[PATCH 14/15] job-runner: add --daemonize option

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: Apr 3, 2020, 20:48 UTC
Message-ID: <b22398b00443388ece4cd352ac347cd364fc11a3.1585946894.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.597.git.1585946894.gitgitgadget@gmail.com>

From: Derrick Stolee <dstolee@microsoft.com>

Git has the ability to fork the process and launch a "daemonized" copy of the current process. This is used to launch a background 'git gc' command in some cases or to launch the 'git daemon' server process.

Update the 'git job-runner' command with a --daemonize option that launches this background process.

The implementation of daemonize() in setup.c is very clear that this may no-op and return an error if NO_POSIX_GOODIES is not defined. Include an error message to point out that this mechanism may not be available on a platform-by-platform basis.

Include a clear error message that daemonize() might fail due to platform incompatibilities.

I have been running the current version of this series on my Linux VM using --daemonize to keep my copies of torvalds/linux and git/git maintained. Using GIT_TRACE2_PERF set to a path, I can see that the 'git run-job' processes are being created on the correct schedule according to my config for each.

RFC QUESTION: I notice that 'git gc' does not document --daemonize. Is that intentional? Or is it an oversight?

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-job-runner.txt |  5 +++++
 builtin/job-runner.c             | 12 ++++++++++--
 cache.h                          |  4 +---
 daemon.h                         |  7 +++++++
 4 files changed, 23 insertions(+), 5 deletions(-)
 create mode 100644 daemon.h

diff --git a/Documentation/git-job-runner.txt b/Documentation/git-job-runner.txt
index 0719113a008..f48d6bcd10b 100644
--- a/Documentation/git-job-runner.txt
+++ b/Documentation/git-job-runner.txt
@@ -39,6 +39,11 @@ OPTIONS
 	If this is not specified, then the default will be found from
 	`jobs.loopInterval` or the default value of 30 minutes.
 
+--daemonize::
+	If supported by your platform, launch an identical
+	`git job-runner` process in the background and close the
+	foreground process immediately.
+
 
 CONFIGURATION
 -------------
diff --git a/builtin/job-runner.c b/builtin/job-runner.c
index 45f82a50d49..3b629428ef1 100644
--- a/builtin/job-runner.c
+++ b/builtin/job-runner.c
@@ -1,5 +1,6 @@
 #include "builtin.h"
 #include "config.h"
+#include "daemon.h"
 #include "parse-options.h"
 #include "run-command.h"
 #include "string-list.h"
@@ -78,7 +79,8 @@ static int try_get_config(const char *job,
 
 	fclose(proc_out);
 
-	result = finish_command(config_proc);
+	/* ignore result as 'git config' fails on non-existent value */
+	finish_command(config_proc);
 
 cleanup:
 	free(config_proc);
@@ -93,7 +95,7 @@ static int try_get_timestamp(const char *job,
 	char *value;
 	int result = try_get_config(job, repo, postfix, &value);
 
-	if (!result) {
+	if (!result && value) {
 		*t = atol(value);
 		free(value);
 	}
@@ -304,6 +306,7 @@ static int initialize_jobs(struct string_list *list)
 	return 0;
 }
 
+static int arg_daemonize = 0;
 int cmd_job_runner(int argc, const char **argv, const char *prefix)
 {
 	int result;
@@ -316,6 +319,8 @@ int cmd_job_runner(int argc, const char **argv, const char *prefix)
 			       PARSE_OPT_NONEG, arg_repos_append),
 		OPT_INTEGER(0, "interval", &arg_interval,
 			    N_("seconds to pause between running any jobs")),
+		OPT_BOOL(0, "daemonize", &arg_daemonize,
+			 N_("request to spawn a background process")),
 		OPT_END(),
 	};
 
@@ -328,6 +333,9 @@ int cmd_job_runner(int argc, const char **argv, const char *prefix)
 			     builtin_job_runner_usage,
 			     0);
 
+	if (arg_daemonize && daemonize())
+		die(_("failed to daemonize; this may not be available on your platform."));
+
 	result = initialize_jobs(&job_list);
 
 	while (!(result = run_job_loop_step(&job_list))) {
diff --git a/cache.h b/cache.h
index c77b95870a5..34ef690faf6 100644
--- a/cache.h
+++ b/cache.h
@@ -17,6 +17,7 @@
 #include "sha1-array.h"
 #include "repository.h"
 #include "mem-pool.h"
+#include "daemon.h"
 
 #include <zlib.h>
 typedef struct git_zstream {
@@ -631,9 +632,6 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo);
 
-void sanitize_stdfds(void);
-int daemonize(void);
-
 #define alloc_nr(x) (((x)+16)*3/2)
 
 /**
diff --git a/daemon.h b/daemon.h
new file mode 100644
index 00000000000..c1e50a20354
--- /dev/null
+++ b/daemon.h
@@ -0,0 +1,7 @@
+#ifndef DAEMON_H__
+#define DAEMON_H__
+
+void sanitize_stdfds(void);
+int daemonize(void);
+
+#endif

-- 
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