fix(python-plugin): add uwsgi fork hooks to update internal interpret…

…er state

core/master_utils.c

@@ -747,9 +747,22 @@ int uwsgi_respawn_worker(int wid) {
 		pthread_mutex_lock(&uwsgi.threaded_logger_lock);
 	}
 
+
+	for (i = 0; i < 256; i++) {
+		if (uwsgi.p[i]->pre_uwsgi_fork) {
+			uwsgi.p[i]->pre_uwsgi_fork();
+		}
+	}
+
 	pid_t pid = uwsgi_fork(uwsgi.workers[wid].name);
 
 	if (pid == 0) {
+		for (i = 0; i < 256; i++) {
+			if (uwsgi.p[i]->post_uwsgi_fork) {
+				uwsgi.p[i]->post_uwsgi_fork(1);
+			}
+		}
+
 		signal(SIGWINCH, worker_wakeup);
 		signal(SIGTSTP, worker_wakeup);
 		uwsgi.mywid = wid;
@@ -812,6 +825,12 @@ int uwsgi_respawn_worker(int wid) {
 		uwsgi_error("fork()");
 	}
 	else {
+		for (i = 0; i < 256; i++) {
+			if (uwsgi.p[i]->post_uwsgi_fork) {
+				uwsgi.p[i]->post_uwsgi_fork(0);
+			}
+		}
+
 		// the pid is set only in the master, as the worker should never use it
 		uwsgi.workers[wid].pid = pid;
 

plugins/python/python_plugin.c

@@ -195,6 +195,7 @@ struct uwsgi_option uwsgi_python_options[] = {
 #endif
 
 	{"py-call-osafterfork", no_argument, 0, "enable child processes running cpython to trap OS signals", uwsgi_opt_true, &up.call_osafterfork, 0},
+	{"py-call-uwsgi-fork-hooks", no_argument, 0, "call pre and post hooks when uswgi forks to update the internal interpreter state of CPython", uwsgi_opt_true, &up.call_uwsgi_fork_hooks, 0},
 
 	{"early-python", no_argument, 0, "load the python VM as soon as possible (useful for the fork server)", uwsgi_early_python, NULL, UWSGI_OPT_IMMEDIATE},
 	{"early-pyimport", required_argument, 0, "import a python module in the early phase", uwsgi_early_python_import, NULL, UWSGI_OPT_IMMEDIATE},
@@ -428,12 +429,20 @@ void uwsgi_python_atexit() {
 
 void uwsgi_python_post_fork() {
 
+	// Need to acquire the gil when no master process is used as first worker
+	// will not have been forked like others
+	// Necessary if uwsgi fork hooks called to update interpreter state
+	if (up.call_uwsgi_fork_hooks && !uwsgi.master_process && uwsgi.mywid == 1) {
+		UWSGI_GET_GIL
+	}
+
 	if (uwsgi.i_am_a_spooler) {
 		UWSGI_GET_GIL
 	}	
 
 	// reset python signal flags so child processes can trap signals
-	if (up.call_osafterfork) {
+	// Necessary if uwsgi fork hooks not called to update interpreter state
+	if (!up.call_uwsgi_fork_hooks && up.call_osafterfork) {
 #ifdef HAS_NOT_PyOS_AfterFork_Child
 		PyOS_AfterFork();
 #else
@@ -1129,6 +1138,13 @@ void uwsgi_python_preinit_apps() {
 	up.loaders[LOADER_CALLABLE] = uwsgi_callable_loader;
 	up.loaders[LOADER_STRING_CALLABLE] = uwsgi_string_callable_loader;
 
+	// GIL was released in previous initialization steps but init_pyargv expects
+	// the GIL to be acquired
+	// Necessary if uwsgi fork hooks called to update interpreter state
+	if (up.call_uwsgi_fork_hooks) {
+		UWSGI_GET_GIL
+	}
+
 	init_pyargv();
 
         init_uwsgi_embedded_module();
@@ -1174,12 +1190,19 @@ void uwsgi_python_preinit_apps() {
 		upli = upli->next;
 	}
 
+	// Release the GIL before moving on forward with initialization
+	// Necessary if uwsgi fork hooks called to update interpreter state
+	if (up.call_uwsgi_fork_hooks) {
+		UWSGI_RELEASE_GIL
+	}
+
 }
 
 void uwsgi_python_init_apps() {
 
 	// lazy ?
-	if (uwsgi.mywid > 0) {
+	// Also necessary if uwsgi fork hooks called to update interpreter state
+	if (uwsgi.mywid > 0 || up.call_uwsgi_fork_hooks) {
 		UWSGI_GET_GIL;
 	}
 
@@ -1291,7 +1314,8 @@ void uwsgi_python_init_apps() {
 		}
 	}
 	// lazy ?
-	if (uwsgi.mywid > 0) {
+	// Also necessary if uwsgi fork hooks called to update interpreter state
+	if (uwsgi.mywid > 0 || up.call_uwsgi_fork_hooks) {
 		UWSGI_RELEASE_GIL;
 	}
 
