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/typedefs.h" 19 #include "qemu/queue.h" 20 #include "qemu/timer.h" 21 22 /** 23 * Coroutines are a mechanism for stack switching and can be used for 24 * cooperative userspace threading. These functions provide a simple but 25 * useful flavor of coroutines that is suitable for writing sequential code, 26 * rather than callbacks, for operations that need to give up control while 27 * waiting for events to complete. 28 * 29 * These functions are re-entrant and may be used outside the global mutex. 30 */ 31 32 /** 33 * Mark a function that executes in coroutine context 34 * 35 * Functions that execute in coroutine context cannot be called directly from 36 * normal functions. In the future it would be nice to enable compiler or 37 * static checker support for catching such errors. This annotation might make 38 * it possible and in the meantime it serves as documentation. 39 * 40 * For example: 41 * 42 * static void coroutine_fn foo(void) { 43 * .... 44 * } 45 */ 46 #define coroutine_fn 47 48 typedef struct Coroutine Coroutine; 49 50 /** 51 * Coroutine entry point 52 * 53 * When the coroutine is entered for the first time, opaque is passed in as an 54 * argument. 55 * 56 * When this function returns, the coroutine is destroyed automatically and 57 * execution continues in the caller who last entered the coroutine. 58 */ 59 typedef void coroutine_fn CoroutineEntry(void *opaque); 60 61 /** 62 * Create a new coroutine 63 * 64 * Use qemu_coroutine_enter() to actually transfer control to the coroutine. 65 */ 66 Coroutine *qemu_coroutine_create(CoroutineEntry *entry); 67 68 /** 69 * Transfer control to a coroutine 70 * 71 * The opaque argument is passed as the argument to the entry point when 72 * entering the coroutine for the first time. It is subsequently ignored. 73 */ 74 void qemu_coroutine_enter(Coroutine *coroutine, void *opaque); 75 76 /** 77 * Transfer control back to a coroutine's caller 78 * 79 * This function does not return until the coroutine is re-entered using 80 * qemu_coroutine_enter(). 81 */ 82 void coroutine_fn qemu_coroutine_yield(void); 83 84 /** 85 * Get the currently executing coroutine 86 */ 87 Coroutine *coroutine_fn qemu_coroutine_self(void); 88 89 /** 90 * Return whether or not currently inside a coroutine 91 * 92 * This can be used to write functions that work both when in coroutine context 93 * and when not in coroutine context. Note that such functions cannot use the 94 * coroutine_fn annotation since they work outside coroutine context. 95 */ 96 bool qemu_in_coroutine(void); 97 98 99 100 /** 101 * CoQueues are a mechanism to queue coroutines in order to continue executing 102 * them later. They provide the fundamental primitives on which coroutine locks 103 * are built. 104 */ 105 typedef struct CoQueue { 106 QTAILQ_HEAD(, Coroutine) entries; 107 } CoQueue; 108 109 /** 110 * Initialise a CoQueue. This must be called before any other operation is used 111 * on the CoQueue. 112 */ 113 void qemu_co_queue_init(CoQueue *queue); 114 115 /** 116 * Adds the current coroutine to the CoQueue and transfers control to the 117 * caller of the coroutine. 118 */ 119 void coroutine_fn qemu_co_queue_wait(CoQueue *queue); 120 121 /** 122 * Restarts the next coroutine in the CoQueue and removes it from the queue. 123 * 124 * Returns true if a coroutine was restarted, false if the queue is empty. 125 */ 126 bool coroutine_fn qemu_co_queue_next(CoQueue *queue); 127 128 /** 129 * Restarts all coroutines in the CoQueue and leaves the queue empty. 130 */ 131 void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue); 132 133 /** 134 * Enter the next coroutine in the queue 135 */ 136 bool qemu_co_enter_next(CoQueue *queue); 137 138 /** 139 * Checks if the CoQueue is empty. 140 */ 141 bool qemu_co_queue_empty(CoQueue *queue); 142 143 144 /** 145 * Provides a mutex that can be used to synchronise coroutines 146 */ 147 typedef struct CoMutex { 148 bool locked; 149 CoQueue queue; 150 } CoMutex; 151 152 /** 153 * Initialises a CoMutex. This must be called before any other operation is used 154 * on the CoMutex. 155 */ 156 void qemu_co_mutex_init(CoMutex *mutex); 157 158 /** 159 * Locks the mutex. If the lock cannot be taken immediately, control is 160 * transferred to the caller of the current coroutine. 161 */ 162 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex); 163 164 /** 165 * Unlocks the mutex and schedules the next coroutine that was waiting for this 166 * lock to be run. 167 */ 168 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex); 169 170 typedef struct CoRwlock { 171 bool writer; 172 int reader; 173 CoQueue queue; 174 } CoRwlock; 175 176 /** 177 * Initialises a CoRwlock. This must be called before any other operation 178 * is used on the CoRwlock 179 */ 180 void qemu_co_rwlock_init(CoRwlock *lock); 181 182 /** 183 * Read locks the CoRwlock. If the lock cannot be taken immediately because 184 * of a parallel writer, control is transferred to the caller of the current 185 * coroutine. 186 */ 187 void qemu_co_rwlock_rdlock(CoRwlock *lock); 188 189 /** 190 * Write Locks the mutex. If the lock cannot be taken immediately because 191 * of a parallel reader, control is transferred to the caller of the current 192 * coroutine. 193 */ 194 void qemu_co_rwlock_wrlock(CoRwlock *lock); 195 196 /** 197 * Unlocks the read/write lock and schedules the next coroutine that was 198 * waiting for this lock to be run. 199 */ 200 void qemu_co_rwlock_unlock(CoRwlock *lock); 201 202 /** 203 * Yield the coroutine for a given duration 204 * 205 * Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be 206 * resumed when using aio_poll(). 207 */ 208 void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type, 209 int64_t ns); 210 211 /** 212 * Yield until a file descriptor becomes readable 213 * 214 * Note that this function clobbers the handlers for the file descriptor. 215 */ 216 void coroutine_fn yield_until_fd_readable(int fd); 217 218 #endif /* QEMU_COROUTINE_H */ 219