initial import

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

barrier.h

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+/*
+ * barrier.h
+ *
+ * This header file describes the "barrier" synchronization
+ * construct. The type barrier_t describes the full state of the
+ * barrier including the POSIX 1003.1c synchronization objects
+ * necessary.
+ *
+ * A barrier causes threads to wait until a set of threads has
+ * all "reached" the barrier. The number of threads required is
+ * set when the barrier is initialized, and cannot be changed
+ * except by reinitializing.
+ */
+#include <pthread.h>
+
+/*
+ * Structure describing a barrier.
+ */
+typedef struct barrier_tag {
+    pthread_mutex_t     mutex;          /* Control access to barrier */
+    pthread_cond_t      cv;             /* wait for barrier */
+    int                 valid;          /* set when valid */
+    int                 threshold;      /* number of threads required */
+    int                 counter;        /* current number of threads */
+    int                 cycle;          /* alternate wait cycles (0 or 1) */
+} barrier_t;
+
+#define BARRIER_VALID   0xdbcafe
+
+/*
+ * Support static initialization of barriers
+ */
+#define BARRIER_INITIALIZER(cnt) \
+    {PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, \
+    BARRIER_VALID, cnt, cnt, 0}
+
+/*
+ * Define barrier functions
+ */
+extern int barrier_init (barrier_t *barrier, int count);
+extern int barrier_destroy (barrier_t *barrier);
+extern int barrier_wait (barrier_t *barrier);