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 /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */ 54 unsigned num_waiters; 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 /* Increment wait_->num_waiters before evaluating cond. */ \ 88 atomic_inc(&wait_->num_waiters); \ 89 while (busy_) { \ 90 if ((cond)) { \ 91 waited_ = busy_ = true; \ 92 aio_context_release(ctx_); \ 93 aio_poll(qemu_get_aio_context(), true); \ 94 aio_context_acquire(ctx_); \ 95 } else { \ 96 busy_ = aio_poll(ctx_, false); \ 97 waited_ |= busy_; \ 98 } \ 99 } \ 100 atomic_dec(&wait_->num_waiters); \ 101 } \ 102 waited_; }) 103 104 /** 105 * aio_wait_kick: 106 * @wait: the aio wait object that should re-evaluate its condition 107 * 108 * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During 109 * synchronous operations performed in an IOThread, the main thread lets the 110 * IOThread's event loop run, waiting for the operation to complete. A 111 * aio_wait_kick() call will wake up the main thread. 112 */ 113 void aio_wait_kick(AioWait *wait); 114 115 /** 116 * aio_wait_bh_oneshot: 117 * @ctx: the aio context 118 * @cb: the BH callback function 119 * @opaque: user data for the BH callback function 120 * 121 * Run a BH in @ctx and wait for it to complete. 122 * 123 * Must be called from the main loop thread with @ctx acquired exactly once. 124 * Note that main loop event processing may occur. 125 */ 126 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 127 128 #endif /* QEMU_AIO_WAIT */ 129