1 /* 2 * AioContext wait support 3 * 4 * Copyright (C) 2018 Red Hat, Inc. 5 * 6 * Permission is hereby granted, free of charge, to any person obtaining a copy 7 * of this software and associated documentation files (the "Software"), to deal 8 * in the Software without restriction, including without limitation the rights 9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 10 * copies of the Software, and to permit persons to whom the Software is 11 * furnished to do so, subject to the following conditions: 12 * 13 * The above copyright notice and this permission notice shall be included in 14 * all copies or substantial portions of the Software. 15 * 16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 22 * THE SOFTWARE. 23 */ 24 25 #ifndef QEMU_AIO_WAIT_H 26 #define QEMU_AIO_WAIT_H 27 28 #include "block/aio.h" 29 30 /** 31 * AioWait: 32 * 33 * An object that facilitates synchronous waiting on a condition. The main 34 * loop can wait on an operation running in an IOThread as follows: 35 * 36 * AioWait *wait = ...; 37 * AioContext *ctx = ...; 38 * MyWork work = { .done = false }; 39 * schedule_my_work_in_iothread(ctx, &work); 40 * AIO_WAIT_WHILE(wait, ctx, !work.done); 41 * 42 * The IOThread must call aio_wait_kick() to notify the main loop when 43 * work.done changes: 44 * 45 * static void do_work(...) 46 * { 47 * ... 48 * work.done = true; 49 * aio_wait_kick(wait); 50 * } 51 */ 52 typedef struct { 53 /* Is the main loop waiting for a kick? Accessed with atomic ops. */ 54 bool need_kick; 55 } AioWait; 56 57 /** 58 * AIO_WAIT_WHILE: 59 * @wait: the aio wait object 60 * @ctx: the aio context 61 * @cond: wait while this conditional expression is true 62 * 63 * Wait while a condition is true. Use this to implement synchronous 64 * operations that require event loop activity. 65 * 66 * The caller must be sure that something calls aio_wait_kick() when the value 67 * of @cond might have changed. 68 * 69 * The caller's thread must be the IOThread that owns @ctx or the main loop 70 * thread (with @ctx acquired exactly once). This function cannot be used to 71 * wait on conditions between two IOThreads since that could lead to deadlock, 72 * go via the main loop instead. 73 */ 74 #define AIO_WAIT_WHILE(wait, ctx, cond) ({ \ 75 bool waited_ = false; \ 76 bool busy_ = true; \ 77 AioWait *wait_ = (wait); \ 78 AioContext *ctx_ = (ctx); \ 79 if (in_aio_context_home_thread(ctx_)) { \ 80 while ((cond) || busy_) { \ 81 busy_ = aio_poll(ctx_, (cond)); \ 82 waited_ |= !!(cond) | busy_; \ 83 } \ 84 } else { \ 85 assert(qemu_get_current_aio_context() == \ 86 qemu_get_aio_context()); \ 87 assert(!wait_->need_kick); \ 88 /* Set wait_->need_kick before evaluating cond. */ \ 89 atomic_mb_set(&wait_->need_kick, true); \ 90 while (busy_) { \ 91 if ((cond)) { \ 92 waited_ = busy_ = true; \ 93 aio_context_release(ctx_); \ 94 aio_poll(qemu_get_aio_context(), true); \ 95 aio_context_acquire(ctx_); \ 96 } else { \ 97 busy_ = aio_poll(ctx_, false); \ 98 waited_ |= busy_; \ 99 } \ 100 } \ 101 atomic_set(&wait_->need_kick, false); \ 102 } \ 103 waited_; }) 104 105 /** 106 * aio_wait_kick: 107 * @wait: the aio wait object that should re-evaluate its condition 108 * 109 * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During 110 * synchronous operations performed in an IOThread, the main thread lets the 111 * IOThread's event loop run, waiting for the operation to complete. A 112 * aio_wait_kick() call will wake up the main thread. 113 */ 114 void aio_wait_kick(AioWait *wait); 115 116 #endif /* QEMU_AIO_WAIT */ 117