[PATCH v3 1/2] run-command: add new check_command helper

[Felipe Contreras <felipe.contreras@xxxxxxxxx>]

And to recover the information from the last run when running
wait_or_whine().

Signed-off-by: Felipe Contreras <felipe.contreras@xxxxxxxxx>
---
 run-command.c | 46 ++++++++++++++++++++++++++++++++++++++++------
 run-command.h |  5 +++++
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/run-command.c b/run-command.c
index 07e27ff..5cb5114 100644
--- a/run-command.c
+++ b/run-command.c
@@ -226,14 +226,20 @@ 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(struct child_process *cmd, pid_t pid, const char *argv0)
 {
 	int status, code = -1;
 	pid_t waiting;
 	int failed_errno = 0;
 
-	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
-		;	/* nothing */
+	/* First try the last status from check_command() */
+	if (cmd && cmd->last_status.valid) {
+		status = cmd->last_status.status;
+		waiting = pid;
+	} else {
+		while ((waiting = waitpid(pid, status, 0)) < 0 && errno == EINTR)
+			;	/* nothing */
+	}
 
 	if (waiting < 0) {
 		failed_errno = errno;
@@ -276,6 +282,8 @@ int start_command(struct child_process *cmd)
 	int failed_errno = failed_errno;
 	char *str;
 
+	cmd->last_status.valid = 0;
+
 	/*
 	 * In case of errors we must keep the promise to close FDs
 	 * that have been passed in via ->in and ->out.
@@ -437,7 +445,7 @@ 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, cmd->pid, cmd->argv[0]);
 		failed_errno = errno;
 		cmd->pid = -1;
 	}
@@ -542,7 +550,7 @@ fail_pipe:
 
 int finish_command(struct child_process *cmd)
 {
-	return wait_or_whine(cmd->pid, cmd->argv[0]);
+	return wait_or_whine(cmd, cmd->pid, cmd->argv[0]);
 }
 
 int run_command(struct child_process *cmd)
@@ -553,6 +561,32 @@ int run_command(struct child_process *cmd)
 	return finish_command(cmd);
 }
 
+int check_command(struct child_process *cmd)
+{
+	int status;
+	pid_t waiting;
+
+	if (cmd->last_status.valid)
+		return 0;
+
+	while ((waiting = waitpid(cmd->pid, &status, WNOHANG)) < 0 && errno == EINTR)
+		; /* nothing */
+
+	if (!waiting)
+		return 1;
+
+	if (waiting == cmd->pid) {
+		cmd->last_status.valid = 1;
+		cmd->last_status.status = status;
+		return 0;
+	}
+
+	if (waiting > 0)
+		die("BUG: waitpid reported a random pid?");
+
+	return 0;
+}
+
 static void prepare_run_command_v_opt(struct child_process *cmd,
 				      const char **argv,
 				      int opt)
@@ -729,7 +763,7 @@ error:
 int finish_async(struct async *async)
 {
 #ifdef NO_PTHREADS
-	return wait_or_whine(async->pid, "child process");
+	return wait_or_whine(NULL, async->pid, "child process");
 #else
 	void *ret = (void *)(intptr_t)(-1);
 
diff --git a/run-command.h b/run-command.h
index 221ce33..74a733d 100644
--- a/run-command.h
+++ b/run-command.h
@@ -39,11 +39,16 @@ struct child_process {
 	unsigned stdout_to_stderr:1;
 	unsigned use_shell:1;
 	unsigned clean_on_exit:1;
+	struct last_status {
+		unsigned valid:1;
+		int status;
+	} last_status;
 };
 
 int start_command(struct child_process *);
 int finish_command(struct child_process *);
 int run_command(struct child_process *);
+int check_command(struct child_process *);
 
 extern char *find_hook(const char *name);
 extern int run_hook(const char *index_file, const char *name, ...);
-- 
1.8.2

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