    /// ```no_run
    /// use tokio::process::Command;
    /// use tokio::sync::oneshot::channel;
    ///
    /// #[tokio::main]
    /// async fn main() {
    ///     let (send, recv) = channel::<()>();
    ///     let mut child = Command::new("sleep").arg("1").spawn().unwrap();
    ///     tokio::spawn(async move { send.send(()) });
    ///     tokio::select! {
    ///         _ = child.wait() => {}
    ///         _ = recv => child.kill().await.expect("kill failed"),
    ///     }
    /// }
    /// ```
    pub async fn kill(&mut self) -> io::Result<()> {
        self.start_kill()?;
        self.wait().await?;
        Ok(())
    }

    /// Waits for the child to exit completely, returning the status that it
    /// exited with. This function will continue to have the same return value
    /// after it has been called at least once.
    ///
    /// The stdin handle to the child process, if any, will be closed
    /// before waiting. This helps avoid deadlock: it ensures that the
    /// child does not block waiting for input from the parent, while
    /// the parent waits for the child to exit.
    ///
    /// If the caller wishes to explicitly control when the child's stdin
    /// handle is closed, they may `.take()` it before calling `.wait()`:
    ///
    /// ```
    /// # #[cfg(not(unix))]fn main(){}
    /// # #[cfg(unix)]
    /// use tokio::io::AsyncWriteExt;
    /// # #[cfg(unix)]
    /// use tokio::process::Command;
    /// # #[cfg(unix)]
    /// use std::process::Stdio;
    ///
    /// # #[cfg(unix)]
    /// #[tokio::main]
    /// async fn main() {
    ///     let mut child = Command::new("cat")
    ///         .stdin(Stdio::piped())
    ///         .spawn()
    ///         .unwrap();
    ///
    ///     let mut stdin = child.stdin.take().unwrap();
    ///     tokio::spawn(async move {
    ///         // do something with stdin here...
    ///         stdin.write_all(b"hello world\n").await.unwrap();
    ///
    ///         // then drop when finished
    ///         drop(stdin);
    ///     });
    ///
    ///     // wait for the process to complete
    ///     let _ = child.wait().await;
    /// }
    /// ```
    pub async fn wait(&mut self) -> io::Result<ExitStatus> {
        // Ensure stdin is closed so the child isn't stuck waiting on
        // input while the parent is waiting for it to exit.
        drop(self.stdin.take());

        match &mut self.child {
            FusedChild::Done(exit) => Ok(*exit),
            FusedChild::Child(child) => {
                let ret = child.await;

                if let Ok(exit) = ret {
                    self.child = FusedChild::Done(exit);
                }

                ret
            }
        }
    }

    /// Attempts to collect the exit status of the child if it has already
    /// exited.
    ///
    /// This function will not block the calling thread and will only
    /// check to see if the child process has exited or not. If the child has
    /// exited then on Unix the process ID is reaped. This function is
    /// guaranteed to repeatedly return a successful exit status so long as the
    /// child has already exited.
    ///
    /// If the child has exited, then `Ok(Some(status))` is returned. If the
    /// exit status is not available at this time then `Ok(None)` is returned.
    /// If an error occurs, then that error is returned.
    ///
    /// Note that unlike `wait`, this function will not attempt to drop stdin,
    /// nor will it wake the current task if the child exits.
    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
        match &mut self.child {
            FusedChild::Done(exit) => Ok(Some(*exit)),
            FusedChild::Child(guard) => {
                let ret = guard.inner.try_wait();

                if let Ok(Some(exit)) = ret {
                    // Avoid the overhead of trying to kill a reaped process
                    guard.kill_on_drop = false;
                    self.child = FusedChild::Done(exit);
                }

                ret
            }
        }
    }

    /// Returns a future that will resolve to an `Output`, containing the exit
    /// status, stdout, and stderr of the child process.
    ///
    /// The returned future will simultaneously waits for the child to exit and
    /// collect all remaining output on the stdout/stderr handles, returning an
    /// `Output` instance.
    ///
    /// The stdin handle to the child process, if any, will be closed before
    /// waiting. This helps avoid deadlock: it ensures that the child does not
    /// block waiting for input from the parent, while the parent waits for the
    /// child to exit.
    ///
    /// By default, stdin, stdout and stderr are inherited from the parent. In
    /// order to capture the output into this `Output` it is necessary to create
    /// new pipes between parent and child. Use `stdout(Stdio::piped())` or
    /// `stderr(Stdio::piped())`, respectively, when creating a `Command`.
    pub async fn wait_with_output(mut self) -> io::Result<Output> {
        use crate::future::try_join3;

