diff options
Diffstat (limited to 'lib/windows-rwlock.c')
| -rw-r--r-- | lib/windows-rwlock.c | 377 |
1 files changed, 377 insertions, 0 deletions
diff --git a/lib/windows-rwlock.c b/lib/windows-rwlock.c new file mode 100644 index 0000000..d186e03 --- /dev/null +++ b/lib/windows-rwlock.c @@ -0,0 +1,377 @@ +/* Read-write locks (native Windows implementation). + Copyright (C) 2005-2022 Free Software Foundation, Inc. + + This file is free software: you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + This file is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* Written by Bruno Haible <bruno@clisp.org>, 2005. + Based on GCC's gthr-win32.h. */ + +#include <config.h> + +/* Specification. */ +#include "windows-rwlock.h" + +#include <errno.h> +#include <stdlib.h> + +/* Don't assume that UNICODE is not defined. */ +#undef CreateEvent +#define CreateEvent CreateEventA + +/* In this file, the waitqueues are implemented as circular arrays. */ +#define glwthread_waitqueue_t glwthread_carray_waitqueue_t + +static void +glwthread_waitqueue_init (glwthread_waitqueue_t *wq) +{ + wq->array = NULL; + wq->count = 0; + wq->alloc = 0; + wq->offset = 0; +} + +/* Enqueues the current thread, represented by an event, in a wait queue. + Returns INVALID_HANDLE_VALUE if an allocation failure occurs. */ +static HANDLE +glwthread_waitqueue_add (glwthread_waitqueue_t *wq) +{ + HANDLE event; + unsigned int index; + + if (wq->count == wq->alloc) + { + unsigned int new_alloc = 2 * wq->alloc + 1; + HANDLE *new_array = + (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE)); + if (new_array == NULL) + /* No more memory. */ + return INVALID_HANDLE_VALUE; + /* Now is a good opportunity to rotate the array so that its contents + starts at offset 0. */ + if (wq->offset > 0) + { + unsigned int old_count = wq->count; + unsigned int old_alloc = wq->alloc; + unsigned int old_offset = wq->offset; + unsigned int i; + if (old_offset + old_count > old_alloc) + { + unsigned int limit = old_offset + old_count - old_alloc; + for (i = 0; i < limit; i++) + new_array[old_alloc + i] = new_array[i]; + } + for (i = 0; i < old_count; i++) + new_array[i] = new_array[old_offset + i]; + wq->offset = 0; + } + wq->array = new_array; + wq->alloc = new_alloc; + } + /* Whether the created event is a manual-reset one or an auto-reset one, + does not matter, since we will wait on it only once. */ + event = CreateEvent (NULL, TRUE, FALSE, NULL); + if (event == INVALID_HANDLE_VALUE) + /* No way to allocate an event. */ + return INVALID_HANDLE_VALUE; + index = wq->offset + wq->count; + if (index >= wq->alloc) + index -= wq->alloc; + wq->array[index] = event; + wq->count++; + return event; +} + +/* Notifies the first thread from a wait queue and dequeues it. */ +static void +glwthread_waitqueue_notify_first (glwthread_waitqueue_t *wq) +{ + SetEvent (wq->array[wq->offset + 0]); + wq->offset++; + wq->count--; + if (wq->count == 0 || wq->offset == wq->alloc) + wq->offset = 0; +} + +/* Notifies all threads from a wait queue and dequeues them all. */ +static void +glwthread_waitqueue_notify_all (glwthread_waitqueue_t *wq) +{ + unsigned int i; + + for (i = 0; i < wq->count; i++) + { + unsigned int index = wq->offset + i; + if (index >= wq->alloc) + index -= wq->alloc; + SetEvent (wq->array[index]); + } + wq->count = 0; + wq->offset = 0; +} + +void +glwthread_rwlock_init (glwthread_rwlock_t *lock) +{ + InitializeCriticalSection (&lock->lock); + glwthread_waitqueue_init (&lock->waiting_readers); + glwthread_waitqueue_init (&lock->waiting_writers); + lock->runcount = 0; + lock->guard.done = 1; +} + +int +glwthread_rwlock_rdlock (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + { + if (InterlockedIncrement (&lock->guard.started) == 0) + /* This thread is the first one to need this lock. Initialize it. */ + glwthread_rwlock_init (lock); + else + { + /* Don't let lock->guard.started grow and wrap around. */ + InterlockedDecrement (&lock->guard.started); + /* Yield the CPU while waiting for another thread to finish + initializing this lock. */ + while (!lock->guard.done) + Sleep (0); + } + } + EnterCriticalSection (&lock->lock); + /* Test whether only readers are currently running, and whether the runcount + field will not overflow, and whether no writer is waiting. The latter + condition is because POSIX recommends that "write locks shall take + precedence over read locks", to avoid "writer starvation". */ + if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) + { + /* This thread has to wait for a while. Enqueue it among the + waiting_readers. */ + HANDLE event = glwthread_waitqueue_add (&lock->waiting_readers); + if (event != INVALID_HANDLE_VALUE) + { + DWORD result; + LeaveCriticalSection (&lock->lock); + /* Wait until another thread signals this event. */ + result = WaitForSingleObject (event, INFINITE); + if (result == WAIT_FAILED || result == WAIT_TIMEOUT) + abort (); + CloseHandle (event); + /* The thread which signalled the event already did the bookkeeping: + removed us from the waiting_readers, incremented lock->runcount. */ + if (!(lock->runcount > 0)) + abort (); + return 0; + } + else + { + /* Allocation failure. Weird. */ + do + { + LeaveCriticalSection (&lock->lock); + Sleep (1); + EnterCriticalSection (&lock->lock); + } + while (!