aboutsummaryrefslogtreecommitdiff
path: root/run-command.c
blob: 014b2165b5a2f92ff18869effafd4c6df01b33eb (plain)
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
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
#include "cache.h"
#include "run-command.h"
#include "exec_cmd.h"
#include "sigchain.h"
#include "argv-array.h"
#include "thread-utils.h"
#include "strbuf.h"

void child_process_init(struct child_process *child)
{
	memset(child, 0, sizeof(*child));
	argv_array_init(&child->args);
	argv_array_init(&child->env_array);
}

void child_process_clear(struct child_process *child)
{
	argv_array_clear(&child->args);
	argv_array_clear(&child->env_array);
}

struct child_to_clean {
	pid_t pid;
	struct child_process *process;
	struct child_to_clean *next;
};
static struct child_to_clean *children_to_clean;
static int installed_child_cleanup_handler;

static void cleanup_children(int sig, int in_signal)
{
	struct child_to_clean *children_to_wait_for = NULL;

	while (children_to_clean) {
		struct child_to_clean *p = children_to_clean;
		children_to_clean = p->next;

		if (p->process && !in_signal) {
			struct child_process *process = p->process;
			if (process->clean_on_exit_handler) {
				trace_printf(
					"trace: run_command: running exit handler for pid %"
					PRIuMAX, (uintmax_t)p->pid
				);
				process->clean_on_exit_handler(process);
			}
		}

		kill(p->pid, sig);

		if (p->process && p->process->wait_after_clean) {
			p->next = children_to_wait_for;
			children_to_wait_for = p;
		} else {
			if (!in_signal)
				free(p);
		}
	}

	while (children_to_wait_for) {
		struct child_to_clean *p = children_to_wait_for;
		children_to_wait_for = p->next;

		while (waitpid(p->pid, NULL, 0) < 0 && errno == EINTR)
			; /* spin waiting for process exit or error */

		if (!in_signal)
			free(p);
	}
}

static void cleanup_children_on_signal(int sig)
{
	cleanup_children(sig, 1);
	sigchain_pop(sig);
	raise(sig);
}

static void cleanup_children_on_exit(void)
{
	cleanup_children(SIGTERM, 0);
}

static void mark_child_for_cleanup(pid_t pid, struct child_process *process)
{
	struct child_to_clean *p = xmalloc(sizeof(*p));
	p->pid = pid;
	p->process = process;
	p->next = children_to_clean;
	children_to_clean = p;

	if (!installed_child_cleanup_handler) {
		atexit(cleanup_children_on_exit);
		sigchain_push_common(cleanup_children_on_signal);
		installed_child_cleanup_handler = 1;
	}
}

static void clear_child_for_cleanup(pid_t pid)
{
	struct child_to_clean **pp;

	for (pp = &children_to_clean; *pp; pp = &(*pp)->next) {
		struct child_to_clean *clean_me = *pp;

		if (clean_me->pid == pid) {
			*pp = clean_me->next;
			free(clean_me);
			return;
		}
	}
}

static inline void close_pair(int fd[2])
{
	close(fd[0]);
	close(fd[1]);
}

int is_executable(const char *name)
{
	struct stat st;

	if (stat(name, &st) || /* stat, not lstat */
	    !S_ISREG(st.st_mode))
		return 0;

#if defined(GIT_WINDOWS_NATIVE)
	/*
	 * On Windows there is no executable bit. The file extension
	 * indicates whether it can be run as an executable, and Git
	 * has special-handling to detect scripts and launch them
	 * through the indicated script interpreter. We test for the
	 * file extension first because virus scanners may make
	 * it quite expensive to open many files.
	 */
	if (ends_with(name, ".exe"))
		return S_IXUSR;

{
	/*
	 * Now that we know it does not have an executable extension,
	 * peek into the file instead.
	 */
	char buf[3] = { 0 };
	int n;
	int fd = open(name, O_RDONLY);
	st.st_mode &= ~S_IXUSR;
	if (fd >= 0) {
		n = read(fd, buf, 2);
		if (n == 2)
			/* look for a she-bang */
			if (!strcmp(buf, "#!"))
				st.st_mode |= S_IXUSR;
		close(fd);
	}
}
#endif
	return st.st_mode & S_IXUSR;
}

/*
 * Search $PATH for a command.  This emulates the path search that
 * execvp would perform, without actually executing the command so it
 * can be used before fork() to prepare to run a command using
 * execve() or after execvp() to diagnose why it failed.
 *
 * The caller should ensure that file contains no directory
 * separators.
 *
 * Returns the path to the command, as found in $PATH or NULL if the
 * command could not be found.  The caller inherits ownership of the memory
 * used to store the resultant path.
 *
 * This should not be used on Windows, where the $PATH search rules
 * are more complicated (e.g., a search for "foo" should find
 * "foo.exe").
 */
static char *locate_in_PATH(const char *file)
{
	const char *p = getenv("PATH");
	struct strbuf buf = STRBUF_INIT;

	if (!p || !*p)
		return NULL;

	while (1) {
		const char *end = strchrnul(p, ':');

		strbuf_reset(&buf);

		/* POSIX specifies an empty entry as the current directory. */
		if (end != p) {
			strbuf_add(&buf, p, end - p);
			strbuf_addch(&buf, '/');
		}
		strbuf_addstr(&buf, file);

		if (is_executable(buf.buf))
			return strbuf_detach(&buf, NULL);

		if (!*end)
			break;
		p = end + 1;
	}

	strbuf_release(&buf);
	return NULL;
}

static int exists_in_PATH(const char *file)
{
	char *r = locate_in_PATH(file);
	free(r);
	return r != NULL;
}

int sane_execvp(const char *file, char * const argv[])
{
	if (!execvp(file, argv))
		return 0; /* cannot happen ;-) */