        async fn read_to_end<A: AsyncRead + Unpin>(io: &mut Option<A>) -> io::Result<Vec<u8>> {
            let mut vec = Vec::new();
            if let Some(io) = io.as_mut() {
                crate::io::util::read_to_end(io, &mut vec).await?;
            }
            Ok(vec)
        }

        let mut stdout_pipe = self.stdout.take();
        let mut stderr_pipe = self.stderr.take();

        let stdout_fut = read_to_end(&mut stdout_pipe);
        let stderr_fut = read_to_end(&mut stderr_pipe);

        let (status, stdout, stderr) = try_join3(self.wait(), stdout_fut, stderr_fut).await?;

        // Drop happens after `try_join` due to <https://github.com/tokio-rs/tokio/issues/4309>
        drop(stdout_pipe);
        drop(stderr_pipe);

        Ok(Output {
            status,
            stdout,
            stderr,
        })
    }
}

/// The standard input stream for spawned children.
///
/// This type implements the `AsyncWrite` trait to pass data to the stdin handle of
/// handle of a child process asynchronously.
#[derive(Debug)]
pub struct ChildStdin {
    inner: imp::ChildStdio,
}

/// The standard output stream for spawned children.
///
/// This type implements the `AsyncRead` trait to read data from the stdout
/// handle of a child process asynchronously.
#[derive(Debug)]
pub struct ChildStdout {
    inner: imp::ChildStdio,
}

/// The standard error stream for spawned children.
///
/// This type implements the `AsyncRead` trait to read data from the stderr
/// handle of a child process asynchronously.
#[derive(Debug)]
pub struct ChildStderr {
    inner: imp::ChildStdio,
}

impl ChildStdin {
    /// Creates an asynchronous `ChildStdin` from a synchronous one.
    ///
    /// # Errors
    ///
    /// This method may fail if an error is encountered when setting the pipe to
    /// non-blocking mode, or when registering the pipe with the runtime's IO
    /// driver.
    pub fn from_std(inner: std::process::ChildStdin) -> io::Result<Self> {
        Ok(Self {
            inner: imp::stdio(inner)?,
        })
    }
}

impl ChildStdout {
    /// Creates an asynchronous `ChildStderr` from a synchronous one.
    ///
    /// # Errors
    ///
    /// This method may fail if an error is encountered when setting the pipe to
    /// non-blocking mode, or when registering the pipe with the runtime's IO
    /// driver.
    pub fn from_std(inner: std::process::ChildStdout) -> io::Result<Self> {
        Ok(Self {
            inner: imp::stdio(inner)?,
        })
    }
}

impl ChildStderr {
    /// Creates an asynchronous `ChildStderr` from a synchronous one.
    ///
    /// # Errors
    ///
    /// This method may fail if an error is encountered when setting the pipe to
    /// non-blocking mode, or when registering the pipe with the runtime's IO
    /// driver.
    pub fn from_std(inner: std::process::ChildStderr) -> io::Result<Self> {
        Ok(Self {
            inner: imp::stdio(inner)?,
        })
    }
}

impl AsyncWrite for ChildStdin {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.inner.poll_write(cx, buf)
    }

    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Poll::Ready(Ok(()))
    }

    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Poll::Ready(Ok(()))
    }
}

impl AsyncRead for ChildStdout {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        // Safety: pipes support reading into uninitialized memory
        unsafe { self.inner.poll_read(cx, buf) }
    }
}

impl AsyncRead for ChildStderr {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        // Safety: pipes support reading into uninitialized memory
        unsafe { self.inner.poll_read(cx, buf) }
    }
}

impl TryInto<Stdio> for ChildStdin {
    type Error = io::Error;

    fn try_into(self) -> Result<Stdio, Self::Error> {
        imp::convert_to_stdio(self.inner)
    }
}

impl TryInto<Stdio> for ChildStdout {
    type Error = io::Error;

    fn try_into(self) -> Result<Stdio, Self::Error> {
        imp::convert_to_stdio(self.inner)
    }
}

impl TryInto<Stdio> for ChildStderr {
    type Error = io::Error;

    fn try_into(self) -> Result<Stdio, Self::Error> {
        imp::convert_to_stdio(self.inner)
    }
}

