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Diffstat (limited to 'include/block/aio-wait.h')
| -rw-r--r-- | include/block/aio-wait.h | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h new file mode 100644 index 0000000000..a48c744fa8 --- /dev/null +++ b/include/block/aio-wait.h @@ -0,0 +1,116 @@ +/* + * AioContext wait support + * + * Copyright (C) 2018 Red Hat, Inc. + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ + +#ifndef QEMU_AIO_WAIT_H +#define QEMU_AIO_WAIT_H + +#include "block/aio.h" + +/** + * AioWait: + * + * An object that facilitates synchronous waiting on a condition. The main + * loop can wait on an operation running in an IOThread as follows: + * + * AioWait *wait = ...; + * AioContext *ctx = ...; + * MyWork work = { .done = false }; + * schedule_my_work_in_iothread(ctx, &work); + * AIO_WAIT_WHILE(wait, ctx, !work.done); + * + * The IOThread must call aio_wait_kick() to notify the main loop when + * work.done changes: + * + * static void do_work(...) + * { + * ... + * work.done = true; + * aio_wait_kick(wait); + * } + */ +typedef struct { + /* Is the main loop waiting for a kick? Accessed with atomic ops. */ + bool need_kick; +} AioWait; + +/** + * AIO_WAIT_WHILE: + * @wait: the aio wait object + * @ctx: the aio context + * @cond: wait while this conditional expression is true + * + * Wait while a condition is true. Use this to implement synchronous + * operations that require event loop activity. + * + * The caller must be sure that something calls aio_wait_kick() when the value + * of @cond might have changed. + * + * The caller's thread must be the IOThread that owns @ctx or the main loop + * thread (with @ctx acquired exactly once). This function cannot be used to + * wait on conditions between two IOThreads since that could lead to deadlock, + * go via the main loop instead. + */ +#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \ + bool waited_ = false; \ + bool busy_ = true; \ + AioWait *wait_ = (wait); \ + AioContext *ctx_ = (ctx); \ + if (in_aio_context_home_thread(ctx_)) { \ + while ((cond) || busy_) { \ + busy_ = aio_poll(ctx_, (cond)); \ + waited_ |= !!(cond) | busy_; \ + } \ + } else { \ + assert(qemu_get_current_aio_context() == \ + qemu_get_aio_context()); \ + assert(!wait_->need_kick); \ + /* Set wait_->need_kick before evaluating cond. */ \ + atomic_mb_set(&wait_->need_kick, true); \ + while (busy_) { \ + if ((cond)) { \ + waited_ = busy_ = true; \ + aio_context_release(ctx_); \ + aio_poll(qemu_get_aio_context(), true); \ + aio_context_acquire(ctx_); \ + } else { \ + busy_ = aio_poll(ctx_, false); \ + waited_ |= busy_; \ + } \ + } \ + atomic_set(&wait_->need_kick, false); \ + } \ + waited_; }) + +/** + * aio_wait_kick: + * @wait: the aio wait object that should re-evaluate its condition + * + * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During + * synchronous operations performed in an IOThread, the main thread lets the + * IOThread's event loop run, waiting for the operation to complete. A + * aio_wait_kick() call will wake up the main thread. + */ +void aio_wait_kick(AioWait *wait); + +#endif /* QEMU_AIO_WAIT */ |