	/*
	 * When a command can't be found because one of the directories
	 * listed in $PATH is unsearchable, execvp reports EACCES, but
	 * careful usability testing (read: analysis of occasional bug
	 * reports) reveals that "No such file or directory" is more
	 * intuitive.
	 *
	 * We avoid commands with "/", because execvp will not do $PATH
	 * lookups in that case.
	 *
	 * The reassignment of EACCES to errno looks like a no-op below,
	 * but we need to protect against exists_in_PATH overwriting errno.
	 */
	if (errno == EACCES && !strchr(file, '/'))
		errno = exists_in_PATH(file) ? EACCES : ENOENT;
	else if (errno == ENOTDIR && !strchr(file, '/'))
		errno = ENOENT;
	return -1;
}

static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
{
	if (!argv[0])
		die("BUG: shell command is empty");

	if (strcspn(argv[0], "|&;<>()$`\\\"' \t\n*?[#~=%") != strlen(argv[0])) {
#ifndef GIT_WINDOWS_NATIVE
		argv_array_push(out, SHELL_PATH);
#else
		argv_array_push(out, "sh");
#endif
		argv_array_push(out, "-c");

		/*
		 * If we have no extra arguments, we do not even need to
		 * bother with the "$@" magic.
		 */
		if (!argv[1])
			argv_array_push(out, argv[0]);
		else
			argv_array_pushf(out, "%s \"$@\"", argv[0]);
	}

	argv_array_pushv(out, argv);
	return out->argv;
}

#ifndef GIT_WINDOWS_NATIVE
static int child_notifier = -1;

enum child_errcode {
	CHILD_ERR_CHDIR,
	CHILD_ERR_DUP2,
	CHILD_ERR_CLOSE,
	CHILD_ERR_SIGPROCMASK,
	CHILD_ERR_ENOENT,
	CHILD_ERR_SILENT,
	CHILD_ERR_ERRNO
};

struct child_err {
	enum child_errcode err;
	int syserr; /* errno */
};

static void child_die(enum child_errcode err)
{
	struct child_err buf;

	buf.err = err;
	buf.syserr = errno;

	/* write(2) on buf smaller than PIPE_BUF (min 512) is atomic: */
	xwrite(child_notifier, &buf, sizeof(buf));
	_exit(1);
}

static void child_dup2(int fd, int to)
{
	if (dup2(fd, to) < 0)
		child_die(CHILD_ERR_DUP2);
}

static void child_close(int fd)
{
	if (close(fd))
		child_die(CHILD_ERR_CLOSE);
}

static void child_close_pair(int fd[2])
{
	child_close(fd[0]);
	child_close(fd[1]);
}

/*
 * parent will make it look like the child spewed a fatal error and died
 * this is needed to prevent changes to t0061.
 */
static void fake_fatal(const char *err, va_list params)
{
	vreportf("fatal: ", err, params);
}

static void child_error_fn(const char *err, va_list params)
{
	const char msg[] = "error() should not be called in child\n";
	xwrite(2, msg, sizeof(msg) - 1);
}

static void child_warn_fn(const char *err, va_list params)
{
	const char msg[] = "warn() should not be called in child\n";
	xwrite(2, msg, sizeof(msg) - 1);
}

static void NORETURN child_die_fn(const char *err, va_list params)
{
	const char msg[] = "die() should not be called in child\n";
	xwrite(2, msg, sizeof(msg) - 1);
	_exit(2);
}

/* this runs in the parent process */
static void child_err_spew(struct child_process *cmd, struct child_err *cerr)
{
	static void (*old_errfn)(const char *err, va_list params);

	old_errfn = get_error_routine();
	set_error_routine(fake_fatal);
	errno = cerr->syserr;

	switch (cerr->err) {
	case CHILD_ERR_CHDIR:
		error_errno("exec '%s': cd to '%s' failed",
			    cmd->argv[0], cmd->dir);
		break;
	case CHILD_ERR_DUP2:
		error_errno("dup2() in child failed");
		break;
	case CHILD_ERR_CLOSE:
		error_errno("close() in child failed");
		break;
	case CHILD_ERR_SIGPROCMASK:
		error_errno("sigprocmask failed restoring signals");
		break;
	case CHILD_ERR_ENOENT:
		error_errno("cannot run %s", cmd->argv[0]);
		break;
	case CHILD_ERR_SILENT:
		break;
	case CHILD_ERR_ERRNO:
		error_errno("cannot exec '%s'", cmd->argv[0]);
		break;
	}
	set_error_routine(old_errfn);
}

static void prepare_cmd(struct argv_array *out, const struct child_process *cmd)
{
	if (!cmd->argv[0])
		die("BUG: command is empty");

	/*
	 * Add SHELL_PATH so in the event exec fails with ENOEXEC we can
	 * attempt to interpret the command with 'sh'.
	 */
	argv_array_push(out, SHELL_PATH);

	if (cmd->git_cmd) {
		argv_array_push(out, "git");
		argv_array_pushv(out, cmd->argv);
	} else if (cmd->use_shell) {
		prepare_shell_cmd(out, cmd->argv);
	} else {
		argv_array_pushv(out, cmd->argv);
	}

	/*
	 * If there are no '/' characters in the command then perform a path
	 * lookup and use the resolved path as the command to exec.  If there
	 * are no '/' characters or if the command wasn't found in the path,
	 * have exec attempt to invoke the command directly.
	 */
	if (!strchr(out->argv[1], '/')) {
		char *program = locate_in_PATH(out->argv[1]);
		if (program) {
			free((char *)out->argv[1]);
			out->argv[1] = program;
		}
	}
}

static char **prep_childenv(const char *const *deltaenv)
{
	extern char **environ;
	char **childenv;
	struct string_list env = STRING_LIST_INIT_DUP;
	struct strbuf key = STRBUF_INIT;
	const char *const *p;
	int i;

