mirror of https://github.com/postgres/postgres
semaphores. Qingqing ZhouREL8_2_STABLE
Bruce Momjian
20 years ago
parent
291724dfa8
commit
908f317b73
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/*-------------------------------------------------------------------------
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* |
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* win32_sema.c |
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* Microsoft Windows Win32 Semaphores Emulation |
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* |
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group |
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* |
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* IDENTIFICATION |
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* $Header: /cvsroot/pgsql/src/backend/port/win32_sema.c,v 1.1 2006/04/29 16:34:41 momjian Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "miscadmin.h" |
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#include "storage/ipc.h" |
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#include "storage/pg_sema.h" |
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static HANDLE *mySemSet; /* IDs of sema sets acquired so far */ |
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static int numSems; /* number of sema sets acquired so far */ |
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static int maxSems; /* allocated size of mySemaSet array */ |
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static void ReleaseSemaphores(int code, Datum arg); |
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/*
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* PGReserveSemaphores --- initialize semaphore support |
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* |
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* In the Win32 implementation, we acquire semaphores on-demand; the |
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* maxSemas parameter is just used to size the array that keeps track of |
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* acquired semas for subsequent releasing. We use anonymous semaphores |
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* so the semaphores are automatically freed when the last referencing |
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* process exits. |
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*/ |
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void PGReserveSemaphores(int maxSemas, int port) |
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{ |
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mySemSet = (HANDLE *)malloc(maxSemas * sizeof(HANDLE)); |
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if (mySemSet == NULL) |
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elog(PANIC, "out of memory"); |
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numSems = 0; |
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maxSems = maxSemas; |
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on_shmem_exit(ReleaseSemaphores, 0); |
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} |
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/*
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* Release semaphores at shutdown or shmem reinitialization |
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* |
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* (called as an on_shmem_exit callback, hence funny argument list) |
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*/ |
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static void |
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ReleaseSemaphores(int code, Datum arg) |
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{ |
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int i; |
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for (i = 0; i < numSems; i++) |
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CloseHandle(mySemSet[i]); |
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free(mySemSet); |
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} |
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/*
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* PGSemaphoreCreate |
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* |
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* Initialize a PGSemaphore structure to represent a sema with count 1 |
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*/ |
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void PGSemaphoreCreate(PGSemaphore sema) |
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{ |
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HANDLE cur_handle; |
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SECURITY_ATTRIBUTES sec_attrs; |
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/* Can't do this in a backend, because static state is postmaster's */ |
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Assert(!IsUnderPostmaster); |
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if (numSems >= maxSems) |
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elog(PANIC, "too many semaphores created"); |
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ZeroMemory(&sec_attrs, sizeof(sec_attrs)); |
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sec_attrs.nLength = sizeof(sec_attrs); |
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sec_attrs.lpSecurityDescriptor = NULL; |
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sec_attrs.bInheritHandle = TRUE; |
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/* We don't need a named semaphore */ |
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cur_handle = CreateSemaphore(&sec_attrs, 1, 1, NULL); |
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if (cur_handle) |
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{ |
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/* Successfully done */ |
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*sema = cur_handle; |
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mySemSet[numSems++] = cur_handle; |
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} |
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else |
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ereport(PANIC, |
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(errmsg("could not create semaphore: error code %d", (int)GetLastError()))); |
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} |
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/*
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* PGSemaphoreReset |
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* |
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* Reset a previously-initialized PGSemaphore to have count 0 |
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*/ |
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void PGSemaphoreReset(PGSemaphore sema) |
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{ |
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/*
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* There's no direct API for this in Win32, so we have to ratchet the |
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* semaphore down to 0 with repeated trylock's. |
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*/ |
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while (PGSemaphoreTryLock(sema)); |
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} |
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/*
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* PGSemaphoreLock |
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* |
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* Lock a semaphore (decrement count), blocking if count would be < 0. |
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* Serve the interrupt if interruptOK is true. |
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*/ |
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void PGSemaphoreLock(PGSemaphore sema, bool interruptOK) |
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{ |
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DWORD ret; |
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HANDLE wh[2]; |
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wh[0] = *sema; |
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wh[1] = pgwin32_signal_event; |
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do |
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{ |
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ImmediateInterruptOK = interruptOK; |
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CHECK_FOR_INTERRUPTS(); |
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errno = 0; |
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ret = WaitForMultipleObjectsEx(2, wh, FALSE, INFINITE, TRUE); |
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if (ret == WAIT_OBJECT_0) |
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{ |
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/* We got it! */ |
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return; |
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} |
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else if (ret == WAIT_OBJECT_0 + 1) |
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{ |
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/* Signal event is set - we have a signal to deliver */ |
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pgwin32_dispatch_queued_signals(); |
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errno = EINTR; |
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} |
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else |
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/* Otherwise we are in trouble */ |
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errno = EIDRM; |
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ImmediateInterruptOK = false; |
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} while (errno == EINTR); |
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if (errno != 0) |
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ereport(FATAL, |
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(errmsg("could not lock semaphore: error code %d", (int) GetLastError()))); |
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} |
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/*
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* PGSemaphoreUnlock |
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* |
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* Unlock a semaphore (increment count) |
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*/ |
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void PGSemaphoreUnlock(PGSemaphore sema) |
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{ |
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if (!ReleaseSemaphore(*sema, 1, NULL)) |
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ereport(FATAL, |
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(errmsg("could not unlock semaphore: error code %d", (int) GetLastError()))); |
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} |
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/*
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* PGSemaphoreTryLock |
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* |
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* Lock a semaphore only if able to do so without blocking |
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*/ |
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bool PGSemaphoreTryLock(PGSemaphore sema) |
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{ |
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DWORD ret; |
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ret = WaitForSingleObject(*sema, 0); |
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if (ret == WAIT_OBJECT_0) |
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{ |
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/* We got it! */ |
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return true; |
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} |
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else if (ret == WAIT_TIMEOUT) |
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{ |
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/* Can't get it */ |
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errno = EAGAIN; |
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return false; |
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} |
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/* Otherwise we are in trouble */ |
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ereport(FATAL, |
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(errmsg("could not try-lock semaphore: error code %d", (int) GetLastError()))); |
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/* keep compiler quiet */ |
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return false; |
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} |
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