repack: do not accidentally pack kept objects by default

diff --git a/builtin/gc.c b/builtin/gc.c
index 6be6c8d65b26c9149aac2b6c1de6e3217c6ceea7..891a2c2ecb046dc29b2d9ce8b9d2982084bf9b19 100644 (file)
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -167,19 +167,78 @@ static int need_to_gc(void)
        return 1;
 }
 
+/* return NULL on success, else hostname running the gc */
+static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
+{
+       static struct lock_file lock;
+       static char locking_host[128];
+       char my_host[128];
+       struct strbuf sb = STRBUF_INIT;
+       struct stat st;
+       uintmax_t pid;
+       FILE *fp;
+       int fd, should_exit;
+
+       if (gethostname(my_host, sizeof(my_host)))
+               strcpy(my_host, "unknown");
+
+       fd = hold_lock_file_for_update(&lock, git_path("gc.pid"),
+                                      LOCK_DIE_ON_ERROR);
+       if (!force) {
+               fp = fopen(git_path("gc.pid"), "r");
+               memset(locking_host, 0, sizeof(locking_host));
+               should_exit =
+                       fp != NULL &&
+                       !fstat(fileno(fp), &st) &&
+                       /*
+                        * 12 hour limit is very generous as gc should
+                        * never take that long. On the other hand we
+                        * don't really need a strict limit here,
+                        * running gc --auto one day late is not a big
+                        * problem. --force can be used in manual gc
+                        * after the user verifies that no gc is
+                        * running.
+                        */
+                       time(NULL) - st.st_mtime <= 12 * 3600 &&
+                       fscanf(fp, "%"PRIuMAX" %127c", &pid, locking_host) == 2 &&
+                       /* be gentle to concurrent "gc" on remote hosts */
+                       (strcmp(locking_host, my_host) || !kill(pid, 0));
+               if (fp != NULL)
+                       fclose(fp);
+               if (should_exit) {
+                       if (fd >= 0)
+                               rollback_lock_file(&lock);
+                       *ret_pid = pid;
+                       return locking_host;
+               }
+       }
+
+       strbuf_addf(&sb, "%"PRIuMAX" %s",
+                   (uintmax_t) getpid(), my_host);
+       write_in_full(fd, sb.buf, sb.len);
+       strbuf_release(&sb);
+       commit_lock_file(&lock);
+
+       return NULL;
+}
+
 int cmd_gc(int argc, const char **argv, const char *prefix)
 {
        int aggressive = 0;
        int auto_gc = 0;
        int quiet = 0;
+       int force = 0;
+       const char *name;
+       pid_t pid;
 
        struct option builtin_gc_options[] = {
                OPT__QUIET(&quiet, N_("suppress progress reporting")),
                { OPTION_STRING, 0, "prune", &prune_expire, N_("date"),
                        N_("prune unreferenced objects"),
                        PARSE_OPT_OPTARG, NULL, (intptr_t)prune_expire },
-               OPT_BOOLEAN(0, "aggressive", &aggressive, N_("be more thorough (increased runtime)")),
-               OPT_BOOLEAN(0, "auto", &auto_gc, N_("enable auto-gc mode")),
+               OPT_BOOL(0, "aggressive", &aggressive, N_("be more thorough (increased runtime)")),
+               OPT_BOOL(0, "auto", &auto_gc, N_("enable auto-gc mode")),
+               OPT_BOOL(0, "force", &force, N_("force running gc even if there may be another gc running")),
                OPT_END()
        };
 
@@ -225,6 +284,14 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
        } else
                add_repack_all_option();
 
+       name = lock_repo_for_gc(force, &pid);
+       if (name) {
+               if (auto_gc)
+                       return 0; /* be quiet on --auto */
+               die(_("gc is already running on machine '%s' pid %"PRIuMAX" (use --force if not)"),
+                   name, (uintmax_t)pid);
+       }
+
        if (pack_refs && run_command_v_opt(pack_refs_cmd.argv, RUN_GIT_CMD))
                return error(FAILED_RUN, pack_refs_cmd.argv[0]);