1 files changed, 721 insertions, 131 deletions

diff --git a/run-command.c b/run-command.c
index 3914d9c511..5227f78aea 100644
--- a/run-command.c
+++ b/run-command.c
@@ -3,44 +3,89 @@
 #include "exec_cmd.h"
 #include "sigchain.h"
 #include "argv-array.h"
+#include "thread-utils.h"
+#include "strbuf.h"
 
-#ifndef SHELL_PATH
-# define SHELL_PATH "/bin/sh"
-#endif
+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)
+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);
-		free(p);
+
+		if (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);
+	cleanup_children(sig, 1);
 	sigchain_pop(sig);
 	raise(sig);
 }
 
 static void cleanup_children_on_exit(void)
 {
-	cleanup_children(SIGTERM);
+	cleanup_children(SIGTERM, 0);
 }
 
-static void mark_child_for_cleanup(pid_t pid)
+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;
 
@@ -148,56 +193,46 @@ int sane_execvp(const char *file, char * const argv[])
 	return -1;
 }
 
-static const char **prepare_shell_cmd(const char **argv)
+static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
 {
-	int argc, nargc = 0;
-	const char **nargv;
-
-	for (argc = 0; argv[argc]; argc++)
-		; /* just counting */
-	/* +1 for NULL, +3 for "sh -c" plus extra $0 */
-	nargv = xmalloc(sizeof(*nargv) * (argc + 1 + 3));
-
-	if (argc < 1)
+	if (!argv[0])
 		die("BUG: shell command is empty");
 
 	if (strcspn(argv[0], "|&;<>()$`\\\"' \t\n*?[#~=%") != strlen(argv[0])) {
 #ifndef GIT_WINDOWS_NATIVE
-		nargv[nargc++] = SHELL_PATH;
+		argv_array_push(out, SHELL_PATH);
 #else
-		nargv[nargc++] = "sh";
+		argv_array_push(out, "sh");
 #endif
-		nargv[nargc++] = "-c";
-
-		if (argc < 2)
-			nargv[nargc++] = argv[0];
-		else {
-			struct strbuf arg0 = STRBUF_INIT;
-			strbuf_addf(&arg0, "%s \"$@\"", argv[0]);
-			nargv[nargc++] = strbuf_detach(&arg0, NULL);
-		}
-	}
+		argv_array_push(out, "-c");
 
-	for (argc = 0; argv[argc]; argc++)
-		nargv[nargc++] = argv[argc];
-	nargv[nargc] = NULL;
+		/*
+		 * 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]);
+	}
 
-	return nargv;
+	argv_array_pushv(out, argv);
+	return out->argv;
 }
 
 #ifndef GIT_WINDOWS_NATIVE
 static int execv_shell_cmd(const char **argv)
 {
-	const char **nargv = prepare_shell_cmd(argv);
-	trace_argv_printf(nargv, "trace: exec:");
-	sane_execvp(nargv[0], (char **)nargv);
-	free(nargv);
+	struct argv_array nargv = ARGV_ARRAY_INIT;
+	prepare_shell_cmd(&nargv, argv);
+	trace_argv_printf(nargv.argv, "trace: exec:");
+	sane_execvp(nargv.argv[0], (char **)nargv.argv);
+	argv_array_clear(&nargv);
 	return -1;
 }
 #endif
 
 #ifndef GIT_WINDOWS_NATIVE
-static int child_err = 2;
 static int child_notifier = -1;
 
 static void notify_parent(void)
@@ -209,17 +244,6 @@ static void notify_parent(void)
 	 */
 	xwrite(child_notifier, "", 1);
 }
-
-static NORETURN void die_child(const char *err, va_list params)
-{
-	vwritef(child_err, "fatal: ", err, params);
-	exit(128);
-}
-
-static void error_child(const char *err, va_list params)
-{
-	vwritef(child_err, "error: ", err, params);
-}
 #endif
 
 static inline void set_cloexec(int fd)
@@ -229,7 +253,7 @@ static inline void set_cloexec(int fd)
 		fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
 }
 
-static int wait_or_whine(pid_t pid, const char *argv0)
+static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
 {
 	int status, code = -1;
 	pid_t waiting;
@@ -237,15 +261,17 @@ static int wait_or_whine(pid_t pid, const char *argv0)
 