	/* Construct a sorted string list consisting of the current environ */
	for (p = (const char *const *) environ; p && *p; p++) {
		const char *equals = strchr(*p, '=');

		if (equals) {
			strbuf_reset(&key);
			strbuf_add(&key, *p, equals - *p);
			string_list_append(&env, key.buf)->util = (void *) *p;
		} else {
			string_list_append(&env, *p)->util = (void *) *p;
		}
	}
	string_list_sort(&env);

	/* Merge in 'deltaenv' with the current environ */
	for (p = deltaenv; p && *p; p++) {
		const char *equals = strchr(*p, '=');

		if (equals) {
			/* ('key=value'), insert or replace entry */
			strbuf_reset(&key);
			strbuf_add(&key, *p, equals - *p);
			string_list_insert(&env, key.buf)->util = (void *) *p;
		} else {
			/* otherwise ('key') remove existing entry */
			string_list_remove(&env, *p, 0);
		}
	}

	/* Create an array of 'char *' to be used as the childenv */
	ALLOC_ARRAY(childenv, env.nr + 1);
	for (i = 0; i < env.nr; i++)
		childenv[i] = env.items[i].util;
	childenv[env.nr] = NULL;

	string_list_clear(&env, 0);
	strbuf_release(&key);
	return childenv;
}

struct atfork_state {
#ifndef NO_PTHREADS
	int cs;
#endif
	sigset_t old;
};

#ifndef NO_PTHREADS
static void bug_die(int err, const char *msg)
{
	if (err) {
		errno = err;
		die_errno("BUG: %s", msg);
	}
}
#endif

static void atfork_prepare(struct atfork_state *as)
{
	sigset_t all;

	if (sigfillset(&all))
		die_errno("sigfillset");
#ifdef NO_PTHREADS
	if (sigprocmask(SIG_SETMASK, &all, &as->old))
		die_errno("sigprocmask");
#else
	bug_die(pthread_sigmask(SIG_SETMASK, &all, &as->old),
		"blocking all signals");
	bug_die(pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &as->cs),
		"disabling cancellation");
#endif
}

static void atfork_parent(struct atfork_state *as)
{
#ifdef NO_PTHREADS
	if (sigprocmask(SIG_SETMASK, &as->old, NULL))
		die_errno("sigprocmask");
#else
	bug_die(pthread_setcancelstate(as->cs, NULL),
		"re-enabling cancellation");
	bug_die(pthread_sigmask(SIG_SETMASK, &as->old, NULL),
		"restoring signal mask");
#endif
}
#endif /* GIT_WINDOWS_NATIVE */

static inline void set_cloexec(int fd)
{
	int flags = fcntl(fd, F_GETFD);
	if (flags >= 0)
		fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
}

static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
{
	int status, code = -1;
	pid_t waiting;
	int failed_errno = 0;

	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
		;	/* nothing */
	if (in_signal)
		return 0;

	if (waiting < 0) {
		failed_errno = errno;
		error_errno("waitpid for %s failed", argv0);
	} else if (waiting != pid) {
		error("waitpid is confused (%s)", argv0);
	} else if (WIFSIGNALED(status)) {
		code = WTERMSIG(status);
		if (code != SIGINT && code != SIGQUIT && code != SIGPIPE)
			error("%s died of signal %d", argv0, code);
		/*
		 * This return value is chosen so that code & 0xff
		 * mimics the exit code that a POSIX shell would report for
		 * a program that died from this signal.
		 */
		code += 128;
	} else if (WIFEXITED(status)) {
		code = WEXITSTATUS(status);
	} else {
		error("waitpid is confused (%s)", argv0);
	}

	clear_child_for_cleanup(pid);

	errno = failed_errno;
	return code;
}

int start_command(struct child_process *cmd)
{
	int need_in, need_out, need_err;
	int fdin[2], fdout[2], fderr[2];
	int failed_errno;
	char *str;

	if (!cmd->argv)
		cmd->argv = cmd->args.argv;
	if (!cmd->env)
		cmd->env = cmd->env_array.argv;

	/*
	 * In case of errors we must keep the promise to close FDs
	 * that have been passed in via ->in and ->out.
	 */

	need_in = !cmd->no_stdin && cmd->in < 0;
	if (need_in) {
		if (pipe(fdin) < 0) {
			failed_errno = errno;
			if (cmd->out > 0)
				close(cmd->out);
			str = "standard input";
			goto fail_pipe;
		}
		cmd->in = fdin[1];
	}

	need_out = !cmd->no_stdout
		&& !cmd->stdout_to_stderr
		&& cmd->out < 0;
	if (need_out) {
		if (pipe(fdout) < 0) {
			failed_errno = errno;
			if (need_in)
				close_pair(fdin);
			else if (cmd->in)
				close(cmd->in);
			str = "standard output";
			goto fail_pipe;
		}
		cmd->out = fdout[0];
	}

	need_err = !cmd->no_stderr && cmd->err < 0;
	if (need_err) {
		if (pipe(fderr) < 0) {
			failed_errno = errno;
			if (need_in)
				close_pair(fdin);
			else if (cmd->in)
				close(cmd->in);
			if (need_out)
				close_pair(fdout);
			else if (cmd->out)
				close(cmd->out);
			str = "standard error";
fail_pipe:
			error("cannot create %s pipe for %s: %s",
				str, cmd->argv[0], strerror(failed_errno));
			child_process_clear(cmd);
			errno = failed_errno;
			return -1;
		}
		cmd->err = fderr[0];
	}

	trace_argv_printf(cmd->argv, "trace: run_command:");
	fflush(NULL);

