From 98563fc3ec44c1becce6f1720ad6b0a82ed101b4 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 3 Mar 2014 11:30:04 +0100 Subject: aio: add aio_context_acquire() and aio_context_release() It can be useful to run an AioContext from a thread which normally does not "own" the AioContext. For example, request draining can be implemented by acquiring the AioContext and looping aio_poll() until all requests have been completed. The following pattern should work: /* Event loop thread */ while (running) { aio_context_acquire(ctx); aio_poll(ctx, true); aio_context_release(ctx); } /* Another thread */ aio_context_acquire(ctx); bdrv_read(bs, 0x1000, buf, 1); aio_context_release(ctx); This patch implements aio_context_acquire() and aio_context_release(). Note that existing aio_poll() callers do not need to worry about acquiring and releasing - it is only needed when multiple threads will call aio_poll() on the same AioContext. Signed-off-by: Stefan Hajnoczi --- include/block/aio.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'include/block/aio.h') diff --git a/include/block/aio.h b/include/block/aio.h index 2efdf416cf..a92511bd3b 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -19,6 +19,7 @@ #include "qemu/queue.h" #include "qemu/event_notifier.h" #include "qemu/thread.h" +#include "qemu/rfifolock.h" #include "qemu/timer.h" typedef struct BlockDriverAIOCB BlockDriverAIOCB; @@ -47,6 +48,9 @@ typedef void IOHandler(void *opaque); struct AioContext { GSource source; + /* Protects all fields from multi-threaded access */ + RFifoLock lock; + /* The list of registered AIO handlers */ QLIST_HEAD(, AioHandler) aio_handlers; @@ -104,6 +108,20 @@ void aio_context_ref(AioContext *ctx); */ void aio_context_unref(AioContext *ctx); +/* Take ownership of the AioContext. If the AioContext will be shared between + * threads, a thread must have ownership when calling aio_poll(). + * + * Note that multiple threads calling aio_poll() means timers, BHs, and + * callbacks may be invoked from a different thread than they were registered + * from. Therefore, code must use AioContext acquire/release or use + * fine-grained synchronization to protect shared state if other threads will + * be accessing it simultaneously. + */ +void aio_context_acquire(AioContext *ctx); + +/* Relinquish ownership of the AioContext. */ +void aio_context_release(AioContext *ctx); + /** * aio_bh_new: Allocate a new bottom half structure. * -- cgit v1.2.3