@@ -1304,6 +1328,10 @@ void uwsgi_python_master_fixup(int step) {
 
 	if (!uwsgi.master_process) return;
 
+	// Skip master fixup if uwsgi fork hooks called to update interpreter state
+	if (up.call_uwsgi_fork_hooks)
+		return;
+
 	if (uwsgi.has_threads) {
 		if (step == 0) {
 			if (!master_fixed) {
@@ -1320,6 +1348,40 @@ void uwsgi_python_master_fixup(int step) {
 	}
 }
 
+void uwsgi_python_pre_uwsgi_fork() {
+	if (!up.call_uwsgi_fork_hooks)
+		return;
+
+	if (uwsgi.has_threads) {
+		// Acquire the gil and import lock before forking in order to avoid
+		// deadlocks in workers
+		UWSGI_GET_GIL
+		_PyImport_AcquireLock();
+	}
+}
+
+
+void uwsgi_python_post_uwsgi_fork(int step) {
+	if (!up.call_uwsgi_fork_hooks)
+		return;
+
+	if (uwsgi.has_threads) {
+		if (step == 0) {
+			// Release locks within master process
+			_PyImport_ReleaseLock();
+			UWSGI_RELEASE_GIL
+		}
+		else {
+			// Ensure thread state and locks are cleaned up in child process
+#ifdef HAS_NOT_PyOS_AfterFork_Child
+			PyOS_AfterFork();
+#else
+			PyOS_AfterFork_Child();
+#endif
+		}
+	}
+}
+
 void uwsgi_python_enable_threads() {
 
 #ifdef UWSGI_SHOULD_CALL_PYEVAL_INITTHREADS
@@ -1349,7 +1411,11 @@ void uwsgi_python_enable_threads() {
 		up.reset_ts = threaded_reset_ts;
 	}
 
-
+	// Release the newly created gil from call to PyEval_InitThreads above
+	// Necessary if uwsgi fork hooks called to update interpreter state
+	if (up.call_uwsgi_fork_hooks) {
+		UWSGI_RELEASE_GIL
+	}
 
 	uwsgi_log("python threads support enabled\n");
 
@@ -2044,7 +2110,8 @@ static int uwsgi_python_worker() {
 		return 0;
 	UWSGI_GET_GIL;
 	// ensure signals can be used again from python
-	if (!up.call_osafterfork)
+	// Necessary if fork hooks have been not used to update interpreter state
+	if (!up.call_osafterfork && !up.call_uwsgi_fork_hooks)
 #ifdef HAS_NOT_PyOS_AfterFork_Child
 		PyOS_AfterFork();
 #else
@@ -2130,4 +2197,6 @@ struct uwsgi_plugin python_plugin = {
 
 	.worker = uwsgi_python_worker,
 
+	.pre_uwsgi_fork = uwsgi_python_pre_uwsgi_fork,
+	.post_uwsgi_fork = uwsgi_python_post_uwsgi_fork,
 };

plugins/python/uwsgi_python.h

@@ -1,5 +1,6 @@
 #include <uwsgi.h>
 #include <Python.h>
+#include <pythread.h>
 
 #include <frameobject.h>
 
@@ -238,6 +239,8 @@ struct uwsgi_python {
 	int master_check_signals;
 
 	char *executable;
+
+	int call_uwsgi_fork_hooks;
 };
 
 

tests/deadlocks/master-nothreads.ini

@@ -3,3 +3,4 @@ show-config = true
 master = true
 enable-threads = false
 workers = 1
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/master-singleinterpreter-threads-10workers.ini

@@ -4,3 +4,4 @@ master = true
 enable-threads = true
 workers = 10
 single-interpreter = true
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/master-singleinterpreter-threads-1worker.ini

@@ -4,3 +4,4 @@ master = true
 enable-threads = true
 workers = 1
 single-interpreter = true
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/master-threads-10workers.ini

@@ -3,3 +3,4 @@ show-config = true
 master = true
 enable-threads = true
 workers = 10
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/master-threads-1worker.ini

@@ -3,3 +3,4 @@ show-config = true
 master = true
 enable-threads = true
 workers = 1
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/nomaster-threads-10workers.ini

@@ -3,3 +3,4 @@ show-config = true
 master = false
 enable-threads = true
 workers = 10
+py-call-uwsgi-fork-hooks = true

tests/deadlocks/nomaster-threads-1worker.ini

@@ -3,3 +3,4 @@ show-config = true
 master = false
 enable-threads = true
 workers = 1
+py-call-uwsgi-fork-hooks = true

uwsgi.h

@@ -1095,6 +1095,9 @@ struct uwsgi_plugin {
 	int (*worker)(void);
 
 	void (*early_post_jail) (void);
+
+	void (*pre_uwsgi_fork) (void);
+	void (*post_uwsgi_fork) (int);
 };
 
 #ifdef UWSGI_PCRE