unix,win: add uv_mutex_init_recursive()

Support the creation of recursive mutexes on Unix. A matching
API is added on Windows, however mutexes on Windows are always
recursive.

Refs: https://github.com/libuv/libuv/issues/1022
PR-URL: https://github.com/libuv/libuv/pull/1555
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

docs/src/guide/threads.rst

@@ -79,18 +79,21 @@ The mutex functions are a **direct** map to the pthread equivalents.
 .. literalinclude:: ../../../include/uv.h
     :lines: 1355-1360
 
-The ``uv_mutex_init()`` and ``uv_mutex_trylock()`` functions will return 0 on
-success, and an error code otherwise.
+The ``uv_mutex_init()``, ``uv_mutex_init_recursive()`` and ``uv_mutex_trylock()``
+functions will return 0 on success, and an error code otherwise.
 
 If `libuv` has been compiled with debugging enabled, ``uv_mutex_destroy()``,
 ``uv_mutex_lock()`` and ``uv_mutex_unlock()`` will ``abort()`` on error.
 Similarly ``uv_mutex_trylock()`` will abort if the error is anything *other
 than* ``EAGAIN`` or ``EBUSY``.
 
-Recursive mutexes are supported by some platforms, but you should not rely on
-them. The BSD mutex implementation will raise an error if a thread which has
+Recursive mutexes are supported, but you should not rely on them. Also, they
+should not be used with ``uv_cond_t`` variables.
+
+The default BSD mutex implementation will raise an error if a thread which has
 locked a mutex attempts to lock it again. For example, a construct like::
 
+    uv_mutex_init(a_mutex);
     uv_mutex_lock(a_mutex);
     uv_thread_create(thread_id, entry, (void *)a_mutex);
     uv_mutex_lock(a_mutex);
@@ -102,8 +105,7 @@ return an error in the second call to ``uv_mutex_lock()``.
 
 .. note::
 
-    Mutexes on linux support attributes for a recursive mutex, but the API is
-    not exposed via libuv.
+    Mutexes on Windows are always recursive.
 
 Locks
 ~~~~~

docs/src/threading.rst

@@ -91,6 +91,7 @@ Functions return 0 on success or an error code < 0 (unless the
 return type is void, of course).
 
 .. c:function:: int uv_mutex_init(uv_mutex_t* handle)
+.. c:function:: int uv_mutex_init_recursive(uv_mutex_t* handle)
 .. c:function:: void uv_mutex_destroy(uv_mutex_t* handle)
 .. c:function:: void uv_mutex_lock(uv_mutex_t* handle)
 .. c:function:: int uv_mutex_trylock(uv_mutex_t* handle)

include/uv.h

@@ -1424,6 +1424,7 @@ UV_EXTERN int uv_dlsym(uv_lib_t* lib, const char* name, void** ptr);
 UV_EXTERN const char* uv_dlerror(const uv_lib_t* lib);
 
 UV_EXTERN int uv_mutex_init(uv_mutex_t* handle);
+UV_EXTERN int uv_mutex_init_recursive(uv_mutex_t* handle);
 UV_EXTERN void uv_mutex_destroy(uv_mutex_t* handle);
 UV_EXTERN void uv_mutex_lock(uv_mutex_t* handle);
 UV_EXTERN int uv_mutex_trylock(uv_mutex_t* handle);

src/unix/thread.c

@@ -241,6 +241,25 @@ int uv_mutex_init(uv_mutex_t* mutex) {
 }
 
 
+int uv_mutex_init_recursive(uv_mutex_t* mutex) {
+  pthread_mutexattr_t attr;
+  int err;
+
+  if (pthread_mutexattr_init(&attr))
+    abort();
+
+  if (pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE))
+    abort();
+
+  err = pthread_mutex_init(mutex, &attr);
+
+  if (pthread_mutexattr_destroy(&attr))
+    abort();
+
+  return -err;
+}
+
+
 void uv_mutex_destroy(uv_mutex_t* mutex) {
   if (pthread_mutex_destroy(mutex))
     abort();

src/win/thread.c

@@ -198,6 +198,11 @@ int uv_mutex_init(uv_mutex_t* mutex) {
 }
 
 
+int uv_mutex_init_recursive(uv_mutex_t* mutex) {
+  return uv_mutex_init(mutex);
+}
+
+
 void uv_mutex_destroy(uv_mutex_t* mutex) {
   DeleteCriticalSection(mutex);
 }

test/test-list.h

@@ -328,6 +328,7 @@ TEST_DECLARE   (threadpool_cancel_single)
 TEST_DECLARE   (thread_local_storage)
 TEST_DECLARE   (thread_stack_size)
 TEST_DECLARE   (thread_mutex)
+TEST_DECLARE   (thread_mutex_recursive)
 TEST_DECLARE   (thread_rwlock)
 TEST_DECLARE   (thread_rwlock_trylock)
 TEST_DECLARE   (thread_create)
@@ -840,6 +841,7 @@ TASK_LIST_START
   TEST_ENTRY  (thread_local_storage)
   TEST_ENTRY  (thread_stack_size)
   TEST_ENTRY  (thread_mutex)
+  TEST_ENTRY  (thread_mutex_recursive)
   TEST_ENTRY  (thread_rwlock)
   TEST_ENTRY  (thread_rwlock_trylock)
   TEST_ENTRY  (thread_create)

test/test-mutexes.c

@@ -50,6 +50,26 @@ TEST_IMPL(thread_mutex) {
 }
 
 
+TEST_IMPL(thread_mutex_recursive) {
+  uv_mutex_t mutex;
+  int r;
+
+  r = uv_mutex_init_recursive(&mutex);
+  ASSERT(r == 0);
+
+  uv_mutex_lock(&mutex);
+  uv_mutex_lock(&mutex);
+  ASSERT(0 == uv_mutex_trylock(&mutex));
+
+  uv_mutex_unlock(&mutex);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_unlock(&mutex);
+  uv_mutex_destroy(&mutex);
+
+  return 0;
+}
+
+
 TEST_IMPL(thread_rwlock) {
   uv_rwlock_t rwlock;
   int r;