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db_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) 1996-2021, 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
+
+/*
+ * struct 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; hence, PGSemaphoreData is declared as an opaque struct here.
+ *
+ * However, Windows is sufficiently unlike our other ports that it doesn't
+ * seem worth insisting on ABI compatibility for Windows too.  Hence, on
+ * that platform just define PGSemaphore as HANDLE.
+ */
+#ifndef USE_WIN32_SEMAPHORES
+typedef struct PGSemaphoreData *PGSemaphore;
+#else
+typedef HANDLE PGSemaphore;
+#endif
+
+
+/* Report amount of shared memory needed */
+extern Size PGSemaphoreShmemSize(int maxSemas);
+
+/* Module initialization (called during postmaster start or shmem reinit) */
+extern void PGReserveSemaphores(int maxSemas);
+
+/* Allocate a PGSemaphore structure with initial count 1 */
+extern PGSemaphore PGSemaphoreCreate(void);
+
+/* 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);
+
+/* 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 */