[vlc-devel] [PATCH 2/3] win32: implement non-recursive locks

[Steve Lhomme]

For non-recursive locks we keep track of the thread having the lock and make
sure it's not the current thread that already had the lock.

lock_thread_id & b_recursive are always accessed in the CriticalSection
---
 include/vlc_threads.h |  9 ++++++++-
 src/win32/thread.c    | 18 +++++++++++++++---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/vlc_threads.h b/include/vlc_threads.h
index 33b9b53..becd9d6 100644
--- a/include/vlc_threads.h
+++ b/include/vlc_threads.h
@@ -65,7 +65,14 @@ typedef struct
             bool locked;
             unsigned long contention;
         };
-        CRITICAL_SECTION mutex;
+        struct
+        {
+            CRITICAL_SECTION mutex;
+
+            /* non-recursive mutex */
+            bool b_recursive;
+            unsigned long lock_thread_id;
+        };
     };
 } vlc_mutex_t;
 #define VLC_STATIC_MUTEX { false, { { false, 0 } } }
diff --git a/src/win32/thread.c b/src/win32/thread.c
index 963a8d7..de611e8 100644
--- a/src/win32/thread.c
+++ b/src/win32/thread.c
@@ -69,16 +69,16 @@ struct vlc_thread
 /*** Mutexes ***/
 void vlc_mutex_init( vlc_mutex_t *p_mutex )
 {
-    /* This creates a recursive mutex. This is OK as fast mutexes have
-     * no defined behavior in case of recursive locking. */
     InitializeCriticalSection (&p_mutex->mutex);
     p_mutex->dynamic = true;
+    p_mutex->b_recursive = false;
 }
 
 void vlc_mutex_init_recursive( vlc_mutex_t *p_mutex )
 {
     InitializeCriticalSection( &p_mutex->mutex );
     p_mutex->dynamic = true;
+    p_mutex->b_recursive = true;
 }
 
 
@@ -109,6 +109,8 @@ void vlc_mutex_lock (vlc_mutex_t *p_mutex)
     }
 
     EnterCriticalSection (&p_mutex->mutex);
+    assert(p_mutex->b_recursive || p_mutex->lock_thread_id != vlc_thread_id());
+    p_mutex->lock_thread_id = vlc_thread_id();
 }
 
 int vlc_mutex_trylock (vlc_mutex_t *p_mutex)
@@ -128,7 +130,16 @@ int vlc_mutex_trylock (vlc_mutex_t *p_mutex)
         return ret;
     }
 
-    return TryEnterCriticalSection (&p_mutex->mutex) ? 0 : EBUSY;
+    int ret = TryEnterCriticalSection (&p_mutex->mutex);
+    assert(p_mutex->b_recursive || p_mutex->lock_thread_id != vlc_thread_id());
+    if (!ret)
+        return EBUSY;
+
+    if (!p_mutex->b_recursive && p_mutex->lock_thread_id == vlc_thread_id())
+        return EBUSY; /* we already had the non-recursive lock */
+
+    p_mutex->lock_thread_id = vlc_thread_id();
+    return 0;
 }
 
 void vlc_mutex_unlock (vlc_mutex_t *p_mutex)
@@ -146,6 +157,7 @@ void vlc_mutex_unlock (vlc_mutex_t *p_mutex)
         return;
     }
 
+    p_mutex->lock_thread_id = 0;
     LeaveCriticalSection (&p_mutex->mutex);
 }
 
-- 
2.7.0