#ifndef GIT_WINDOWS_NATIVE
{
	int notify_pipe[2];
	int null_fd = -1;
	char **childenv;
	struct argv_array argv = ARGV_ARRAY_INIT;
	struct child_err cerr;
	struct atfork_state as;

	if (pipe(notify_pipe))
		notify_pipe[0] = notify_pipe[1] = -1;

	if (cmd->no_stdin || cmd->no_stdout || cmd->no_stderr) {
		null_fd = open("/dev/null", O_RDWR | O_CLOEXEC);
		if (null_fd < 0)
			die_errno(_("open /dev/null failed"));
		set_cloexec(null_fd);
	}

	prepare_cmd(&argv, cmd);
	childenv = prep_childenv(cmd->env);
	atfork_prepare(&as);

	/*
	 * NOTE: In order to prevent deadlocking when using threads special
	 * care should be taken with the function calls made in between the
	 * fork() and exec() calls.  No calls should be made to functions which
	 * require acquiring a lock (e.g. malloc) as the lock could have been
	 * held by another thread at the time of forking, causing the lock to
	 * never be released in the child process.  This means only
	 * Async-Signal-Safe functions are permitted in the child.
	 */
	cmd->pid = fork();
	failed_errno = errno;
	if (!cmd->pid) {
		int sig;
		/*
		 * Ensure the default die/error/warn routines do not get
		 * called, they can take stdio locks and malloc.
		 */
		set_die_routine(child_die_fn);
		set_error_routine(child_error_fn);
		set_warn_routine(child_warn_fn);

		close(notify_pipe[0]);
		set_cloexec(notify_pipe[1]);
		child_notifier = notify_pipe[1];

		if (cmd->no_stdin)
			child_dup2(null_fd, 0);
		else if (need_in) {
			child_dup2(fdin[0], 0);
			child_close_pair(fdin);
		} else if (cmd->in) {
			child_dup2(cmd->in, 0);
			child_close(cmd->in);
		}

		if (cmd->no_stderr)
			child_dup2(null_fd, 2);
		else if (need_err) {
			child_dup2(fderr[1], 2);
			child_close_pair(fderr);
		} else if (cmd->err > 1) {
			child_dup2(cmd->err, 2);
			child_close(cmd->err);
		}

		if (cmd->no_stdout)
			child_dup2(null_fd, 1);
		else if (cmd->stdout_to_stderr)
			child_dup2(2, 1);
		else if (need_out) {
			child_dup2(fdout[1], 1);
			child_close_pair(fdout);
		} else if (cmd->out > 1) {
			child_dup2(cmd->out, 1);
			child_close(cmd->out);
		}

		if (cmd->dir && chdir(cmd->dir))
			child_die(CHILD_ERR_CHDIR);

		/*
		 * restore default signal handlers here, in case
		 * we catch a signal right before execve below
		 */
		for (sig = 1; sig < NSIG; sig++) {
			/* ignored signals get reset to SIG_DFL on execve */
			if (signal(sig, SIG_DFL) == SIG_IGN)
				signal(sig, SIG_IGN);
		}

		if (sigprocmask(SIG_SETMASK, &as.old, NULL) != 0)
			child_die(CHILD_ERR_SIGPROCMASK);

		/*
		 * Attempt to exec using the command and arguments starting at
		 * argv.argv[1].  argv.argv[0] contains SHELL_PATH which will
		 * be used in the event exec failed with ENOEXEC at which point
		 * we will try to interpret the command using 'sh'.
		 */
		execve(argv.argv[1], (char *const *) argv.argv + 1,
		       (char *const *) childenv);
		if (errno == ENOEXEC)
			execve(argv.argv[0], (char *const *) argv.argv,
			       (char *const *) childenv);

		if (errno == ENOENT) {
			if (cmd->silent_exec_failure)
				child_die(CHILD_ERR_SILENT);
			child_die(CHILD_ERR_ENOENT);
		} else {
			child_die(CHILD_ERR_ERRNO);
		}
	}
	atfork_parent(&as);
	if (cmd->pid < 0)
		error_errno("cannot fork() for %s", cmd->argv[0]);
	else if (cmd->clean_on_exit)
		mark_child_for_cleanup(cmd->pid, cmd);

	/*
	 * Wait for child's exec. If the exec succeeds (or if fork()
	 * failed), EOF is seen immediately by the parent. Otherwise, the
	 * child process sends a child_err struct.
	 * Note that use of this infrastructure is completely advisory,
	 * therefore, we keep error checks minimal.
	 */
	close(notify_pipe[1]);
	if (xread(notify_pipe[0], &cerr, sizeof(cerr)) == sizeof(cerr)) {
		/*
		 * At this point we know that fork() succeeded, but exec()
		 * failed. Errors have been reported to our stderr.
		 */
		wait_or_whine(cmd->pid, cmd->argv[0], 0);
		child_err_spew(cmd, &cerr);
		failed_errno = errno;
		cmd->pid = -1;
	}
	close(notify_pipe[0]);

	if (null_fd >= 0)
		close(null_fd);
	argv_array_clear(&argv);
	free(childenv);
}
#else
{
	int fhin = 0, fhout = 1, fherr = 2;
	const char **sargv = cmd->argv;
	struct argv_array nargv = ARGV_ARRAY_INIT;

	if (cmd->no_stdin)
		fhin = open("/dev/null", O_RDWR);
	else if (need_in)
		fhin = dup(fdin[0]);
	else if (cmd->in)
		fhin = dup(cmd->in);

	if (cmd->no_stderr)
		fherr = open("/dev/null", O_RDWR);
	else if (need_err)
		fherr = dup(fderr[1]);
	else if (cmd->err > 2)
		fherr = dup(cmd->err);

	if (cmd->no_stdout)
		fhout = open("/dev/null", O_RDWR);
	else if (cmd->stdout_to_stderr)
		fhout = dup(fherr);
	else if (need_out)
		fhout = dup(fdout[1]);
	else if (cmd->out > 1)
		fhout = dup(cmd->out);

	if (cmd->git_cmd)
		cmd->argv = prepare_git_cmd(&nargv, cmd->argv);
	else if (cmd->use_shell)
		cmd->argv = prepare_shell_cmd(&nargv, cmd->argv);

