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author | fishsoupisgood <github@madingley.org> | 2019-04-29 01:17:54 +0100 |
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committer | fishsoupisgood <github@madingley.org> | 2019-05-27 03:43:43 +0100 |
commit | 3f2546b2ef55b661fd8dd69682b38992225e86f6 (patch) | |
tree | 65ca85f13617aee1dce474596800950f266a456c /util/rfifolock.c | |
download | qemu-master.tar.gz qemu-master.tar.bz2 qemu-master.zip |
Diffstat (limited to 'util/rfifolock.c')
-rw-r--r-- | util/rfifolock.c | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/util/rfifolock.c b/util/rfifolock.c new file mode 100644 index 00000000..afbf7488 --- /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); +} |