diff options
| -rw-r--r-- | include/qemu/rfifolock.h | 54 | ||||
| -rw-r--r-- | tests/Makefile | 2 | ||||
| -rw-r--r-- | tests/test-rfifolock.c | 91 | ||||
| -rw-r--r-- | util/Makefile.objs | 1 | ||||
| -rw-r--r-- | util/rfifolock.c | 78 |
5 files changed, 226 insertions, 0 deletions
diff --git a/include/qemu/rfifolock.h b/include/qemu/rfifolock.h new file mode 100644 index 0000000000..b23ab538a6 --- /dev/null +++ b/include/qemu/rfifolock.h @@ -0,0 +1,54 @@ +/* + * Recursive FIFO lock + * + * Copyright Red Hat, Inc. 2013 + * + * Authors: + * Stefan Hajnoczi <stefanha@redhat.com> + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + * + */ + +#ifndef QEMU_RFIFOLOCK_H +#define QEMU_RFIFOLOCK_H + +#include "qemu/thread.h" + +/* Recursive FIFO lock + * + * This lock provides more features than a plain mutex: + * + * 1. Fairness - enforces FIFO order. + * 2. Nesting - can be taken recursively. + * 3. Contention callback - optional, called when thread must wait. + * + * The recursive FIFO lock is heavyweight so prefer other synchronization + * primitives if you do not need its features. + */ +typedef struct { + QemuMutex lock; /* protects all fields */ + + /* FIFO order */ + unsigned int head; /* active ticket number */ + unsigned int tail; /* waiting ticket number */ + QemuCond cond; /* used to wait for our ticket number */ + + /* Nesting */ + QemuThread owner_thread; /* thread that currently has ownership */ + unsigned int nesting; /* amount of nesting levels */ + + /* Contention callback */ + void (*cb)(void *); /* called when thread must wait, with ->lock + * held so it may not recursively lock/unlock + */ + void *cb_opaque; +} RFifoLock; + +void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque); +void rfifolock_destroy(RFifoLock *r); +void rfifolock_lock(RFifoLock *r); +void rfifolock_unlock(RFifoLock *r); + +#endif /* QEMU_RFIFOLOCK_H */ diff --git a/tests/Makefile b/tests/Makefile index e146f81d44..190e596689 100644 --- a/tests/Makefile +++ b/tests/Makefile @@ -35,6 +35,7 @@ check-unit-y += tests/test-visitor-serialization$(EXESUF) check-unit-y += tests/test-iov$(EXESUF) gcov-files-test-iov-y = util/iov.c check-unit-y += tests/test-aio$(EXESUF) +check-unit-y += tests/test-rfifolock$(EXESUF) check-unit-y += tests/test-throttle$(EXESUF) gcov-files-test-aio-$(CONFIG_WIN32) = aio-win32.c gcov-files-test-aio-$(CONFIG_POSIX) = aio-posix.c @@ -176,6 +177,7 @@ tests/check-qjson$(EXESUF): tests/check-qjson.o libqemuutil.a libqemustub.a tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o $(qom-core-obj) libqemuutil.a libqemustub.a tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(block-obj-y) libqemuutil.a libqemustub.a tests/test-aio$(EXESUF): tests/test-aio.o $(block-obj-y) libqemuutil.a libqemustub.a +tests/test-rfifolock$(EXESUF): tests/test-rfifolock.o libqemuutil.a libqemustub.a tests/test-throttle$(EXESUF): tests/test-throttle.o $(block-obj-y) libqemuutil.a libqemustub.a tests/test-thread-pool$(EXESUF): tests/test-thread-pool.o $(block-obj-y) libqemuutil.a libqemustub.a tests/test-iov$(EXESUF): tests/test-iov.o libqemuutil.a diff --git a/tests/test-rfifolock.c b/tests/test-rfifolock.c new file mode 100644 index 0000000000..0572ebb42a --- /dev/null +++ b/tests/test-rfifolock.c @@ -0,0 +1,91 @@ +/* + * RFifoLock tests + * + * Copyright Red Hat, Inc. 2013 + * + * Authors: + * Stefan Hajnoczi <stefanha@redhat.com> + * + * This work is licensed under the terms of the GNU LGPL, version 2 or later. + * See the COPYING.LIB file in the top-level directory. + */ + +#include <glib.h> +#include "qemu-common.h" +#include "qemu/rfifolock.h" + +static void test_nesting(void) +{ + RFifoLock lock; + + /* Trivial test, ensure the lock is recursive */ + rfifolock_init(&lock, NULL, NULL); + rfifolock_lock(&lock); + rfifolock_lock(&lock); + rfifolock_lock(&lock); + rfifolock_unlock(&lock); + rfifolock_unlock(&lock); + rfifolock_unlock(&lock); + rfifolock_destroy(&lock); +} + +typedef struct { + RFifoLock lock; + int fd[2]; +} CallbackTestData; + +static void rfifolock_cb(void *opaque) +{ + CallbackTestData *data = opaque; + int ret; + char c = 0; + + ret = write(data->fd[1], &c, sizeof(c)); + g_assert(ret == 1); +} + +static void *callback_thread(void *opaque) +{ + CallbackTestData *data = opaque; + + /* The other thread holds the lock so the contention callback will be + * invoked... + */ + rfifolock_lock(&data->lock); + rfifolock_unlock(&data->lock); + return NULL; +} + +static void test_callback(void) +{ + CallbackTestData data; + QemuThread thread; + int ret; + char c; + + rfifolock_init(&data.lock, rfifolock_cb, &data); + ret = qemu_pipe(data.fd); + g_assert(ret == 0); + + /* Hold lock but allow the callback to kick us by writing to the pipe */ + rfifolock_lock(&data.lock); + qemu_thread_create(&thread, "callback_thread", + callback_thread, &data, QEMU_THREAD_JOINABLE); + ret = read(data.fd[0], &c, sizeof(c)); + g_assert(ret == 1); + rfifolock_unlock(&data.lock); + /* If we got here then the callback was invoked, as expected */ + + qemu_thread_join(&thread); + close(data.fd[0]); + close(data.fd[1]); + rfifolock_destroy(&data.lock); +} + +int main(int argc, char **argv) +{ + g_test_init(&argc, &argv, NULL); + g_test_add_func("/nesting", test_nesting); + g_test_add_func("/callback", test_callback); + return g_test_run(); +} diff --git a/util/Makefile.objs b/util/Makefile.objs index 937376b082..df83b629a0 100644 --- a/util/Makefile.objs +++ b/util/Makefile.objs @@ -14,3 +14,4 @@ util-obj-y += crc32c.o util-obj-y += throttle.o util-obj-y += getauxval.o util-obj-y += readline.o +util-obj-y += rfifolock.o diff --git a/util/rfifolock.c b/util/rfifolock.c new file mode 100644 index 0000000000..afbf7488df --- /dev/null +++ b/util/rfifolock.c @@ -0,0 +1,78 @@ +/* + * Recursive FIFO lock + * + * Copyright Red Hat, Inc. 2013 + * + * Authors: + * Stefan Hajnoczi <stefanha@redhat.com> + * + * This work is licensed under the terms of the GNU LGPL, version 2 or later. + * See the COPYING.LIB file in the top-level directory. + * + */ + +#include <assert.h> +#include "qemu/rfifolock.h" + +void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque) +{ + qemu_mutex_init(&r->lock); + r->head = 0; + r->tail = 0; + qemu_cond_init(&r->cond); + r->nesting = 0; + r->cb = cb; + r->cb_opaque = opaque; +} + +void rfifolock_destroy(RFifoLock *r) +{ + qemu_cond_destroy(&r->cond); + qemu_mutex_destroy(&r->lock); +} + +/* + * Theory of operation: + * + * In order to ensure FIFO ordering, implement a ticketlock. Threads acquiring + * the lock enqueue themselves by incrementing the tail index. When the lock + * is unlocked, the head is incremented and waiting threads are notified. + * + * Recursive locking does not take a ticket since the head is only incremented + * when the outermost recursive caller unlocks. + */ +void rfifolock_lock(RFifoLock *r) +{ + qemu_mutex_lock(&r->lock); + + /* Take a ticket */ + unsigned int ticket = r->tail++; + + if (r->nesting > 0 && qemu_thread_is_self(&r->owner_thread)) { + r->tail--; /* put ticket back, we're nesting */ + } else { + while (ticket != r->head) { + /* Invoke optional contention callback */ + if (r->cb) { + r->cb(r->cb_opaque); + } + qemu_cond_wait(&r->cond, &r->lock); + } + } + + qemu_thread_get_self(&r->owner_thread); + r->nesting++; + qemu_mutex_unlock(&r->lock); +} + +void rfifolock_unlock(RFifoLock *r) +{ + qemu_mutex_lock(&r->lock); + assert(r->nesting > 0); + assert(qemu_thread_is_self(&r->owner_thread)); + if (--r->nesting == 0) { + r->head++; + qemu_cond_broadcast(&r->cond); + } + qemu_mutex_unlock(&r->lock); +} |