	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, (char**) cmd->env,
			cmd->dir, fhin, fhout, fherr);
	failed_errno = errno;
	if (cmd->pid < 0 && (!cmd->silent_exec_failure || errno != ENOENT))
		error_errno("cannot spawn %s", cmd->argv[0]);
	if (cmd->clean_on_exit && cmd->pid >= 0)
		mark_child_for_cleanup(cmd->pid, cmd);

	argv_array_clear(&nargv);
	cmd->argv = sargv;
	if (fhin != 0)
		close(fhin);
	if (fhout != 1)
		close(fhout);
	if (fherr != 2)
		close(fherr);
}
#endif

	if (cmd->pid < 0) {
		if (need_in)
			close_pair(fdin);
		else if (cmd->in)
			close(cmd->in);
		if (need_out)
			close_pair(fdout);
		else if (cmd->out)
			close(cmd->out);
		if (need_err)
			close_pair(fderr);
		else if (cmd->err)
			close(cmd->err);
		child_process_clear(cmd);
		errno = failed_errno;
		return -1;
	}

	if (need_in)
		close(fdin[0]);
	else if (cmd->in)
		close(cmd->in);

	if (need_out)
		close(fdout[1]);
	else if (cmd->out)
		close(cmd->out);

	if (need_err)
		close(fderr[1]);
	else if (cmd->err)
		close(cmd->err);

	return 0;
}

int finish_command(struct child_process *cmd)
{
	int ret = wait_or_whine(cmd->pid, cmd->argv[0], 0);
	child_process_clear(cmd);
	return ret;
}

int finish_command_in_signal(struct child_process *cmd)
{
	return wait_or_whine(cmd->pid, cmd->argv[0], 1);
}


int run_command(struct child_process *cmd)
{
	int code;

	if (cmd->out < 0 || cmd->err < 0)
		die("BUG: run_command with a pipe can cause deadlock");

	code = start_command(cmd);
	if (code)
		return code;
	return finish_command(cmd);
}

int run_command_v_opt(const char **argv, int opt)
{
	return run_command_v_opt_cd_env(argv, opt, NULL, NULL);
}

int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env)
{
	struct child_process cmd = CHILD_PROCESS_INIT;
	cmd.argv = argv;
	cmd.no_stdin = opt & RUN_COMMAND_NO_STDIN ? 1 : 0;
	cmd.git_cmd = opt & RUN_GIT_CMD ? 1 : 0;
	cmd.stdout_to_stderr = opt & RUN_COMMAND_STDOUT_TO_STDERR ? 1 : 0;
	cmd.silent_exec_failure = opt & RUN_SILENT_EXEC_FAILURE ? 1 : 0;
	cmd.use_shell = opt & RUN_USING_SHELL ? 1 : 0;
	cmd.clean_on_exit = opt & RUN_CLEAN_ON_EXIT ? 1 : 0;
	cmd.dir = dir;
	cmd.env = env;
	return run_command(&cmd);
}

#ifndef NO_PTHREADS
static pthread_t main_thread;
static int main_thread_set;
static pthread_key_t async_key;
static pthread_key_t async_die_counter;

static void *run_thread(void *data)
{
	struct async *async = data;
	intptr_t ret;

	if (async->isolate_sigpipe) {
		sigset_t mask;
		sigemptyset(&mask);
		sigaddset(&mask, SIGPIPE);
		if (pthread_sigmask(SIG_BLOCK, &mask, NULL) < 0) {
			ret = error("unable to block SIGPIPE in async thread");
			return (void *)ret;
		}
	}

	pthread_setspecific(async_key, async);
	ret = async->proc(async->proc_in, async->proc_out, async->data);
	return (void *)ret;
}

static NORETURN void die_async(const char *err, va_list params)
{
	vreportf("fatal: ", err, params);

	if (in_async()) {
		struct async *async = pthread_getspecific(async_key);
		if (async->proc_in >= 0)
			close(async->proc_in);
		if (async->proc_out >= 0)
			close(async->proc_out);
		pthread_exit((void *)128);
	}

	exit(128);
}

static int async_die_is_recursing(void)
{
	void *ret = pthread_getspecific(async_die_counter);
	pthread_setspecific(async_die_counter, (void *)1);
	return ret != NULL;
}

int in_async(void)
{
	if (!main_thread_set)
		return 0; /* no asyncs started yet */
	return !pthread_equal(main_thread, pthread_self());
}

static void NORETURN async_exit(int code)
{
	pthread_exit((void *)(intptr_t)code);
}

#else

static struct {
	void (**handlers)(void);
	size_t nr;
	size_t alloc;
} git_atexit_hdlrs;

static int git_atexit_installed;

static void git_atexit_dispatch(void)
{
	size_t i;

	for (i=git_atexit_hdlrs.nr ; i ; i--)
		git_atexit_hdlrs.handlers[i-1]();
}

static void git_atexit_clear(void)
{
	free(git_atexit_hdlrs.handlers);
	memset(&git_atexit_hdlrs, 0, sizeof(git_atexit_hdlrs));
	git_atexit_installed = 0;
}

