[Qemu-devel] [PATCH 19/40] aio: convert from RFifoLock to QemuRecMutex

[Paolo Bonzini <pbonzini@redhat.com>]

It is simpler and a bit faster, and QEMU does not need the contention
callbacks (and thus the fairness) anymore.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 async.c                  |  8 ++---
 include/block/aio.h      |  3 +-
 include/qemu/rfifolock.h | 54 ----------------------------
 tests/.gitignore         |  1 -
 tests/Makefile           |  2 --
 tests/test-rfifolock.c   | 91 ------------------------------------------------
 util/Makefile.objs       |  1 -
 util/rfifolock.c         | 78 -----------------------------------------
 8 files changed, 5 insertions(+), 233 deletions(-)
 delete mode 100644 include/qemu/rfifolock.h
 delete mode 100644 tests/test-rfifolock.c
 delete mode 100644 util/rfifolock.c

diff --git a/async.c b/async.c
index f70d23a..567c3b9 100644
--- a/async.c
+++ b/async.c
@@ -253,7 +253,7 @@ aio_ctx_finalize(GSource     *source)
 
     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL);
     event_notifier_cleanup(&ctx->notifier);
-    rfifolock_destroy(&ctx->lock);
+    qemu_rec_mutex_destroy(&ctx->lock);
     qemu_mutex_destroy(&ctx->bh_lock);
     timerlistgroup_deinit(&ctx->tlg);
 }
@@ -331,7 +331,7 @@ AioContext *aio_context_new(Error **errp)
                            event_notifier_dummy_cb);
     ctx->thread_pool = NULL;
     qemu_mutex_init(&ctx->bh_lock);
-    rfifolock_init(&ctx->lock, NULL, NULL);
+    qemu_rec_mutex_init(&ctx->lock);
     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 
     return ctx;
@@ -352,10 +352,10 @@ void aio_context_unref(AioContext *ctx)
 
 void aio_context_acquire(AioContext *ctx)
 {
-    rfifolock_lock(&ctx->lock);
+    qemu_rec_mutex_lock(&ctx->lock);
 }
 
 void aio_context_release(AioContext *ctx)
 {
-    rfifolock_unlock(&ctx->lock);
+    qemu_rec_mutex_unlock(&ctx->lock);
 }
diff --git a/include/block/aio.h b/include/block/aio.h
index b41e291..b416621 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -19,7 +19,6 @@
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
 #include "qemu/thread.h"
-#include "qemu/rfifolock.h"
 #include "qemu/timer.h"
 
 typedef struct BlockAIOCB BlockAIOCB;
@@ -52,7 +51,7 @@ struct AioContext {
     GSource source;
 
     /* Protects all fields from multi-threaded access */
-    RFifoLock lock;
+    QemuRecMutex lock;
 
     /* The list of registered AIO handlers */
     QLIST_HEAD(, AioHandler) aio_handlers;
diff --git a/include/qemu/rfifolock.h b/include/qemu/rfifolock.h
deleted file mode 100644
index b23ab53..0000000
--- a/include/qemu/rfifolock.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- * 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/.gitignore b/tests/.gitignore
index 1e55722..850d64e 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -41,7 +41,6 @@ test-qmp-introspect.[ch]
 test-qmp-marshal.c
 test-qmp-output-visitor
 test-rcu-list
-test-rfifolock
 test-string-input-visitor
 test-string-output-visitor
 test-thread-pool
diff --git a/tests/Makefile b/tests/Makefile
index b937984..135bf5f 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -39,7 +39,6 @@ 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$(EXESUF)
-check-unit-$(CONFIG_POSIX) += 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
@@ -392,7 +391,6 @@ tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o $(test-qom-obj-y
 tests/check-qom-proplist$(EXESUF): tests/check-qom-proplist.o $(test-qom-obj-y)
 tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(test-block-obj-y)
 tests/test-aio$(EXESUF): tests/test-aio.o $(test-block-obj-y)
-tests/test-rfifolock$(EXESUF): tests/test-rfifolock.o $(test-util-obj-y)
 tests/test-throttle$(EXESUF): tests/test-throttle.o $(test-block-obj-y)
 tests/test-blockjob-txn$(EXESUF): tests/test-blockjob-txn.o $(test-block-obj-y) $(test-util-obj-y)
 tests/test-thread-pool$(EXESUF): tests/test-thread-pool.o $(test-block-obj-y)
diff --git a/tests/test-rfifolock.c b/tests/test-rfifolock.c
deleted file mode 100644
index 0572ebb..0000000
--- a/tests/test-rfifolock.c
+++ /dev/null
@@ -1,91 +0,0 @@
-/*
- * 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 89dd80e..f536cc8 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -23,7 +23,6 @@ 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
 util-obj-y += rcu.o
 util-obj-y += qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o
 util-obj-y += qemu-coroutine-sleep.o
diff --git a/util/rfifolock.c b/util/rfifolock.c
deleted file mode 100644
index afbf748..0000000
--- a/util/rfifolock.c
+++ /dev/null
@@ -1,78 +0,0 @@
-/*
- * 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);
-}
-- 
1.8.3.1