Ticket #5693: spin-lock.patch

src/system/libroot/posix/pthread/Jamfile

@@ -18 +18 @@
     pthread_mutexattr.c
     pthread_once.cpp
     pthread_rwlock.cpp
+    pthread_spinlock.c
 ;
 

src/system/libroot/posix/pthread/pthread_spinlock.c

@@ +1 @@
+/*
+ * Copyright 2010, Lucian Adrian Grijincu, lucian.grijincu@gmail.com.
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <pthread.h>
+#include "pthread_private.h"
+
+
+
+#define SUNLOCKED   0
+#define SLOCKED     1
+
+
+
+int
+pthread_spin_init(pthread_spinlock_t* slock, int pshared)
+{
+    // this implementation of spinlocks doesn't differentiate
+    // between spin locks used by threads in the same process or
+    // between of different processes.
+
+    slock->lock = SUNLOCKED;
+    return 0;
+}
+
+
+int
+pthread_spin_destroy(pthread_spinlock_t* slock)
+{
+    return 0;
+}
+
+
+int
+pthread_spin_lock(pthread_spinlock_t* slock)
+{
+    // test and test-and-set semantics:
+    //  loop with low overhead reads until the spinlock seems unlocked
+    //  and then use the high-overhead test-and-set operation to try to
+    //  acquire the spinlock
+
+    while (slock->lock == SLOCKED
+            || atomic_test_and_set(&slock->lock, SLOCKED, SUNLOCKED) == SLOCKED)
+        ; // spin
+    return 0;
+}
+
+
+int
+pthread_spin_trylock(pthread_spinlock_t* slock)
+{
+    // implemented with test and test-and-set semantics
+    // as in pthread_spin_lock
+
+    if (slock->lock == SLOCKED)
+        return EBUSY;
+    if (atomic_test_and_set(&slock->lock, SLOCKED, SUNLOCKED) == SLOCKED)
+        return EBUSY;
+    return 0;
+}
+
+
+int
+pthread_spin_unlock(pthread_spinlock_t* slock)
+{
+    slock->lock = SUNLOCKED;
+    return 0;
+}
+

headers/posix/pthread.h

@@ -21 +21 @@
 typedef struct  _pthread_once       pthread_once_t;
 typedef struct  _pthread_rwlock     pthread_rwlock_t;
 typedef struct  _pthread_rwlockattr *pthread_rwlockattr_t;
+typedef struct  _pthread_spinlock   pthread_spinlock_t;
 /*
 typedef struct  _pthread_barrier    *pthread_barrier_t;
 typedef struct  _pthread_barrierattr *pthread_barrierattr_t;
-typedef struct  _pthread_spinlock   *pthread_spinlock_t;
 */
 
 struct _pthread_mutex {
@@ -64 +64 @@
     };
 };
 
+struct _pthread_spinlock {
+    int32_t     lock;
+};
+
 #define PTHREAD_MUTEX_DEFAULT       0
 #define PTHREAD_MUTEX_NORMAL        1
 #define PTHREAD_MUTEX_ERRORCHECK    2
@@ -206 +210 @@
 extern int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr,
     int shared);
 
+/* spinlock functions */
+extern int pthread_spin_init(pthread_spinlock_t* spinlock, int pshared);
+extern int pthread_spin_destroy(pthread_spinlock_t* spinlock);
+extern int pthread_spin_lock(pthread_spinlock_t* spinlock);
+extern int pthread_spin_trylock(pthread_spinlock_t* spinlock);
+extern int pthread_spin_unlock(pthread_spinlock_t* spinlock);
+
 /* misc. functions */
 extern int pthread_atfork(void (*prepare)(void), void (*parent)(void),
     void (*child)(void));