378 lines
12 KiB
C
378 lines
12 KiB
C
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/* Read-write locks (native Windows implementation).
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Copyright (C) 2005-2021 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <https://www.gnu.org/licenses/>. */
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/* Written by Bruno Haible <bruno@clisp.org>, 2005.
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Based on GCC's gthr-win32.h. */
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#include <config.h>
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/* Specification. */
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#include "windows-rwlock.h"
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#include <errno.h>
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#include <stdlib.h>
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/* Don't assume that UNICODE is not defined. */
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#undef CreateEvent
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#define CreateEvent CreateEventA
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/* In this file, the waitqueues are implemented as circular arrays. */
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#define glwthread_waitqueue_t glwthread_carray_waitqueue_t
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static void
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glwthread_waitqueue_init (glwthread_waitqueue_t *wq)
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{
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wq->array = NULL;
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wq->count = 0;
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wq->alloc = 0;
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wq->offset = 0;
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}
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/* Enqueues the current thread, represented by an event, in a wait queue.
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Returns INVALID_HANDLE_VALUE if an allocation failure occurs. */
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static HANDLE
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glwthread_waitqueue_add (glwthread_waitqueue_t *wq)
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{
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HANDLE event;
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unsigned int index;
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if (wq->count == wq->alloc)
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{
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unsigned int new_alloc = 2 * wq->alloc + 1;
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HANDLE *new_array =
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(HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE));
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if (new_array == NULL)
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/* No more memory. */
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return INVALID_HANDLE_VALUE;
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/* Now is a good opportunity to rotate the array so that its contents
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starts at offset 0. */
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if (wq->offset > 0)
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{
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unsigned int old_count = wq->count;
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unsigned int old_alloc = wq->alloc;
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unsigned int old_offset = wq->offset;
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unsigned int i;
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if (old_offset + old_count > old_alloc)
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{
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unsigned int limit = old_offset + old_count - old_alloc;
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for (i = 0; i < limit; i++)
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new_array[old_alloc + i] = new_array[i];
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}
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for (i = 0; i < old_count; i++)
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new_array[i] = new_array[old_offset + i];
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wq->offset = 0;
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}
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wq->array = new_array;
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wq->alloc = new_alloc;
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}
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/* Whether the created event is a manual-reset one or an auto-reset one,
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does not matter, since we will wait on it only once. */
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event = CreateEvent (NULL, TRUE, FALSE, NULL);
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if (event == INVALID_HANDLE_VALUE)
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/* No way to allocate an event. */
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return INVALID_HANDLE_VALUE;
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index = wq->offset + wq->count;
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if (index >= wq->alloc)
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index -= wq->alloc;
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wq->array[index] = event;
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wq->count++;
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return event;
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}
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/* Notifies the first thread from a wait queue and dequeues it. */
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static void
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glwthread_waitqueue_notify_first (glwthread_waitqueue_t *wq)
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{
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SetEvent (wq->array[wq->offset + 0]);
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wq->offset++;
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wq->count--;
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if (wq->count == 0 || wq->offset == wq->alloc)
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wq->offset = 0;
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}
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/* Notifies all threads from a wait queue and dequeues them all. */
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static void
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glwthread_waitqueue_notify_all (glwthread_waitqueue_t *wq)
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{
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unsigned int i;
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for (i = 0; i < wq->count; i++)
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{
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unsigned int index = wq->offset + i;
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if (index >= wq->alloc)
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index -= wq->alloc;
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SetEvent (wq->array[index]);
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}
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wq->count = 0;
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wq->offset = 0;
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}
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void
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glwthread_rwlock_init (glwthread_rwlock_t *lock)
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{
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InitializeCriticalSection (&lock->lock);
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glwthread_waitqueue_init (&lock->waiting_readers);
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glwthread_waitqueue_init (&lock->waiting_writers);
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lock->runcount = 0;
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lock->guard.done = 1;
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}
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int
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glwthread_rwlock_rdlock (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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{
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if (InterlockedIncrement (&lock->guard.started) == 0)
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/* This thread is the first one to need this lock. Initialize it. */
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glwthread_rwlock_init (lock);
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else
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{
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/* Don't let lock->guard.started grow and wrap around. */
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InterlockedDecrement (&lock->guard.started);
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/* Yield the CPU while waiting for another thread to finish
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initializing this lock. */
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while (!lock->guard.done)
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Sleep (0);
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}
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}
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EnterCriticalSection (&lock->lock);
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/* Test whether only readers are currently running, and whether the runcount
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field will not overflow, and whether no writer is waiting. The latter
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condition is because POSIX recommends that "write locks shall take
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precedence over read locks", to avoid "writer starvation". */
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if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0))
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{
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/* This thread has to wait for a while. Enqueue it among the
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waiting_readers. */
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HANDLE event = glwthread_waitqueue_add (&lock->waiting_readers);
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if (event != INVALID_HANDLE_VALUE)
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{
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DWORD result;
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LeaveCriticalSection (&lock->lock);
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/* Wait until another thread signals this event. */
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result = WaitForSingleObject (event, INFINITE);
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if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
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abort ();
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CloseHandle (event);
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/* The thread which signalled the event already did the bookkeeping:
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removed us from the waiting_readers, incremented lock->runcount. */
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if (!(lock->runcount > 0))
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abort ();
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return 0;
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}
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else
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{
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/* Allocation failure. Weird. */
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do
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{
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LeaveCriticalSection (&lock->lock);
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Sleep (1);
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EnterCriticalSection (&lock->lock);
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}
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while (!(lock->runcount + 1 > 0));
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}
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}
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lock->runcount++;
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LeaveCriticalSection (&lock->lock);
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return 0;
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}
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int
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glwthread_rwlock_wrlock (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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{
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if (InterlockedIncrement (&lock->guard.started) == 0)