 	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
 		;	/* nothing */
+	if (in_signal)
+		return 0;
 
 	if (waiting < 0) {
 		failed_errno = errno;
-		error("waitpid for %s failed: %s", argv0, strerror(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)
+		if (code != SIGINT && code != SIGQUIT && code != SIGPIPE)
 			error("%s died of signal %d", argv0, code);
 		/*
 		 * This return value is chosen so that code & 0xff
@@ -279,6 +305,11 @@ int start_command(struct child_process *cmd)
 	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.
@@ -328,6 +359,7 @@ int start_command(struct child_process *cmd)
 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;
 		}
@@ -352,11 +384,10 @@ fail_pipe:
 		 * in subsequent call paths use the parent's stderr.
 		 */
 		if (cmd->no_stderr || need_err) {
-			child_err = dup(2);
+			int child_err = dup(2);
 			set_cloexec(child_err);
+			set_error_handle(fdopen(child_err, "w"));
 		}
-		set_die_routine(die_child);
-		set_error_routine(error_child);
 
 		close(notify_pipe[0]);
 		set_cloexec(notify_pipe[1]);
@@ -422,10 +453,9 @@ fail_pipe:
 		}
 	}
 	if (cmd->pid < 0)
-		error("cannot fork() for %s: %s", cmd->argv[0],
-			strerror(errno));
+		error_errno("cannot fork() for %s", cmd->argv[0]);
 	else if (cmd->clean_on_exit)
-		mark_child_for_cleanup(cmd->pid);
+		mark_child_for_cleanup(cmd->pid, cmd);
 
 	/*
 	 * Wait for child's execvp. If the execvp succeeds (or if fork()
@@ -440,7 +470,7 @@ fail_pipe:
 		 * At this point we know that fork() succeeded, but execvp()
 		 * failed. Errors have been reported to our stderr.
 		 */
-		wait_or_whine(cmd->pid, cmd->argv[0]);
+		wait_or_whine(cmd->pid, cmd->argv[0], 0);
 		failed_errno = errno;
 		cmd->pid = -1;
 	}
@@ -450,7 +480,7 @@ fail_pipe:
 {
 	int fhin = 0, fhout = 1, fherr = 2;
 	const char **sargv = cmd->argv;
-	char **env = environ;
+	struct argv_array nargv = ARGV_ARRAY_INIT;
 
 	if (cmd->no_stdin)
 		fhin = open("/dev/null", O_RDWR);
@@ -475,27 +505,20 @@ fail_pipe:
 	else if (cmd->out > 1)
 		fhout = dup(cmd->out);
 
-	if (cmd->env)
-		env = make_augmented_environ(cmd->env);
-
 	if (cmd->git_cmd)
-		cmd->argv = prepare_git_cmd(cmd->argv);
+		cmd->argv = prepare_git_cmd(&nargv, cmd->argv);
 	else if (cmd->use_shell)
-		cmd->argv = prepare_shell_cmd(cmd->argv);
+		cmd->argv = prepare_shell_cmd(&nargv, cmd->argv);
 
-	cmd->pid = mingw_spawnvpe(cmd->argv[0], cmd->argv, env, cmd->dir,
-				  fhin, fhout, fherr);
+	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("cannot spawn %s: %s", cmd->argv[0], strerror(errno));
+		error_errno("cannot spawn %s", cmd->argv[0]);
 	if (cmd->clean_on_exit && cmd->pid >= 0)
-		mark_child_for_cleanup(cmd->pid);
-
-	if (cmd->env)
-		free_environ(env);
-	if (cmd->git_cmd)
-		free(cmd->argv);
+		mark_child_for_cleanup(cmd->pid, cmd);
 
+	argv_array_clear(&nargv);
 	cmd->argv = sargv;
 	if (fhin != 0)
 		close(fhin);
@@ -519,6 +542,7 @@ fail_pipe:
 			close_pair(fderr);
 		else if (cmd->err)
 			close(cmd->err);
+		child_process_clear(cmd);
 		errno = failed_errno;
 		return -1;
 	}
@@ -543,42 +567,45 @@ fail_pipe:
 
 int finish_command(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid, cmd->argv[0]);
+	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 = start_command(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);
 }
 
