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pg_include/storage/pg_sema.h

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+/*-------------------------------------------------------------------------
+ *
+ * pg_sema.h
+ *	  Platform-independent API for semaphores.
+ *
+ * PostgreSQL requires counting semaphores (the kind that keep track of
+ * multiple unlock operations, and will allow an equal number of subsequent
+ * lock operations before blocking).  The underlying implementation is
+ * not the same on every platform.	This file defines the API that must
+ * be provided by each port.
+ *
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/pg_sema.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_SEMA_H
+#define PG_SEMA_H
+
+/*
+ * PGSemaphoreData and pointer type PGSemaphore are the data structure
+ * representing an individual semaphore.  The contents of PGSemaphoreData
+ * vary across implementations and must never be touched by platform-
+ * independent code.  PGSemaphoreData structures are always allocated
+ * in shared memory (to support implementations where the data changes during
+ * lock/unlock).
+ *
+ * pg_config.h must define exactly one of the USE_xxx_SEMAPHORES symbols.
+ */
+
+#ifdef USE_NAMED_POSIX_SEMAPHORES
+
+#include <semaphore.h>
+
+typedef sem_t *PGSemaphoreData;
+#endif
+
+#ifdef USE_UNNAMED_POSIX_SEMAPHORES
+
+#include <semaphore.h>
+
+typedef sem_t PGSemaphoreData;
+#endif
+
+#ifdef USE_SYSV_SEMAPHORES
+
+typedef struct PGSemaphoreData
+{
+	int			semId;			/* semaphore set identifier */
+	int			semNum;			/* semaphore number within set */
+} PGSemaphoreData;
+#endif
+
+#ifdef USE_WIN32_SEMAPHORES
+
+typedef HANDLE PGSemaphoreData;
+#endif
+
+typedef PGSemaphoreData *PGSemaphore;
+
+
+/* Module initialization (called during postmaster start or shmem reinit) */
+extern void PGReserveSemaphores(int maxSemas, int port);
+
+/* Initialize a PGSemaphore structure to represent a sema with count 1 */
+extern void PGSemaphoreCreate(PGSemaphore sema);
+
+/* Reset a previously-initialized PGSemaphore to have count 0 */
+extern void PGSemaphoreReset(PGSemaphore sema);
+
+/* Lock a semaphore (decrement count), blocking if count would be < 0 */
+extern void PGSemaphoreLock(PGSemaphore sema, bool interruptOK);
+
+/* Unlock a semaphore (increment count) */
+extern void PGSemaphoreUnlock(PGSemaphore sema);
+
+/* Lock a semaphore only if able to do so without blocking */
+extern bool PGSemaphoreTryLock(PGSemaphore sema);
+
+#endif   /* PG_SEMA_H */