#undef atexit
int git_atexit(void (*handler)(void))
{
	ALLOC_GROW(git_atexit_hdlrs.handlers, git_atexit_hdlrs.nr + 1, git_atexit_hdlrs.alloc);
	git_atexit_hdlrs.handlers[git_atexit_hdlrs.nr++] = handler;
	if (!git_atexit_installed) {
		if (atexit(&git_atexit_dispatch))
			return -1;
		git_atexit_installed = 1;
	}
	return 0;
}
#define atexit git_atexit

static int process_is_async;
int in_async(void)
{
	return process_is_async;
}

static void NORETURN async_exit(int code)
{
	exit(code);
}

#endif

void check_pipe(int err)
{
	if (err == EPIPE) {
		if (in_async())
			async_exit(141);

		signal(SIGPIPE, SIG_DFL);
		raise(SIGPIPE);
		/* Should never happen, but just in case... */
		exit(141);
	}
}

int start_async(struct async *async)
{
	int need_in, need_out;
	int fdin[2], fdout[2];
	int proc_in, proc_out;

	need_in = async->in < 0;
	if (need_in) {
		if (pipe(fdin) < 0) {
			if (async->out > 0)
				close(async->out);
			return error_errno("cannot create pipe");
		}
		async->in = fdin[1];
	}

	need_out = async->out < 0;
	if (need_out) {
		if (pipe(fdout) < 0) {
			if (need_in)
				close_pair(fdin);
			else if (async->in)
				close(async->in);
			return error_errno("cannot create pipe");
		}
		async->out = fdout[0];
	}

	if (need_in)
		proc_in = fdin[0];
	else if (async->in)
		proc_in = async->in;
	else
		proc_in = -1;

	if (need_out)
		proc_out = fdout[1];
	else if (async->out)
		proc_out = async->out;
	else
		proc_out = -1;

#ifdef NO_PTHREADS
	/* Flush stdio before fork() to avoid cloning buffers */
	fflush(NULL);

	async->pid = fork();
	if (async->pid < 0) {
		error_errno("fork (async) failed");
		goto error;
	}
	if (!async->pid) {
		if (need_in)
			close(fdin[1]);
		if (need_out)
			close(fdout[0]);
		git_atexit_clear();
		process_is_async = 1;
		exit(!!async->proc(proc_in, proc_out, async->data));
	}

	mark_child_for_cleanup(async->pid, NULL);

	if (need_in)
		close(fdin[0]);
	else if (async->in)
		close(async->in);

	if (need_out)
		close(fdout[1]);
	else if (async->out)
		close(async->out);
#else
	if (!main_thread_set) {
		/*
		 * We assume that the first time that start_async is called
		 * it is from the main thread.
		 */
		main_thread_set = 1;
		main_thread = pthread_self();
		pthread_key_create(&async_key, NULL);
		pthread_key_create(&async_die_counter, NULL);
		set_die_routine(die_async);
		set_die_is_recursing_routine(async_die_is_recursing);
	}

	if (proc_in >= 0)
		set_cloexec(proc_in);
	if (proc_out >= 0)
		set_cloexec(proc_out);
	async->proc_in = proc_in;
	async->proc_out = proc_out;
	{
		int err = pthread_create(&async->tid, NULL, run_thread, async);
		if (err) {
			error_errno("cannot create thread");
			goto error;
		}
	}
#endif
	return 0;

error:
	if (need_in)
		close_pair(fdin);
	else if (async->in)
		close(async->in);

	if (need_out)
		close_pair(fdout);
	else if (async->out)
		close(async->out);
	return -1;
}

int finish_async(struct async *async)
{
#ifdef NO_PTHREADS
	return wait_or_whine(async->pid, "child process", 0);
#else
	void *ret = (void *)(intptr_t)(-1);

	if (pthread_join(async->tid, &ret))
		error("pthread_join failed");
	return (int)(intptr_t)ret;
#endif
}

const char *find_hook(const char *name)
{
	static struct strbuf path = STRBUF_INIT;

	strbuf_reset(&path);
	strbuf_git_path(&path, "hooks/%s", name);
	if (access(path.buf, X_OK) < 0) {
#ifdef STRIP_EXTENSION
		strbuf_addstr(&path, STRIP_EXTENSION);
		if (access(path.buf, X_OK) >= 0)
			return path.buf;
#endif
		return NULL;
	}
	return path.buf;
}

int run_hook_ve(const char *const *env, const char *name, va_list args)
{
	struct child_process hook = CHILD_PROCESS_INIT;
	const char *p;

	p = find_hook(name);
	if (!p)
		return 0;

	argv_array_push(&hook.args, p);
	while ((p = va_arg(args, const char *)))
		argv_array_push(&hook.args, p);
	hook.env = env;
	hook.no_stdin = 1;
	hook.stdout_to_stderr = 1;

	return run_command(&hook);
}

int run_hook_le(const char *const *env, const char *name, ...)
{
	va_list args;
	int ret;

	va_start(args, name);
	ret = run_hook_ve(env, name, args);
	va_end(args);

	return ret;
}

struct io_pump {
	/* initialized by caller */
	int fd;
	int type; /* POLLOUT or POLLIN */
	union {
		struct {
			const char *buf;
			size_t len;
		} out;
		struct {
			struct strbuf *buf;
			size_t hint;
		} in;
	} u;