(lock->runcount + 1 > 0)); + } + } + lock->runcount++; + LeaveCriticalSection (&lock->lock); + return 0; +} + +int +glwthread_rwlock_wrlock (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + { + if (InterlockedIncrement (&lock->guard.started) == 0) + /* This thread is the first one to need this lock. Initialize it. */ + glwthread_rwlock_init (lock); + else + { + /* Don't let lock->guard.started grow and wrap around. */ + InterlockedDecrement (&lock->guard.started); + /* Yield the CPU while waiting for another thread to finish + initializing this lock. */ + while (!lock->guard.done) + Sleep (0); + } + } + EnterCriticalSection (&lock->lock); + /* Test whether no readers or writers are currently running. */ + if (!(lock->runcount == 0)) + { + /* This thread has to wait for a while. Enqueue it among the + waiting_writers. */ + HANDLE event = glwthread_waitqueue_add (&lock->waiting_writers); + if (event != INVALID_HANDLE_VALUE) + { + DWORD result; + LeaveCriticalSection (&lock->lock); + /* Wait until another thread signals this event. */ + result = WaitForSingleObject (event, INFINITE); + if (result == WAIT_FAILED || result == WAIT_TIMEOUT) + abort (); + CloseHandle (event); + /* The thread which signalled the event already did the bookkeeping: + removed us from the waiting_writers, set lock->runcount = -1. */ + if (!(lock->runcount == -1)) + abort (); + return 0; + } + else + { + /* Allocation failure. Weird. */ + do + { + LeaveCriticalSection (&lock->lock); + Sleep (1); + EnterCriticalSection (&lock->lock); + } + while (!(lock->runcount == 0)); + } + } + lock->runcount--; /* runcount becomes -1 */ + LeaveCriticalSection (&lock->lock); + return 0; +} + +int +glwthread_rwlock_tryrdlock (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + { + if (InterlockedIncrement (&lock->guard.started) == 0) + /* This thread is the first one to need this lock. Initialize it. */ + glwthread_rwlock_init (lock); + else + { + /* Don't let lock->guard.started grow and wrap around. */ + InterlockedDecrement (&lock->guard.started); + /* Yield the CPU while waiting for another thread to finish + initializing this lock. */ + while (!lock->guard.done) + Sleep (0); + } + } + /* It's OK to wait for this critical section, because it is never taken for a + long time. */ + EnterCriticalSection (&lock->lock); + /* Test whether only readers are currently running, and whether the runcount + field will not overflow, and whether no writer is waiting. The latter + condition is because POSIX recommends that "write locks shall take + precedence over read locks", to avoid "writer starvation". */ + if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) + { + /* This thread would have to wait for a while. Return instead. */ + LeaveCriticalSection (&lock->lock); + return EBUSY; + } + lock->runcount++; + LeaveCriticalSection (&lock->lock); + return 0; +} + +int +glwthread_rwlock_trywrlock (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + { + if (InterlockedIncrement (&lock->guard.started) == 0) + /* This thread is the first one to need this lock. Initialize it. */ + glwthread_rwlock_init (lock); + else + { + /* Don't let lock->guard.started grow and wrap around. */ + InterlockedDecrement (&lock->guard.started); + /* Yield the CPU while waiting for another thread to finish + initializing this lock. */ + while (!lock->guard.done) + Sleep (0); + } + } + /* It's OK to wait for this critical section, because it is never taken for a + long time. */ + EnterCriticalSection (&lock->lock); + /* Test whether no readers or writers are currently running. */ + if (!(lock->runcount == 0)) + { + /* This thread would have to wait for a while. Return instead. */ + LeaveCriticalSection (&lock->lock); + return EBUSY; + } + lock->runcount--; /* runcount becomes -1 */ + LeaveCriticalSection (&lock->lock); + return 0; +} + +int +glwthread_rwlock_unlock (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + return EINVAL; + EnterCriticalSection (&lock->lock); + if (lock->runcount < 0) + { + /* Drop a writer lock. */ + if (!(lock->runcount == -1)) + abort (); + lock->runcount = 0; + } + else + { + /* Drop a reader lock. */ + if (!(lock->runcount > 0)) + { + LeaveCriticalSection (&lock->lock); + return EPERM; + } + lock->runcount--; + } + if (lock->runcount == 0) + { + /* POSIX recommends that "write locks shall take precedence over read + locks", to avoid "writer starvation". */ + if (lock->waiting_writers.count > 0) + { + /* Wake up one of the waiting writers. */ + lock->runcount--; + glwthread_waitqueue_notify_first (&lock->waiting_writers); + } + else + { + /* Wake up all waiting readers. */ + lock->runcount += lock->waiting_readers.count; + glwthread_waitqueue_notify_all (&lock->waiting_readers); + } + } + LeaveCriticalSection (&lock->lock); + return 0; +} + +int +glwthread_rwlock_destroy (glwthread_rwlock_t *lock) +{ + if (!lock->guard.done) + return EINVAL; + if (lock->runcount != 0) + return EBUSY; + DeleteCriticalSection (&lock->lock); + if (lock->waiting_readers.array != NULL) + free (lock->waiting_readers.array); + if (lock->waiting_writers.array != NULL) + free (lock->waiting_writers.array); + lock->guard.done = 0; + return 0; +} |