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 */ 65Coroutine *qemu_coroutine_create(CoroutineEntry *entry); 66 67/** 68 * Transfer control to a coroutine 69 * 70 * The opaque argument is passed as the argument to the entry point when 71 * entering the coroutine for the first time. It is subsequently ignored. 72 */ 73void qemu_coroutine_enter(Coroutine *coroutine, void *opaque); 74 75/** 76 * Transfer control back to a coroutine's caller 77 * 78 * This function does not return until the coroutine is re-entered using 79 * qemu_coroutine_enter(). 80 */ 81void coroutine_fn qemu_coroutine_yield(void); 82 83/** 84 * Get the currently executing coroutine 85 */ 86Coroutine *coroutine_fn qemu_coroutine_self(void); 87 88/** 89 * Return whether or not currently inside a coroutine 90 * 91 * This can be used to write functions that work both when in coroutine context 92 * and when not in coroutine context. Note that such functions cannot use the 93 * coroutine_fn annotation since they work outside coroutine context. 94 */ 95bool qemu_in_coroutine(void); 96 97 98 99/** 100 * CoQueues are a mechanism to queue coroutines in order to continue executing 101 * them later. They provide the fundamental primitives on which coroutine locks 102 * are built. 103 */ 104typedef struct CoQueue { 105 QTAILQ_HEAD(, Coroutine) entries; 106} CoQueue; 107 108/** 109 * Initialise a CoQueue. This must be called before any other operation is used 110 * on the CoQueue. 111 */ 112void qemu_co_queue_init(CoQueue *queue); 113 114/** 115 * Adds the current coroutine to the CoQueue and transfers control to the 116 * caller of the coroutine. 117 */ 118void coroutine_fn qemu_co_queue_wait(CoQueue *queue); 119 120/** 121 * Restarts the next coroutine in the CoQueue and removes it from the queue. 122 * 123 * Returns true if a coroutine was restarted, false if the queue is empty. 124 */ 125bool coroutine_fn qemu_co_queue_next(CoQueue *queue); 126 127/** 128 * Restarts all coroutines in the CoQueue and leaves the queue empty. 129 */ 130void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue); 131 132/** 133 * Enter the next coroutine in the queue 134 */ 135bool qemu_co_enter_next(CoQueue *queue); 136 137/** 138 * Checks if the CoQueue is empty. 139 */ 140bool qemu_co_queue_empty(CoQueue *queue); 141 142 143/** 144 * Provides a mutex that can be used to synchronise coroutines 145 */ 146typedef struct CoMutex { 147 bool locked; 148 CoQueue queue; 149} CoMutex; 150 151/** 152 * Initialises a CoMutex. This must be called before any other operation is used 153 * on the CoMutex. 154 */ 155void qemu_co_mutex_init(CoMutex *mutex); 156 157/** 158 * Locks the mutex. If the lock cannot be taken immediately, control is 159 * transferred to the caller of the current coroutine. 160 */ 161void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex); 162 163/** 164 * Unlocks the mutex and schedules the next coroutine that was waiting for this 165 * lock to be run. 166 */ 167void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex); 168 169typedef struct CoRwlock { 170 bool writer; 171 int reader; 172 CoQueue queue; 173} CoRwlock; 174 175/** 176 * Initialises a CoRwlock. This must be called before any other operation 177 * is used on the CoRwlock 178 */ 179void qemu_co_rwlock_init(CoRwlock *lock); 180 181/** 182 * Read locks the CoRwlock. If the lock cannot be taken immediately because 183 * of a parallel writer, control is transferred to the caller of the current 184 * coroutine. 185 */ 186void qemu_co_rwlock_rdlock(CoRwlock *lock); 187 188/** 189 * Write Locks the mutex. If the lock cannot be taken immediately because 190 * of a parallel reader, control is transferred to the caller of the current 191 * coroutine. 192 */ 193void qemu_co_rwlock_wrlock(CoRwlock *lock); 194 195/** 196 * Unlocks the read/write lock and schedules the next coroutine that was 197 * waiting for this lock to be run. 198 */ 199void qemu_co_rwlock_unlock(CoRwlock *lock); 200 201/** 202 * Yield the coroutine for a given duration 203 * 204 * Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be 205 * resumed when using aio_poll(). 206 */ 207void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type, 208 int64_t ns); 209 210/** 211 * Yield until a file descriptor becomes readable 212 * 213 * Note that this function clobbers the handlers for the file descriptor. 214 */ 215void coroutine_fn yield_until_fd_readable(int fd); 216 217#endif /* QEMU_COROUTINE_H */ 218