	/* returned by pump_io */
	int error; /* 0 for success, otherwise errno */

	/* internal use */
	struct pollfd *pfd;
};

static int pump_io_round(struct io_pump *slots, int nr, struct pollfd *pfd)
{
	int pollsize = 0;
	int i;

	for (i = 0; i < nr; i++) {
		struct io_pump *io = &slots[i];
		if (io->fd < 0)
			continue;
		pfd[pollsize].fd = io->fd;
		pfd[pollsize].events = io->type;
		io->pfd = &pfd[pollsize++];
	}

	if (!pollsize)
		return 0;

	if (poll(pfd, pollsize, -1) < 0) {
		if (errno == EINTR)
			return 1;
		die_errno("poll failed");
	}

	for (i = 0; i < nr; i++) {
		struct io_pump *io = &slots[i];

		if (io->fd < 0)
			continue;

		if (!(io->pfd->revents & (POLLOUT|POLLIN|POLLHUP|POLLERR|POLLNVAL)))
			continue;

		if (io->type == POLLOUT) {
			ssize_t len = xwrite(io->fd,
					     io->u.out.buf, io->u.out.len);
			if (len < 0) {
				io->error = errno;
				close(io->fd);
				io->fd = -1;
			} else {
				io->u.out.buf += len;
				io->u.out.len -= len;
				if (!io->u.out.len) {
					close(io->fd);
					io->fd = -1;
				}
			}
		}

		if (io->type == POLLIN) {
			ssize_t len = strbuf_read_once(io->u.in.buf,
						       io->fd, io->u.in.hint);
			if (len < 0)
				io->error = errno;
			if (len <= 0) {
				close(io->fd);
				io->fd = -1;
			}
		}
	}

	return 1;
}

static int pump_io(struct io_pump *slots, int nr)
{
	struct pollfd *pfd;
	int i;

	for (i = 0; i < nr; i++)
		slots[i].error = 0;

	ALLOC_ARRAY(pfd, nr);
	while (pump_io_round(slots, nr, pfd))
		; /* nothing */
	free(pfd);

	/* There may be multiple errno values, so just pick the first. */
	for (i = 0; i < nr; i++) {
		if (slots[i].error) {
			errno = slots[i].error;
			return -1;
		}
	}
	return 0;
}


int pipe_command(struct child_process *cmd,
		 const char *in, size_t in_len,
		 struct strbuf *out, size_t out_hint,
		 struct strbuf *err, size_t err_hint)
{
	struct io_pump io[3];
	int nr = 0;

	if (in)
		cmd->in = -1;
	if (out)
		cmd->out = -1;
	if (err)
		cmd->err = -1;

	if (start_command(cmd) < 0)
		return -1;

	if (in) {
		io[nr].fd = cmd->in;
		io[nr].type = POLLOUT;
		io[nr].u.out.buf = in;
		io[nr].u.out.len = in_len;
		nr++;
	}
	if (out) {
		io[nr].fd = cmd->out;
		io[nr].type = POLLIN;
		io[nr].u.in.buf = out;
		io[nr].u.in.hint = out_hint;
		nr++;
	}
	if (err) {
		io[nr].fd = cmd->err;
		io[nr].type = POLLIN;
		io[nr].u.in.buf = err;
		io[nr].u.in.hint = err_hint;
		nr++;
	}

	if (pump_io(io, nr) < 0) {
		finish_command(cmd); /* throw away exit code */
		return -1;
	}

	return finish_command(cmd);
}

enum child_state {
	GIT_CP_FREE,
	GIT_CP_WORKING,
	GIT_CP_WAIT_CLEANUP,
};

struct parallel_processes {
	void *data;

	int max_processes;
	int nr_processes;

	get_next_task_fn get_next_task;
	start_failure_fn start_failure;
	task_finished_fn task_finished;

	struct {
		enum child_state state;
		struct child_process process;
		struct strbuf err;
		void *data;
	} *children;
	/*
	 * The struct pollfd is logically part of *children,
	 * but the system call expects it as its own array.
	 */
	struct pollfd *pfd;

	unsigned shutdown : 1;

	int output_owner;
	struct strbuf buffered_output; /* of finished children */
};

static int default_start_failure(struct strbuf *out,
				 void *pp_cb,
				 void *pp_task_cb)
{
	return 0;
}

static int default_task_finished(int result,
				 struct strbuf *out,
				 void *pp_cb,
				 void *pp_task_cb)
{
	return 0;
}

static void kill_children(struct parallel_processes *pp, int signo)
{
	int i, n = pp->max_processes;

	for (i = 0; i < n; i++)
		if (pp->children[i].state == GIT_CP_WORKING)
			kill(pp->children[i].process.pid, signo);
}

static struct parallel_processes *pp_for_signal;

static void handle_children_on_signal(int signo)
{
	kill_children(pp_for_signal, signo);
	sigchain_pop(signo);
	raise(signo);
}

static void pp_init(struct parallel_processes *pp,
		    int n,
		    get_next_task_fn get_next_task,
		    start_failure_fn start_failure,
		    task_finished_fn task_finished,
		    void *data)
{
	int i;

	if (n < 1)
		n = online_cpus();

	pp->max_processes = n;

	trace_printf("run_processes_parallel: preparing to run up to %d tasks", n);

	pp->data = data;
	if (!get_next_task)
		die("BUG: you need to specify a get_next_task function");
	pp->get_next_task = get_next_task;

	pp->start_failure = start_failure ? start_failure : default_start_failure;
	pp->task_finished = task_finished ? task_finished : default_task_finished;

	pp->nr_processes = 0;
	pp->output_owner = 0;
	pp->shutdown = 0;
	pp->children = xcalloc(n, sizeof(*pp->children));
	pp->pfd = xcalloc(n, sizeof(*pp->pfd));
	strbuf_init(&pp->buffered_output, 0);

	for (i = 0; i < n; i++) {
		strbuf_init(&pp->children[i].err, 0);
		child_process_init(&pp->children[i].process);
		pp->pfd[i].events = POLLIN | POLLHUP;
		pp->pfd[i].fd = -1;
	}

	pp_for_signal = pp;
	sigchain_push_common(handle_children_on_signal);
}

static void pp_cleanup(struct parallel_processes *pp)
{
	int i;

	trace_printf("run_processes_parallel: done");
	for (i = 0; i < pp->max_processes; i++) {
		strbuf_release(&pp->children[i].err);
		child_process_clear(&pp->children[i].process);
	}

	free(pp->children);
	free(pp->pfd);

