Add support for priority inheritance

Andre Pereira Azevedo Pinto · Andre Pereira Azevedo Pinto · commit f76456b0dc14 · 2019-12-09T14:55:31.000-08:00
Add support for posix mutex priority inheritance. This is important to
avoid priority inversion in systems running with threads with different
priorities.

Signed-off-by: Andre Azevedo &lt;andre.azevedo@gmail.com&gt;
diff --git a/evthread_pthread.c b/evthread_pthread.c
@@ -39,12 +39,13 @@ struct event_base;
 #include "mm-internal.h"
 #include "evthread-internal.h"
 
+static pthread_mutexattr_t attr_default;
 static pthread_mutexattr_t attr_recursive;
 
 static void *
 evthread_posix_lock_alloc(unsigned locktype)
 {
-	pthread_mutexattr_t *attr = NULL;
+	pthread_mutexattr_t *attr = &attr_default;
 	pthread_mutex_t *lock = mm_malloc(sizeof(pthread_mutex_t));
 	if (!lock)
 		return NULL;
@@ -161,7 +162,7 @@ evthread_posix_cond_wait(void *cond_, void *lock_, const struct timeval *tv)
 }
 
 int
-evthread_use_pthreads(void)
+evthread_use_pthreads_with_flags(int flags)
 {
 	struct evthread_lock_callbacks cbs = {
 		EVTHREAD_LOCK_API_VERSION,
@@ -178,14 +179,32 @@ evthread_use_pthreads(void)
 		evthread_posix_cond_signal,
 		evthread_posix_cond_wait
 	};
+
+	if (pthread_mutexattr_init(&attr_default))
+		return -1;
+
 	/* Set ourselves up to get recursive locks. */
 	if (pthread_mutexattr_init(&attr_recursive))
 		return -1;
 	if (pthread_mutexattr_settype(&attr_recursive, PTHREAD_MUTEX_RECURSIVE))
 		return -1;
 
+	if (flags & EVTHREAD_PTHREAD_PRIO_INHERIT) {
+		/* Set up priority inheritance */
+		if (pthread_mutexattr_setprotocol(&attr_default, PTHREAD_PRIO_INHERIT))
+			return -1;
+		if (pthread_mutexattr_setprotocol(&attr_recursive, PTHREAD_PRIO_INHERIT))
+			return -1;
+	}
+
 	evthread_set_lock_callbacks(&cbs);
 	evthread_set_condition_callbacks(&cond_cbs);
 	evthread_set_id_callback(evthread_posix_get_id);
 	return 0;
 }
+
+int
+evthread_use_pthreads(void)
+{
+	return evthread_use_pthreads_with_flags(0);
+}
diff --git a/include/event2/thread.h b/include/event2/thread.h
@@ -212,6 +212,21 @@ int evthread_use_windows_threads(void);
     @return 0 on success, -1 on failure. */
 EVENT2_EXPORT_SYMBOL
 int evthread_use_pthreads(void);
+
+/* Enables posix mutex priority inheritance. */
+#define EVTHREAD_PTHREAD_PRIO_INHERIT 0x01
+
+/**
+ * Sets up Libevent for use with Pthreads locking and thread ID functions.
+ * Use evthred_use_pthreads_with_flags() to use Pthreads locking, taking the
+ * specified flags under consideration.
+ *
+ * @param flags the flags to apply when setting up Pthreads locking. @see EVTHREAD_PTHREAD_*
+ * @return 0 on success, -1 on failure.
+ **/
+EVENT2_EXPORT_SYMBOL
+int evthread_use_pthreads_with_flags(int flags);
+
 /** Defined if Libevent was built with support for evthread_use_pthreads() */
 #define EVTHREAD_USE_PTHREADS_IMPLEMENTED 1
 
diff --git a/test/regress.h b/test/regress.h
@@ -97,6 +97,7 @@ extern int libevent_tests_running_in_debug_mode;
 #define TT_ENABLE_IOCP_FLAG	(TT_FIRST_USER_FLAG<<6)
 #define TT_ENABLE_IOCP		(TT_ENABLE_IOCP_FLAG|TT_NEED_THREADS)
 #define TT_ENABLE_DEBUG_MODE	(TT_ENABLE_IOCP_FLAG<<7)
+#define TT_ENABLE_PRIORITY_INHERITANCE	(TT_ENABLE_IOCP_FLAG<<8)
 
 /* All the flags that a legacy test needs. */
 #define TT_ISOLATED TT_FORK|TT_NEED_SOCKETPAIR|TT_NEED_BASE
diff --git a/test/regress_main.c b/test/regress_main.c
@@ -193,6 +193,12 @@ basic_test_setup(const struct testcase_t *testcase)
 	evutil_socket_t spair[2] = { -1, -1 };
 	struct basic_test_data *data = NULL;
 
+#if defined(EVTHREAD_USE_PTHREADS_IMPLEMENTED)
+	int evthread_flags = 0;
+	if (testcase->flags & TT_ENABLE_PRIORITY_INHERITANCE)
+		evthread_flags |= EVTHREAD_PTHREAD_PRIO_INHERIT;
+#endif
+
 #ifndef _WIN32
 	if (testcase->flags & TT_ENABLE_IOCP_FLAG)
 		return (void*)TT_SKIP;
@@ -208,7 +214,7 @@ basic_test_setup(const struct testcase_t *testcase)
 		if (!(testcase->flags & TT_FORK))
 			return NULL;
 #if defined(EVTHREAD_USE_PTHREADS_IMPLEMENTED)
-		if (evthread_use_pthreads())
+		if (evthread_use_pthreads_with_flags(evthread_flags))
 			exit(1);
 #elif defined(EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED)
 		if (evthread_use_windows_threads())
diff --git a/test/regress_thread.c b/test/regress_thread.c
@@ -574,6 +574,9 @@ struct testcase_t thread_testcases[] = {
 #ifndef _WIN32
 	{ "forking", thread_basic, TT_FORK|TT_NEED_THREADS|TT_NEED_BASE,
 	  &basic_setup, (char*)"forking" },
+	{ "priority_inheritance", thread_basic,
+	  TT_FORK|TT_NEED_THREADS|TT_NEED_BASE|TT_ENABLE_PRIORITY_INHERITANCE,
+	  &basic_setup, (char*)"priority_inheritance" },
 #endif
 	TEST(conditions_simple, TT_RETRIABLE),
 	{ "deferred_cb_skew", thread_deferred_cb_skew,
