Create a new sub-process module that can be used to reduce the cost of
starting up a sub-process for multiple commands. It does this by
keeping the external process running and processing all commands by
communicating over standard input and standard output using the packet
format (pkt-line) based protocol. Full documentation is contained in
Documentation/technical/api-sub-process.txt.
This code is refactored from:
Commit edcc85814c ("convert: add filter.<driver>.process option", 2016-10-16)
keeps the external process running and processes all commands
Signed-off-by: Ben Peart <benpeart@xxxxxxxxxxxxx>
---
Documentation/technical/api-sub-process.txt | 55 ++++++++++++++
Makefile | 1 +
sub-process.c | 113 ++++++++++++++++++++++++++++
sub-process.h | 46 +++++++++++
4 files changed, 215 insertions(+)
create mode 100644 Documentation/technical/api-sub-process.txt
create mode 100644 sub-process.c
create mode 100644 sub-process.h
diff --git a/Documentation/technical/api-sub-process.txt b/Documentation/technical/api-sub-process.txt
new file mode 100644
index 0000000000..8471875611
--- /dev/null
+++ b/Documentation/technical/api-sub-process.txt
@@ -0,0 +1,55 @@
+sub-process API
+===============
+
+The sub-process API makes it possible to run background sub-processes
+that should run until the git command exits and communicate with it
+through stdin and stdout. This reduces the overhead of having to fork
+a new process each time it needs to be communicated with.
+
+The sub-processes are kept in a hashmap by command name and looked up
+via the subprocess_find_entry function. If an existing instance can not
+be found then a new process should be created and started. When the
+parent git command terminates, all sub-processes are also terminated.
+
+This API is based on the run-command API.
+
+Data structures
+---------------
+
+* `struct subprocess_entry`
+
+The sub-process structure. Members should not be accessed directly.
+
+Types
+-----
+
+'int(*subprocess_start_fn)(struct subprocess_entry *entry)'::
+
+ User-supplied function to initialize the sub-process. This is
+ typically used to negoiate the interface version and capabilities.
+
+
+Functions
+---------
+
+`subprocess_start`::
+
+ Start a subprocess and add it to the subprocess hashmap.
+
+`subprocess_stop`::
+
+ Kill a subprocess and remove it from the subprocess hashmap.
+
+`subprocess_find_entry`::
+
+ Find a subprocess in the subprocess hashmap.
+
+`subprocess_get_child_process`::
+
+ Get the underlying `struct child_process` from a subprocess.
+
+`subprocess_read_status`::
+
+ Helper function to read packets looking for the last "status=<foo>"
+ key/value pair.
+
diff --git a/Makefile b/Makefile
index a5a11e721a..8afe733092 100644
--- a/Makefile
+++ b/Makefile
@@ -830,6 +830,7 @@ LIB_OBJS += streaming.o
LIB_OBJS += string-list.o
LIB_OBJS += submodule.o
LIB_OBJS += submodule-config.o
+LIB_OBJS += sub-process.o
LIB_OBJS += symlinks.o
LIB_OBJS += tag.o
LIB_OBJS += tempfile.o
diff --git a/sub-process.c b/sub-process.c
new file mode 100644
index 0000000000..02050b6867
--- /dev/null
+++ b/sub-process.c
@@ -0,0 +1,113 @@
+/*
+ * Generic implementation of background process infrastructure.
