initial import

from
http://www.informit.com/store/programming-with-posix-threads-9780201633924

rwlock.h

@@ -0,0 +1,49 @@
+/*
+ * rwlock.h
+ *
+ * This header file describes the "reader/writer lock" synchronization
+ * construct. The type rwlock_t describes the full state of the lock
+ * including the POSIX 1003.1c synchronization objects necessary.
+ *
+ * A reader/writer lock allows a thread to lock shared data either for shared
+ * read access or exclusive write access.
+ *
+ * The rwl_init() and rwl_destroy() functions, respectively, allow you to
+ * initialize/create and destroy/free the reader/writer lock.
+ */
+#include <pthread.h>
+
+/*
+ * Structure describing a read-write lock.
+ */
+typedef struct rwlock_tag {
+    pthread_mutex_t     mutex;
+    pthread_cond_t      read;           /* wait for read */
+    pthread_cond_t      write;          /* wait for write */
+    int                 valid;          /* set when valid */
+    int                 r_active;       /* readers active */
+    int                 w_active;       /* writer active */
+    int                 r_wait;         /* readers waiting */
+    int                 w_wait;         /* writers waiting */
+} rwlock_t;
+
+#define RWLOCK_VALID    0xfacade
+
+/*
+ * Support static initialization of barriers
+ */
+#define RWL_INITIALIZER \
+    {PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, \
+    PTHREAD_COND_INITIALIZER, RWLOCK_VALID, 0, 0, 0, 0}
+
+/*
+ * Define read-write lock functions
+ */
+extern int rwl_init (rwlock_t *rwlock);
+extern int rwl_destroy (rwlock_t *rwlock);
+extern int rwl_readlock (rwlock_t *rwlock);
+extern int rwl_readtrylock (rwlock_t *rwlock);
+extern int rwl_readunlock (rwlock_t *rwlock);
+extern int rwl_writelock (rwlock_t *rwlock);
+extern int rwl_writetrylock (rwlock_t *rwlock);
+extern int rwl_writeunlock (rwlock_t *rwlock);