gvfs-helper-client: clean up server process(es)

On Linux, the following command would cause the terminal to be stuck
waiting:

  git fetch origin foobar

The issue would be that the fetch would fail with the error

  fatal: couldn't find remote ref foobar

but the underlying git-gvfs-helper process wouldn't die. The
`subprocess_exit_handler()` method would close its stdin and stdout, but
that wouldn't be enough to cause the process to end, even though the
`packet_read_line_gently()` call that is run in `do_sub_cmd__server()`
in a loop should return -1 and the process should the terminate
peacefully.

While it is unclear why this does not happen, there may be other
conditions where the `gvfs-helper` process would not terminate. Let's
ensure that the gvfs-helper-client process cleans up the gvfs-helper
server processes that it spawned upon exit.

Reported-by: Stuart Wilcox Humilde <stuartwilcox@microsoft.com>
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: derrickstolee

git.c

@@ -2,6 +2,7 @@
 
 #include "builtin.h"
 #include "gvfs.h"
+#include "gvfs-helper-client.h"
 #include "config.h"
 #include "environment.h"
 #include "exec-cmd.h"
@@ -982,6 +983,7 @@ int cmd_main(int argc, const char **argv)
 
 	trace_command_performance(argv);
 	atexit(post_command_hook_atexit);
+	atexit(stop_gh_server_subprocesses);
 
 	/*
 	 * "git-xxxx" is the same as "git xxxx", but we obviously:

gvfs-helper-client.c

@@ -38,6 +38,42 @@ static struct object_directory *gh_client__chosen_odb;
 #define CAP_OBJECTS__VERB_POST_NAME "post"
 #define CAP_OBJECTS__VERB_PREFETCH_NAME "prefetch"
 
+void stop_gh_server_subprocesses(void)
+{
+	struct gh_server__process *entry, **entries;
+	struct hashmap_iter iter;
+	size_t i = 0, size;
+
+	if (!gh_server__subprocess_map_initialized)
+		return;
+
+	/*
+	 * Since `subprocess_stop()` modifies the hashmap by removing the
+	 * respective subprocess, we cannot use `hashmap_for_each_entry()`
+	 * directly, but have to copy the entries to an array first.
+	 */
+	size = hashmap_get_size(&gh_server__subprocess_map);
+	ALLOC_ARRAY(entries, size);
+	hashmap_for_each_entry(&gh_server__subprocess_map,
+			       &iter, entry, subprocess)
+		entries[i++] = entry;
+	if (i != size)
+		BUG("gh_server__subprocess_map: size mismatch: "
+		    "%"PRIuMAX" != %"PRIuMAX,
+		      (uintmax_t)i, (uintmax_t)size);
+	while(i--) {
+		subprocess_stop(&gh_server__subprocess_map,
+				&entries[i]->subprocess);
+		FREE_AND_NULL(entries[i]);
+	}
+
+	FREE_AND_NULL(entries);
+
+	hashmap_clear_and_free(&gh_server__subprocess_map,
+			       struct gh_server__process, subprocess);
+	gh_server__subprocess_map_initialized = 0;
+}
+
 static int gh_client__start_fn(struct subprocess_entry *subprocess)
 {
 	static int versions[] = {1, 0};

gvfs-helper-client.h

@@ -84,4 +84,9 @@ int gh_client__drain_queue(enum gh_client__created *p_ghc);
 int gh_client__prefetch(timestamp_t seconds_since_epoch,
 			int *nr_packfiles_received);
 
+/*
+ * Clean up long-running processes at and of the Git process.
+ */
+void stop_gh_server_subprocesses(void);
+
 #endif /* GVFS_HELPER_CLIENT_H */