From: Johannes Sixt <johannes.sixt@telecom.at>
Date: Fri, 19 Oct 2007 19:48:00 +0000 (+0200)
Subject: Add infrastructure to run a function asynchronously.
X-Git-Tag: v1.5.4-rc0~292^2~6
X-Git-Url: https://git.lorimer.id.au/gitweb.git/diff_plain/2d22c208304156892fd6674e0055a3212c1e2d2e

Add infrastructure to run a function asynchronously.

This adds start_async() and finish_async(), which runs a function
asynchronously. Communication with the caller happens only via pipes.
For this reason, this implementation forks off a child process that runs
the function.

[sp: Style nit fixed by removing unnecessary block on if condition
inside of start_async()]

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

diff --git a/run-command.c b/run-command.c
index d00c03bbdf..d99a6c4ea7 100644
--- a/run-command.c
+++ b/run-command.c
@@ -127,16 +127,11 @@ int start_command(struct child_process *cmd)
 	return 0;
 }
 
-int finish_command(struct child_process *cmd)
+static int wait_or_whine(pid_t pid)
 {
-	if (cmd->close_in)
-		close(cmd->in);
-	if (cmd->close_out)
-		close(cmd->out);
-
 	for (;;) {
 		int status, code;
-		pid_t waiting = waitpid(cmd->pid, &status, 0);
+		pid_t waiting = waitpid(pid, &status, 0);
 
 		if (waiting < 0) {
 			if (errno == EINTR)
@@ -144,7 +139,7 @@ int finish_command(struct child_process *cmd)
 			error("waitpid failed (%s)", strerror(errno));
 			return -ERR_RUN_COMMAND_WAITPID;
 		}
-		if (waiting != cmd->pid)
+		if (waiting != pid)
 			return -ERR_RUN_COMMAND_WAITPID_WRONG_PID;
 		if (WIFSIGNALED(status))
 			return -ERR_RUN_COMMAND_WAITPID_SIGNAL;
@@ -158,6 +153,15 @@ int finish_command(struct child_process *cmd)
 	}
 }
 
+int finish_command(struct child_process *cmd)
+{
+	if (cmd->close_in)
+		close(cmd->in);
+	if (cmd->close_out)
+		close(cmd->out);
+	return wait_or_whine(cmd->pid);
+}
+
 int run_command(struct child_process *cmd)
 {
 	int code = start_command(cmd);
@@ -200,3 +204,34 @@ int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const
 	cmd.env = env;
 	return run_command(&cmd);
 }
+
+int start_async(struct async *async)
+{
+	int pipe_out[2];
+
+	if (pipe(pipe_out) < 0)
+		return error("cannot create pipe: %s", strerror(errno));
+
+	async->pid = fork();
+	if (async->pid < 0) {
+		error("fork (async) failed: %s", strerror(errno));
+		close_pair(pipe_out);
+		return -1;
+	}
+	if (!async->pid) {
+		close(pipe_out[0]);
+		exit(!!async->proc(pipe_out[1], async->data));
+	}
+	async->out = pipe_out[0];
+	close(pipe_out[1]);
+	return 0;
+}
+
+int finish_async(struct async *async)
+{
+	int ret = 0;
+
+	if (wait_or_whine(async->pid))
+		ret = error("waitpid (async) failed");
+	return ret;
+}
diff --git a/run-command.h b/run-command.h
index 35b9fb61f1..94e1e9d516 100644
--- a/run-command.h
+++ b/run-command.h
@@ -43,4 +43,26 @@ int run_command_v_opt_cd(const char **argv, int opt, const char *dir);
  */
 int run_command_v_opt_cd_env(const char **argv, int opt, const char *dir, const char *const *env);
 
+/*
+ * The purpose of the following functions is to feed a pipe by running
+ * a function asynchronously and providing output that the caller reads.
+ *
+ * It is expected that no synchronization and mutual exclusion between
+ * the caller and the feed function is necessary so that the function
+ * can run in a thread without interfering with the caller.
+ */
+struct async {
+	/*
+	 * proc writes to fd and closes it;
+	 * returns 0 on success, non-zero on failure
+	 */
+	int (*proc)(int fd, void *data);
+	void *data;
+	int out;	/* caller reads from here and closes it */
+	pid_t pid;
+};
+
+int start_async(struct async *async);
+int finish_async(struct async *async);
+
 #endif