#[cfg(unix)]
mod sys {
    use std::os::unix::io::{AsRawFd, RawFd};

    use super::{ChildStderr, ChildStdin, ChildStdout};

    impl AsRawFd for ChildStdin {
        fn as_raw_fd(&self) -> RawFd {
            self.inner.as_raw_fd()
        }
    }

    impl AsRawFd for ChildStdout {
        fn as_raw_fd(&self) -> RawFd {
            self.inner.as_raw_fd()
        }
    }

    impl AsRawFd for ChildStderr {
        fn as_raw_fd(&self) -> RawFd {
            self.inner.as_raw_fd()
        }
    }
}

#[cfg(windows)]
mod sys {
    use std::os::windows::io::{AsRawHandle, RawHandle};

    use super::{ChildStderr, ChildStdin, ChildStdout};

    impl AsRawHandle for ChildStdin {
        fn as_raw_handle(&self) -> RawHandle {
            self.inner.as_raw_handle()
        }
    }

    impl AsRawHandle for ChildStdout {
        fn as_raw_handle(&self) -> RawHandle {
            self.inner.as_raw_handle()
        }
    }

    impl AsRawHandle for ChildStderr {
        fn as_raw_handle(&self) -> RawHandle {
            self.inner.as_raw_handle()
        }
    }
}

#[cfg(all(test, not(loom)))]
mod test {
    use super::kill::Kill;
    use super::ChildDropGuard;

    use futures::future::FutureExt;
    use std::future::Future;
    use std::io;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    struct Mock {
        num_kills: usize,
        num_polls: usize,
        poll_result: Poll<Result<(), ()>>,
    }

    impl Mock {
        fn new() -> Self {
            Self::with_result(Poll::Pending)
        }

        fn with_result(result: Poll<Result<(), ()>>) -> Self {
            Self {
                num_kills: 0,
                num_polls: 0,
                poll_result: result,
            }
        }
    }

    impl Kill for Mock {
        fn kill(&mut self) -> io::Result<()> {
            self.num_kills += 1;
            Ok(())
        }
    }

    impl Future for Mock {
        type Output = Result<(), ()>;

        fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
            let inner = Pin::get_mut(self);
            inner.num_polls += 1;
            inner.poll_result
        }
    }

    #[test]
    fn kills_on_drop_if_specified() {
        let mut mock = Mock::new();

        {
            let guard = ChildDropGuard {
                inner: &mut mock,
                kill_on_drop: true,
            };
            drop(guard);
        }

        assert_eq!(1, mock.num_kills);
        assert_eq!(0, mock.num_polls);
    }

    #[test]
    fn no_kill_on_drop_by_default() {
        let mut mock = Mock::new();

        {
            let guard = ChildDropGuard {
                inner: &mut mock,
                kill_on_drop: false,
            };
            drop(guard);
        }

        assert_eq!(0, mock.num_kills);
        assert_eq!(0, mock.num_polls);
    }

    #[test]
    fn no_kill_if_already_killed() {
        let mut mock = Mock::new();

        {
            let mut guard = ChildDropGuard {
                inner: &mut mock,
                kill_on_drop: true,
            };
            let _ = guard.kill();
            drop(guard);
        }

        assert_eq!(1, mock.num_kills);
        assert_eq!(0, mock.num_polls);
    }

    #[test]
    fn no_kill_if_reaped() {
        let mut mock_pending = Mock::with_result(Poll::Pending);
        let mut mock_reaped = Mock::with_result(Poll::Ready(Ok(())));
        let mut mock_err = Mock::with_result(Poll::Ready(Err(())));

        let waker = futures::task::noop_waker();
        let mut context = Context::from_waker(&waker);
        {
            let mut guard = ChildDropGuard {
                inner: &mut mock_pending,
                kill_on_drop: true,
            };
            let _ = guard.poll_unpin(&mut context);

            let mut guard = ChildDropGuard {
                inner: &mut mock_reaped,
                kill_on_drop: true,
            };
            let _ = guard.poll_unpin(&mut context);

            let mut guard = ChildDropGuard {
                inner: &mut mock_err,
                kill_on_drop: true,
            };
            let _ = guard.poll_unpin(&mut context);
        }

        assert_eq!(1, mock_pending.num_kills);
        assert_eq!(1, mock_pending.num_polls);

        assert_eq!(0, mock_reaped.num_kills);
        assert_eq!(1, mock_reaped.num_polls);

        assert_eq!(1, mock_err.num_kills);
        assert_eq!(1, mock_err.num_polls);
    }
}