1/* 2 * QEMU coroutine implementation 3 * 4 * Copyright IBM, Corp. 2011 5 * 6 * Authors: 7 * Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> 8 * Kevin Wolf <kwolf@redhat.com> 9 * 10 * This work is licensed under the terms of the GNU LGPL, version 2 or later. 11 * See the COPYING.LIB file in the top-level directory. 12 * 13 */ 14 15#ifndef QEMU_COROUTINE_H 16#define QEMU_COROUTINE_H 17 18#include "qemu/queue.h" 19#include "qemu/timer.h" 20 21/** 22 * Coroutines are a mechanism for stack switching and can be used for 23 * cooperative userspace threading. These functions provide a simple but 24 * useful flavor of coroutines that is suitable for writing sequential code, 25 * rather than callbacks, for operations that need to give up control while 26 * waiting for events to complete. 27 * 28 * These functions are re-entrant and may be used outside the global mutex. 29 */ 30 31/** 32 * Mark a function that executes in coroutine context 33 * 34 * Functions that execute in coroutine context cannot be called directly from 35 * normal functions. In the future it would be nice to enable compiler or 36 * static checker support for catching such errors. This annotation might make 37 * it possible and in the meantime it serves as documentation. 38 * 39 * For example: 40 * 41 * static void coroutine_fn foo(void) { 42 * .... 43 * } 44 */ 45#define coroutine_fn 46 47typedef struct Coroutine Coroutine; 48 49/** 50 * Coroutine entry point 51 * 52 * When the coroutine is entered for the first time, opaque is passed in as an 53 * argument. 54 * 55 * When this function returns, the coroutine is destroyed automatically and 56 * execution continues in the caller who last entered the coroutine. 57 */ 58typedef void coroutine_fn CoroutineEntry(void *opaque); 59 60/** 61 * Create a new coroutine 62 * 63 * Use qemu_coroutine_enter() to actually transfer control to the coroutine. 64 * The opaque argument is passed as the argument to the entry point. 65 */ 66Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque); 67 68/** 69 * Transfer control to a coroutine 70 */ 71void qemu_coroutine_enter(Coroutine *coroutine); 72 73/** 74 * Transfer control back to a coroutine's caller 75 * 76 * This function does not return until the coroutine is re-entered using 77 * qemu_coroutine_enter(). 78 */ 79void coroutine_fn qemu_coroutine_yield(void); 80 81/** 82 * Get the currently executing coroutine 83 */ 84Coroutine *coroutine_fn qemu_coroutine_self(void); 85 86/** 87 * Return whether or not currently inside a coroutine 88 * 89 * This can be used to write functions that work both when in coroutine context 90 * and when not in coroutine context. Note that such functions cannot use the 91 * coroutine_fn annotation since they work outside coroutine context. 92 */ 93bool qemu_in_coroutine(void); 94 95/** 96 * Return true if the coroutine is currently entered 97 * 98 * A coroutine is "entered" if it has not yielded from the current 99 * qemu_coroutine_enter() call used to run it. This does not mean that the 100 * coroutine is currently executing code since it may have transferred control 101 * to another coroutine using qemu_coroutine_enter(). 102 * 103 * When several coroutines enter each other there may be no way to know which 104 * ones have already been entered. In such situations this function can be 105 * used to avoid recursively entering coroutines. 106 */ 107bool qemu_coroutine_entered(Coroutine *co); 108 109 110/** 111 * CoQueues are a mechanism to queue coroutines in order to continue executing 112 * them later. They provide the fundamental primitives on which coroutine locks 113 * are built. 114 */ 115typedef struct CoQueue { 116 QSIMPLEQ_HEAD(, Coroutine) entries; 117} CoQueue; 118 119/** 120 * Initialise a CoQueue. This must be called before any other operation is used 121 * on the CoQueue. 122 */ 123void qemu_co_queue_init(CoQueue *queue); 124 125/** 126 * Adds the current coroutine to the CoQueue and transfers control to the 127 * caller of the coroutine. 128 */ 129void coroutine_fn qemu_co_queue_wait(CoQueue *queue); 130 131/** 132 * Restarts the next coroutine in the CoQueue and removes it from the queue. 133 * 134 * Returns true if a coroutine was restarted, false if the queue is empty. 135 */ 136bool coroutine_fn qemu_co_queue_next(CoQueue *queue); 137 138/** 139 * Restarts all coroutines in the CoQueue and leaves the queue empty. 140 */ 141void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue); 142 143/** 144 * Enter the next coroutine in the queue 145 */ 146bool qemu_co_enter_next(CoQueue *queue); 147 148/** 149 * Checks if the CoQueue is empty. 150 */ 151bool qemu_co_queue_empty(CoQueue *queue); 152 153 154/** 155 * Provides a mutex that can be used to synchronise coroutines 156 */ 157typedef struct CoMutex { 158 bool locked; 159 Coroutine *holder; 160 CoQueue queue; 161} CoMutex; 162 163/** 164 * Initialises a CoMutex. This must be called before any other operation is used 165 * on the CoMutex. 166 */ 167void qemu_co_mutex_init(CoMutex *mutex); 168 169/** 170 * Locks the mutex. If the lock cannot be taken immediately, control is 171 * transferred to the caller of the current coroutine. 172 */ 173void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex); 174 175/** 176 * Unlocks the mutex and schedules the next coroutine that was waiting for this 177 * lock to be run. 178 */ 179void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex); 180 181typedef struct CoRwlock { 182 bool writer; 183 int reader; 184 CoQueue queue; 185} CoRwlock; 186 187/** 188 * Initialises a CoRwlock. This must be called before any other operation 189 * is used on the CoRwlock 190 */ 191void qemu_co_rwlock_init(CoRwlock *lock); 192 193/** 194 * Read locks the CoRwlock. If the lock cannot be taken immediately because 195 * of a parallel writer, control is transferred to the caller of the current 196 * coroutine. 197 */ 198void qemu_co_rwlock_rdlock(CoRwlock *lock); 199 200/** 201 * Write Locks the mutex. If the lock cannot be taken immediately because 202 * of a parallel reader, control is transferred to the caller of the current 203 * coroutine. 204 */ 205void qemu_co_rwlock_wrlock(CoRwlock *lock); 206 207/** 208 * Unlocks the read/write lock and schedules the next coroutine that was 209 * waiting for this lock to be run. 210 */ 211void qemu_co_rwlock_unlock(CoRwlock *lock); 212 213/** 214 * Yield the coroutine for a given duration 215 * 216 * Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be 217 * resumed when using aio_poll(). 218 */ 219void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type, 220 int64_t ns); 221 222/** 223 * Yield until a file descriptor becomes readable 224 * 225 * Note that this function clobbers the handlers for the file descriptor. 226 */ 227void coroutine_fn yield_until_fd_readable(int fd); 228 229#endif /* QEMU_COROUTINE_H */ 230