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2da61b671e
QemuMutex does not guarantee fairness and cannot be acquired recursively: Fairness means each locker gets a turn and the scheduler cannot cause starvation. Recursive locking is useful for composition, it allows a sequence of locking operations to be invoked atomically by acquiring the lock around them. This patch adds RFifoLock, a recursive lock that guarantees FIFO order. Its first user is added in the next patch. RFifoLock has one additional feature: it can be initialized with an optional contention callback. The callback is invoked whenever a thread must wait for the lock. For example, it can be used to poke the current owner so that they release the lock soon. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
92 lines
2.1 KiB
C
92 lines
2.1 KiB
C
/*
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* RFifoLock tests
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*
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* Copyright Red Hat, Inc. 2013
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*/
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#include <glib.h>
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#include "qemu-common.h"
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#include "qemu/rfifolock.h"
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static void test_nesting(void)
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{
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RFifoLock lock;
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/* Trivial test, ensure the lock is recursive */
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rfifolock_init(&lock, NULL, NULL);
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rfifolock_lock(&lock);
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rfifolock_lock(&lock);
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rfifolock_lock(&lock);
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rfifolock_unlock(&lock);
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rfifolock_unlock(&lock);
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rfifolock_unlock(&lock);
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rfifolock_destroy(&lock);
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}
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typedef struct {
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RFifoLock lock;
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int fd[2];
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} CallbackTestData;
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static void rfifolock_cb(void *opaque)
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{
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CallbackTestData *data = opaque;
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int ret;
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char c = 0;
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ret = write(data->fd[1], &c, sizeof(c));
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g_assert(ret == 1);
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}
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static void *callback_thread(void *opaque)
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{
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CallbackTestData *data = opaque;
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/* The other thread holds the lock so the contention callback will be
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* invoked...
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*/
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rfifolock_lock(&data->lock);
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rfifolock_unlock(&data->lock);
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return NULL;
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}
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static void test_callback(void)
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{
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CallbackTestData data;
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QemuThread thread;
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int ret;
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char c;
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rfifolock_init(&data.lock, rfifolock_cb, &data);
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ret = qemu_pipe(data.fd);
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g_assert(ret == 0);
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/* Hold lock but allow the callback to kick us by writing to the pipe */
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rfifolock_lock(&data.lock);
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qemu_thread_create(&thread, "callback_thread",
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callback_thread, &data, QEMU_THREAD_JOINABLE);
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ret = read(data.fd[0], &c, sizeof(c));
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g_assert(ret == 1);
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rfifolock_unlock(&data.lock);
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/* If we got here then the callback was invoked, as expected */
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qemu_thread_join(&thread);
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close(data.fd[0]);
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close(data.fd[1]);
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rfifolock_destroy(&data.lock);
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}
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int main(int argc, char **argv)
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{
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g_test_init(&argc, &argv, NULL);
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g_test_add_func("/nesting", test_nesting);
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g_test_add_func("/callback", test_callback);
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return g_test_run();
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}
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