+ */
+#include "sub-process.h"
+#include "sigchain.h"
+#include "pkt-line.h"
+
+static int subprocess_map_initialized;
+static struct hashmap subprocess_map;
+
+static int name2process_cmp(const struct subprocess_entry *e1,
+ const struct subprocess_entry *e2, const void *unused)
+{
+ return strcmp(e1->cmd, e2->cmd);
+}
+
+static void subprocess_exit_handler(struct child_process *process)
+{
+ sigchain_push(SIGPIPE, SIG_IGN);
+ /* Closing the pipe signals the filter to initiate a shutdown. */
+ close(process->in);
+ close(process->out);
+ sigchain_pop(SIGPIPE);
+ /* Finish command will wait until the shutdown is complete. */
+ finish_command(process);
+}
+
+int subprocess_start(struct subprocess_entry *entry, const char *cmd,
+ subprocess_start_fn startfn)
+{
+ int err;
+ const char *argv[] = { cmd, NULL };
+
+ if (!subprocess_map_initialized) {
+ hashmap_init(&subprocess_map, (hashmap_cmp_fn)name2process_cmp, 0);
+ subprocess_map_initialized = 1;
+ }
+
+ entry->cmd = cmd;
+
+ child_process_init(&entry->process);
+ entry->process.argv = argv;
+ entry->process.use_shell = 1;
+ entry->process.in = -1;
+ entry->process.out = -1;
+ entry->process.clean_on_exit = 1;
+ entry->process.clean_on_exit_handler = subprocess_exit_handler;
+
+ err = start_command(&entry->process);
+ if (err) {
+ error("cannot fork to run sub-process '%s'", entry->cmd);
+ return err;
+ }
+
+ err = startfn(entry);
+ if (err) {
+ error("initialization for sub-process '%s' failed", entry->cmd);
+ subprocess_stop(entry);
+ return err;
+ }
+
+ hashmap_entry_init(entry, strhash(entry->cmd));
+ hashmap_add(&subprocess_map, entry);
+
+ return 0;
+}
+
+void subprocess_stop(struct subprocess_entry *entry)
+{
+ if (!entry)
+ return;
+
+ entry->process.clean_on_exit = 0;
+ kill(entry->process.pid, SIGTERM);
+ finish_command(&entry->process);
+
+ hashmap_remove(&subprocess_map, entry, NULL);
+}
+
+struct subprocess_entry *subprocess_find_entry(const char *cmd)
+{
+ struct subprocess_entry key;
+
+ if (!subprocess_map_initialized) {
+ hashmap_init(&subprocess_map, (hashmap_cmp_fn)name2process_cmp, 0);
+ subprocess_map_initialized = 1;
+ return NULL;
+ }
+
+ hashmap_entry_init(&key, strhash(cmd));
+ key.cmd = cmd;
+ return hashmap_get(&subprocess_map, &key, NULL);
+}
+
+void subprocess_read_status(int fd, struct strbuf *status)
+{
+ struct strbuf **pair;
+ char *line;
+ for (;;) {
+ line = packet_read_line(fd, NULL);
+ if (!line)
+ break;
+ pair = strbuf_split_str(line, '=', 2);
+ if (pair[0] && pair[0]->len && pair[1]) {
+ /* the last "status=<foo>" line wins */
+ if (!strcmp(pair[0]->buf, "status=")) {
+ strbuf_reset(status);
+ strbuf_addbuf(status, pair[1]);
+ }
+ }
+ strbuf_list_free(pair);
+ }
+}
diff --git a/sub-process.h b/sub-process.h
new file mode 100644
index 0000000000..235f1e5fa3
--- /dev/null
+++ b/sub-process.h
@@ -0,0 +1,46 @@
+#ifndef SUBPROCESS_H
+#define SUBPROCESS_H
+
+#include "git-compat-util.h"
+#include "hashmap.h"
+#include "run-command.h"
+
+/*
+ * Generic implementation of background process infrastructure.
+ * See Documentation/technical/api-background-process.txt.
+ */
+
+ /* data structures */
+
+struct subprocess_entry {
+ struct hashmap_entry ent; /* must be the first member! */
+ struct child_process process;
+ const char *cmd;
+};
+
+/* subprocess functions */
+
+typedef int(*subprocess_start_fn)(struct subprocess_entry *entry);
+int subprocess_start(struct subprocess_entry *entry, const char *cmd,
+ subprocess_start_fn startfn);
+
+void subprocess_stop(struct subprocess_entry *entry);
+
+struct subprocess_entry *subprocess_find_entry(const char *cmd);
+
+/* subprocess helper functions */
+
+static inline struct child_process *subprocess_get_child_process(
+ struct subprocess_entry *entry)
+{
+ return &entry->process;
+}
+
+/*
+ * Helper function that will read packets looking for "status=<foo>"
+ * key/value pairs and return the value from the last "status" packet
+ */
+
+void subprocess_read_status(int fd, struct strbuf *status);
+
+#endif
--
2.12.0.gvfs.1.42.g0b7328eac2