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/* This thread is the first one to need this lock. Initialize it. */
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glwthread_rwlock_init (lock);
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else
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{
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/* Don't let lock->guard.started grow and wrap around. */
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InterlockedDecrement (&lock->guard.started);
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/* Yield the CPU while waiting for another thread to finish
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initializing this lock. */
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while (!lock->guard.done)
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Sleep (0);
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}
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}
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EnterCriticalSection (&lock->lock);
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/* Test whether no readers or writers are currently running. */
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if (!(lock->runcount == 0))
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{
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/* This thread has to wait for a while. Enqueue it among the
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waiting_writers. */
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HANDLE event = glwthread_waitqueue_add (&lock->waiting_writers);
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if (event != INVALID_HANDLE_VALUE)
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{
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DWORD result;
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LeaveCriticalSection (&lock->lock);
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/* Wait until another thread signals this event. */
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result = WaitForSingleObject (event, INFINITE);
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if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
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abort ();
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CloseHandle (event);
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/* The thread which signalled the event already did the bookkeeping:
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removed us from the waiting_writers, set lock->runcount = -1. */
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if (!(lock->runcount == -1))
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abort ();
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return 0;
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}
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else
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{
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/* Allocation failure. Weird. */
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do
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{
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LeaveCriticalSection (&lock->lock);
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Sleep (1);
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EnterCriticalSection (&lock->lock);
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}
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while (!(lock->runcount == 0));
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}
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}
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lock->runcount--; /* runcount becomes -1 */
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LeaveCriticalSection (&lock->lock);
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return 0;
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}
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int
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glwthread_rwlock_tryrdlock (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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{
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if (InterlockedIncrement (&lock->guard.started) == 0)
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/* This thread is the first one to need this lock. Initialize it. */
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glwthread_rwlock_init (lock);
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else
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{
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/* Don't let lock->guard.started grow and wrap around. */
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InterlockedDecrement (&lock->guard.started);
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/* Yield the CPU while waiting for another thread to finish
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initializing this lock. */
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while (!lock->guard.done)
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Sleep (0);
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}
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}
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/* It's OK to wait for this critical section, because it is never taken for a
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long time. */
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EnterCriticalSection (&lock->lock);
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/* Test whether only readers are currently running, and whether the runcount
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field will not overflow, and whether no writer is waiting. The latter
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condition is because POSIX recommends that "write locks shall take
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precedence over read locks", to avoid "writer starvation". */
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if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0))
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{
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/* This thread would have to wait for a while. Return instead. */
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LeaveCriticalSection (&lock->lock);
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return EBUSY;
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}
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lock->runcount++;
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LeaveCriticalSection (&lock->lock);
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return 0;
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}
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int
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glwthread_rwlock_trywrlock (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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{
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if (InterlockedIncrement (&lock->guard.started) == 0)
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/* This thread is the first one to need this lock. Initialize it. */
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glwthread_rwlock_init (lock);
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else
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{
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/* Don't let lock->guard.started grow and wrap around. */
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InterlockedDecrement (&lock->guard.started);
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/* Yield the CPU while waiting for another thread to finish
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initializing this lock. */
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while (!lock->guard.done)
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Sleep (0);
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}
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}
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/* It's OK to wait for this critical section, because it is never taken for a
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long time. */
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EnterCriticalSection (&lock->lock);
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/* Test whether no readers or writers are currently running. */
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if (!(lock->runcount == 0))
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{
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/* This thread would have to wait for a while. Return instead. */
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LeaveCriticalSection (&lock->lock);
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return EBUSY;
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}
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lock->runcount--; /* runcount becomes -1 */
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LeaveCriticalSection (&lock->lock);
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return 0;
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}
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int
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glwthread_rwlock_unlock (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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return EINVAL;
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EnterCriticalSection (&lock->lock);
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if (lock->runcount < 0)
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{
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/* Drop a writer lock. */
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if (!(lock->runcount == -1))
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abort ();
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lock->runcount = 0;
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}
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else
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{
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/* Drop a reader lock. */
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if (!(lock->runcount > 0))
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{
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LeaveCriticalSection (&lock->lock);
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return EPERM;
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}
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lock->runcount--;
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}
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if (lock->runcount == 0)
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{
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/* POSIX recommends that "write locks shall take precedence over read
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locks", to avoid "writer starvation". */
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if (lock->waiting_writers.count > 0)
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{
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/* Wake up one of the waiting writers. */
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lock->runcount--;
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glwthread_waitqueue_notify_first (&lock->waiting_writers);
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}
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else
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{
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/* Wake up all waiting readers. */
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lock->runcount += lock->waiting_readers.count;
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glwthread_waitqueue_notify_all (&lock->waiting_readers);
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}
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}
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LeaveCriticalSection (&lock->lock);
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return 0;
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}
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int
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glwthread_rwlock_destroy (glwthread_rwlock_t *lock)
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{
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if (!lock->guard.done)
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return EINVAL;
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if (lock->runcount != 0)
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return EBUSY;
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DeleteCriticalSection (&lock->lock);
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if (lock->waiting_readers.array != NULL)
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free (lock->waiting_readers.array);
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if (lock->waiting_writers.array != NULL)
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free (lock->waiting_writers.array);
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lock->guard.done = 0;
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return 0;
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}
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