-static void prepare_run_command_v_opt(struct child_process *cmd,
-				      const char **argv,
-				      int opt)
-{
-	memset(cmd, 0, sizeof(*cmd));
-	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;
-}
-
 int run_command_v_opt(const char **argv, int opt)
 {
-	struct child_process cmd;
-	prepare_run_command_v_opt(&cmd, argv, opt);
-	return run_command(&cmd);
+	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;
-	prepare_run_command_v_opt(&cmd, argv, opt);
+	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);
@@ -595,6 +622,16 @@ 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;
@@ -604,7 +641,7 @@ static NORETURN void die_async(const char *err, va_list params)
 {
 	vreportf("fatal: ", err, params);
 
-	if (!pthread_equal(main_thread, pthread_self())) {
+	if (in_async()) {
 		struct async *async = pthread_getspecific(async_key);
 		if (async->proc_in >= 0)
 			close(async->proc_in);
@@ -623,8 +660,83 @@ static int async_die_is_recursing(void)
 	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;
@@ -636,7 +748,7 @@ int start_async(struct async *async)
 		if (pipe(fdin) < 0) {
 			if (async->out > 0)
 				close(async->out);
-			return error("cannot create pipe: %s", strerror(errno));
+			return error_errno("cannot create pipe");
 		}
 		async->in = fdin[1];
 	}
@@ -648,7 +760,7 @@ int start_async(struct async *async)
 				close_pair(fdin);
 			else if (async->in)
 				close(async->in);
-			return error("cannot create pipe: %s", strerror(errno));
+			return error_errno("cannot create pipe");
 		}
 		async->out = fdout[0];
 	}
@@ -673,7 +785,7 @@ int start_async(struct async *async)
 
 	async->pid = fork();
 	if (async->pid < 0) {
-		error("fork (async) failed: %s", strerror(errno));
+		error_errno("fork (async) failed");
 		goto error;
 	}
 	if (!async->pid) {
@@ -681,10 +793,12 @@ int start_async(struct async *async)
 			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);
+	mark_child_for_cleanup(async->pid, NULL);
 
 	if (need_in)
 		close(fdin[0]);
@@ -718,7 +832,7 @@ int start_async(struct async *async)
 	{
 		int err = pthread_create(&async->tid, NULL, run_thread, async);
 		if (err) {
-			error("cannot create thread: %s", strerror(err));
+			error_errno("cannot create thread");
 			goto error;
 		}
 	}
@@ -741,7 +855,7 @@ error:
 int finish_async(struct async *async)
 {
 #ifdef NO_PTHREADS
-	return wait_or_whine(async->pid, "child process");
+	return wait_or_whine(async->pid, "child process", 0);
 #else
 	void *ret = (void *)(intptr_t)(-1);
 
@@ -751,47 +865,523 @@ int finish_async(struct async *async)
 #endif
 }
 
-char *find_hook(const char *name)
+const char *find_hook(const char *name)
 {
-	char *path = git_path("hooks/%s", name);
-	if (access(path, X_OK) < 0)
-		path = NULL;
-
-	return path;
+	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(const char *index_file, const char *name, ...)
+int run_hook_ve(const char *const *env, const char *name, va_list args)
 {
-	struct child_process hook;
-	struct argv_array argv = ARGV_ARRAY_INIT;
-	const char *p, *env[2];
-	char index[PATH_MAX];
-	va_list args;
-	int ret;
+	struct child_process hook = CHILD_PROCESS_INIT;
+	const char *p;
 
 	p = find_hook(name);
 	if (!p)
 		return 0;
 
-	argv_array_push(&argv, p);
+	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);
-	while ((p = va_arg(args, const char *)))
-		argv_array_push(&argv, p);
+	ret = run_hook_ve(env, name, args);
 	va_end(args);
 
-	memset(&hook, 0, sizeof(hook));
-	hook.argv = argv.argv;
-	hook.no_stdin = 1;
-	hook.stdout_to_stderr = 1;
-	if (index_file) {
-		snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", index_file);
-		env[0] = index;
-		env[1] = NULL;
-		hook.env = env;
+	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++];
 	}
 
-	ret = run_command(&hook);
-	argv_array_clear(&argv);
-	return ret;
+	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;
 }