	/*
	 * When get_next_task added messages to the buffer in its last
	 * iteration, the buffered output is non empty.
	 */
	strbuf_write(&pp->buffered_output, stderr);
	strbuf_release(&pp->buffered_output);

	sigchain_pop_common();
}

/* returns
 *  0 if a new task was started.
 *  1 if no new jobs was started (get_next_task ran out of work, non critical
 *    problem with starting a new command)
 * <0 no new job was started, user wishes to shutdown early. Use negative code
 *    to signal the children.
 */
static int pp_start_one(struct parallel_processes *pp)
{
	int i, code;

	for (i = 0; i < pp->max_processes; i++)
		if (pp->children[i].state == GIT_CP_FREE)
			break;
	if (i == pp->max_processes)
		die("BUG: bookkeeping is hard");

	code = pp->get_next_task(&pp->children[i].process,
				 &pp->children[i].err,
				 pp->data,
				 &pp->children[i].data);
	if (!code) {
		strbuf_addbuf(&pp->buffered_output, &pp->children[i].err);
		strbuf_reset(&pp->children[i].err);
		return 1;
	}
	pp->children[i].process.err = -1;
	pp->children[i].process.stdout_to_stderr = 1;
	pp->children[i].process.no_stdin = 1;

	if (start_command(&pp->children[i].process)) {
		code = pp->start_failure(&pp->children[i].err,
					 pp->data,
					 pp->children[i].data);
		strbuf_addbuf(&pp->buffered_output, &pp->children[i].err);
		strbuf_reset(&pp->children[i].err);
		if (code)
			pp->shutdown = 1;
		return code;
	}

	pp->nr_processes++;
	pp->children[i].state = GIT_CP_WORKING;
	pp->pfd[i].fd = pp->children[i].process.err;
	return 0;
}

static void pp_buffer_stderr(struct parallel_processes *pp, int output_timeout)
{
	int i;

	while ((i = poll(pp->pfd, pp->max_processes, output_timeout)) < 0) {
		if (errno == EINTR)
			continue;
		pp_cleanup(pp);
		die_errno("poll");
	}

	/* Buffer output from all pipes. */
	for (i = 0; i < pp->max_processes; i++) {
		if (pp->children[i].state == GIT_CP_WORKING &&
		    pp->pfd[i].revents & (POLLIN | POLLHUP)) {
			int n = strbuf_read_once(&pp->children[i].err,
						 pp->children[i].process.err, 0);
			if (n == 0) {
				close(pp->children[i].process.err);
				pp->children[i].state = GIT_CP_WAIT_CLEANUP;
			} else if (n < 0)
				if (errno != EAGAIN)
					die_errno("read");
		}
	}
}

static void pp_output(struct parallel_processes *pp)
{
	int i = pp->output_owner;
	if (pp->children[i].state == GIT_CP_WORKING &&
	    pp->children[i].err.len) {
		strbuf_write(&pp->children[i].err, stderr);
		strbuf_reset(&pp->children[i].err);
	}
}

static int pp_collect_finished(struct parallel_processes *pp)
{
	int i, code;
	int n = pp->max_processes;
	int result = 0;

	while (pp->nr_processes > 0) {
		for (i = 0; i < pp->max_processes; i++)
			if (pp->children[i].state == GIT_CP_WAIT_CLEANUP)
				break;
		if (i == pp->max_processes)
			break;

		code = finish_command(&pp->children[i].process);

		code = pp->task_finished(code,
					 &pp->children[i].err, pp->data,
					 pp->children[i].data);

		if (code)
			result = code;
		if (code < 0)
			break;

		pp->nr_processes--;
		pp->children[i].state = GIT_CP_FREE;
		pp->pfd[i].fd = -1;
		child_process_init(&pp->children[i].process);

		if (i != pp->output_owner) {
			strbuf_addbuf(&pp->buffered_output, &pp->children[i].err);
			strbuf_reset(&pp->children[i].err);
		} else {
			strbuf_write(&pp->children[i].err, stderr);
			strbuf_reset(&pp->children[i].err);

			/* Output all other finished child processes */
			strbuf_write(&pp->buffered_output, stderr);
			strbuf_reset(&pp->buffered_output);

			/*
			 * Pick next process to output live.
			 * NEEDSWORK:
			 * For now we pick it randomly by doing a round
			 * robin. Later we may want to pick the one with
			 * the most output or the longest or shortest
			 * running process time.
			 */
			for (i = 0; i < n; i++)
				if (pp->children[(pp->output_owner + i) % n].state == GIT_CP_WORKING)
					break;
			pp->output_owner = (pp->output_owner + i) % n;
		}
	}
	return result;
}

int run_processes_parallel(int n,
			   get_next_task_fn get_next_task,
			   start_failure_fn start_failure,
			   task_finished_fn task_finished,
			   void *pp_cb)
{
	int i, code;
	int output_timeout = 100;
	int spawn_cap = 4;
	struct parallel_processes pp;

	pp_init(&pp, n, get_next_task, start_failure, task_finished, pp_cb);
	while (1) {
		for (i = 0;
		    i < spawn_cap && !pp.shutdown &&
		    pp.nr_processes < pp.max_processes;
		    i++) {
			code = pp_start_one(&pp);
			if (!code)
				continue;
			if (code < 0) {
				pp.shutdown = 1;
				kill_children(&pp, -code);
			}
			break;
		}
		if (!pp.nr_processes)
			break;
		pp_buffer_stderr(&pp, output_timeout);
		pp_output(&pp);
		code = pp_collect_finished(&pp);
		if (code) {
			pp.shutdown = 1;
			if (code < 0)
				kill_children(&pp, -code);
		}
	}

	pp_cleanup(&pp);
	return 0;
}