lua+js: Implement utils.getpid()

Usable for uniquely identifying mpv instances from
subprocesses, controlling mpv with AppleScript, ...

Adds a new mp_getpid() wrapper for cross-platform reasons.

DOCS/man/javascript.rst

@@ -180,6 +180,8 @@ Otherwise, where the Lua APIs return ``nil`` on error, JS returns ``undefined``.
 
 ``mp.utils.subprocess_detached(t)``
 
+``mp.utils.getpid()`` (LE)
+
 ``mp.add_hook(type, priority, fn)``
 
 Additional utilities

DOCS/man/lua.rst

@@ -682,6 +682,10 @@ strictly part of the guaranteed API.
 
     The function returns ``nil``.
 
+``utils.getpid()``
+    Returns the process ID of the running mpv process. This can be used to identify
+    the calling mpv when launching (detached) subprocesses.
+
 ``utils.parse_json(str [, trail])``
     Parses the given string argument as JSON, and returns it as a Lua table. On
     error, returns ``nil, error``. (Currently, ``error`` is just a string

osdep/getpid.h

@@ -0,0 +1,29 @@
+/*
+ * getpid wrapper
+ *
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#ifdef _WIN32
+#include <windows.h>
+#define mp_getpid() GetCurrentProcessId()
+#else // POSIX
+#include <sys/types.h>
+#include <unistd.h>
+#define mp_getpid() getpid()
+#endif

player/javascript.c

@@ -40,6 +40,7 @@
 #include "osdep/subprocess.h"
 #include "osdep/timer.h"
 #include "osdep/threads.h"
+#include "osdep/getpid.h"
 #include "stream/stream.h"
 #include "sub/osd.h"
 #include "core.h"
@@ -990,6 +991,12 @@ static void script_subprocess_detached(js_State *J, void *af)
     af_subprocess_common(J, 1, af);
 }
 
+// args: none
+static void script_getpid(js_State *J)
+{
+    js_pushnumber(J, mp_getpid());
+}
+
 // args: prefixed file name, data (c-str)
 static void script_write_file(js_State *J, void *af)
 {
@@ -1296,6 +1303,7 @@ static const struct fn_entry utils_fns[] = {
     AF_ENTRY(get_user_path, 1),
     AF_ENTRY(subprocess, 1),
     AF_ENTRY(subprocess_detached, 1),
+    FN_ENTRY(getpid, 0),
 
     FN_ENTRY(read_file, 2),
     AF_ENTRY(write_file, 2),

player/lua.c

@@ -44,6 +44,7 @@
 #include "osdep/subprocess.h"
 #include "osdep/timer.h"
 #include "osdep/threads.h"
+#include "osdep/getpid.h"
 #include "stream/stream.h"
 #include "sub/osd.h"
 #include "core.h"
@@ -1252,6 +1253,12 @@ static int script_subprocess_detached(lua_State *L)
     return 1;
 }
 
+static int script_getpid(lua_State *L)
+{
+    lua_pushnumber(L, mp_getpid());
+    return 1;
+}
+
 static int script_parse_json(lua_State *L)
 {
     mp_lua_optarg(L, 2);
@@ -1338,6 +1345,7 @@ static const struct fn_entry utils_fns[] = {
     FN_ENTRY(join_path),
     FN_ENTRY(subprocess),
     FN_ENTRY(subprocess_detached),
+    FN_ENTRY(getpid),
     FN_ENTRY(parse_json),
     FN_ENTRY(format_json),
     {0}