Read/write locks

include/vlc_threads.h

@@ -107,6 +107,7 @@ typedef pthread_t       vlc_thread_t;
 typedef pthread_mutex_t vlc_mutex_t;
 #define VLC_STATIC_MUTEX PTHREAD_MUTEX_INITIALIZER
 typedef pthread_cond_t  vlc_cond_t;
+typedef pthread_rwlock_t vlc_rwlock_t;
 typedef pthread_key_t   vlc_threadvar_t;
 typedef struct vlc_timer_t vlc_timer_t;
 
@@ -143,6 +144,17 @@ typedef struct
 #define VLC_STATIC_MUTEX { 0, }
 
 typedef HANDLE  vlc_cond_t;
+
+typedef struct
+{
+    vlc_mutex_t   mutex;
+    vlc_cond_t    read_wait;
+    vlc_cond_t    write_wait;
+    unsigned long readers;
+    unsigned long writers;
+    DWORD         writer;
+} vlc_rwlock_t;
+
 typedef DWORD   vlc_threadvar_t;
 typedef struct vlc_timer_t vlc_timer_t;
 struct vlc_timer_t
@@ -176,6 +188,11 @@ VLC_EXPORT( void, vlc_cond_signal, (vlc_cond_t *) );
 VLC_EXPORT( void, vlc_cond_broadcast, (vlc_cond_t *) );
 VLC_EXPORT( void, vlc_cond_wait, (vlc_cond_t *, vlc_mutex_t *) );
 VLC_EXPORT( int, vlc_cond_timedwait, (vlc_cond_t *, vlc_mutex_t *, mtime_t) );
+VLC_EXPORT( void, vlc_rwlock_init, (vlc_rwlock_t *) );
+VLC_EXPORT( void, vlc_rwlock_destroy, (vlc_rwlock_t *) );
+VLC_EXPORT( void, vlc_rwlock_rdlock, (vlc_rwlock_t *) );
+VLC_EXPORT( void, vlc_rwlock_wrlock, (vlc_rwlock_t *) );
+VLC_EXPORT( void, vlc_rwlock_unlock, (vlc_rwlock_t *) );
 VLC_EXPORT( int, vlc_threadvar_create, (vlc_threadvar_t * , void (*) (void *) ) );
 VLC_EXPORT( void, vlc_threadvar_delete, (vlc_threadvar_t *) );
 VLC_EXPORT( int, vlc_threadvar_set, (vlc_threadvar_t, void *) );

src/libvlccore.sym

@@ -519,6 +519,11 @@ vlc_poll
 vlc_rand_bytes
 vlc_release
 vlc_restorecancel
+vlc_rwlock_destroy
+vlc_rwlock_init
+vlc_rwlock_rdlock
+vlc_rwlock_unlock
+vlc_rwlock_wrlock
 vlc_savecancel
 vlc_sd_Create
 vlc_sd_GetNames

src/misc/pthread.c

@@ -375,6 +375,51 @@ int vlc_cond_timedwait (vlc_cond_t *p_condvar, vlc_mutex_t *p_mutex,
     return val;
 }
 
+/**
+ * Initializes a read/write lock.
+ */
+void vlc_rwlock_init (vlc_rwlock_t *lock)
+{
+    if (pthread_rwlock_init (lock, NULL))
+        abort ();
+}
+
+/**
+ * Destroys an initialized unused read/write lock.
+ */
+void vlc_rwlock_destroy (vlc_rwlock_t *lock)
+{
+    int val = pthread_rwlock_destroy (lock);
+    VLC_THREAD_ASSERT ("destroying R/W lock");
+}
+
+/**
+ * Acquires a read/write lock for reading. Recursion is allowed.
+ */
+void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
+{
+    int val = pthread_rwlock_rdlock (lock);
+    VLC_THREAD_ASSERT ("acquiring R/W lock for reading");
+}
+
+/**
+ * Acquires a read/write lock for writing. Recursion is not allowed.
+ */
+void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
+{
+    int val = pthread_rwlock_wrlock (lock);
+    VLC_THREAD_ASSERT ("acquiring R/W lock for writing");
+}
+
+/**
+ * Releases a read/write lock.
+ */
+void vlc_rwlock_unlock (vlc_rwlock_t *lock)
+{
+    int val = pthread_rwlock_unlock (lock);
+    VLC_THREAD_ASSERT ("releasing R/W lock");
+}
+
 /**
  * Allocates a thread-specific variable.
  * @param key where to store the thread-specific variable handle

src/misc/w32thread.c

@@ -34,6 +34,7 @@
 #include "libvlc.h"
 #include <stdarg.h>
 #include <assert.h>
+#include <limits.h>
 
 static vlc_threadvar_t cancel_key;
 
@@ -291,6 +292,82 @@ int vlc_cond_timedwait (vlc_cond_t *p_condvar, vlc_mutex_t *p_mutex,
     return (result == WAIT_OBJECT_0) ? 0 : ETIMEDOUT;
 }
 
+/*** Read/write locks */
+/* SRW (Slim Read Write) locks are available in Vista+ only */
+void vlc_rwlock_init (vlc_rwlock_t *lock)
+{
+    vlc_mutex_init (&lock->mutex);
+    vlc_cond_init (&lock->read_wait);
+    vlc_cond_init (&lock->write_wait);
+    lock->readers = 0; /* active readers */
+    lock->writers = 0; /* waiting or active writers */
+    lock->writer = 0; /* ID of active writer */
+}
+
+/**
+ * Destroys an initialized unused read/write lock.
+ */
+void vlc_rwlock_destroy (vlc_rwlock_t *lock)
+{
+    vlc_cond_destroy (&lock->read_wait);
+    vlc_cond_destroy (&lock->write_wait);
+    vlc_mutex_destroy (&lock->mutex);
+}
+
+/**
+ * Acquires a read/write lock for reading. Recursion is allowed.
+ */
+void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
+{
+    vlc_mutex_lock (&lock->mutex);
+    while (lock->writers > 0) /* Favor writers to avoid starving */
+        vlc_cond_wait (&lock->read_wait, &lock->mutex);
+    if (lock->readers == ULONG_MAX)
+        abort ();
+    lock->readers++;
+    vlc_mutex_unlock (&lock->mutex);
+}
+
+/**
+ * Acquires a read/write lock for writing. Recursion is not allowed.
+ */
+void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
+{
+    vlc_mutex_lock (&lock->mutex);
+    if (lock->writers == ULONG_MAX)
+        abort ();
+    lock->writers++;
+    while ((lock->readers > 0) || (lock->writer != 0))
+        vlc_cond_wait (&lock->write_wait, &lock->mutex);
+    lock->writer = GetCurrentThreadId ();
+    vlc_mutex_unlock (&lock->mutex);
+}
+
+/**
+ * Releases a read/write lock.
+ */
+void vlc_rwlock_unlock (vlc_rwlock_t *lock)
+{
+    vlc_mutex_lock (&lock->mutex);
+    if (lock->readers > 0)
+        lock->readers--; /* Read unlock */
+    else
+    {
+        lock->writer = 0; /* Write unlock */
+        assert (lock->writers > 0);
+        lock->writers--;
+    }
+
+    if (lock->writers > 0)
+    {
+        if (lock->readers == 0)
+            vlc_cond_signal (&lock->write_wait);
+    }
+    else
+        vlc_cond_broadcast (&lock->read_wait);
+    vlc_mutex_unlock (&lock->mutex);
+}
+
 /*** Thread-specific variables (TLS) ***/
 int vlc_threadvar_create (vlc_threadvar_t *p_tls, void (*destr) (void *))
 {