include/block/coroutine.h

   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 <stdbool.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     AioContext *ctx;
 108 } CoQueue;
 109
 110 /**
 111  * Initialise a CoQueue. This must be called before any other operation is used
 112  * on the CoQueue.
 113  */
 114 void qemu_co_queue_init(CoQueue *queue);
 115
 116 /**
 117  * Adds the current coroutine to the CoQueue and transfers control to the
 118  * caller of the coroutine.
 119  */
 120 void coroutine_fn qemu_co_queue_wait(CoQueue *queue);
 121
 122 /**
 123  * Adds the current coroutine to the head of the CoQueue and transfers control to the
 124  * caller of the coroutine.
 125  */
 126 void coroutine_fn qemu_co_queue_wait_insert_head(CoQueue *queue);
 127
 128 /**
 129  * Restarts the next coroutine in the CoQueue and removes it from the queue.
 130  *
 131  * Returns true if a coroutine was restarted, false if the queue is empty.
 132  */
 133 bool coroutine_fn qemu_co_queue_next(CoQueue *queue);
 134
 135 /**
 136  * Restarts all coroutines in the CoQueue and leaves the queue empty.
 137  */
 138 void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
 139
 140 /**
 141  * Enter the next coroutine in the queue
 142  */
 143 bool qemu_co_enter_next(CoQueue *queue);
 144
 145 /**
 146  * Checks if the CoQueue is empty.
 147  */
 148 bool qemu_co_queue_empty(CoQueue *queue);
 149
 150
 151 /**
 152  * Provides a mutex that can be used to synchronise coroutines
 153  */
 154 typedef struct CoMutex {
 155     bool locked;
 156     CoQueue queue;
 157 } CoMutex;
 158
 159 /**
 160  * Initialises a CoMutex. This must be called before any other operation is used
 161  * on the CoMutex.
 162  */
 163 void qemu_co_mutex_init(CoMutex *mutex);
 164
 165 /**
 166  * Locks the mutex. If the lock cannot be taken immediately, control is
 167  * transferred to the caller of the current coroutine.
 168  */
 169 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
 170
 171 /**
 172  * Unlocks the mutex and schedules the next coroutine that was waiting for this
 173  * lock to be run.
 174  */
 175 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
 176
 177 typedef struct CoRwlock {
 178     bool writer;
 179     int reader;
 180     CoQueue queue;
 181 } CoRwlock;
 182
 183 /**
 184  * Initialises a CoRwlock. This must be called before any other operation
 185  * is used on the CoRwlock
 186  */
 187 void qemu_co_rwlock_init(CoRwlock *lock);
 188
 189 /**
 190  * Read locks the CoRwlock. If the lock cannot be taken immediately because
 191  * of a parallel writer, control is transferred to the caller of the current
 192  * coroutine.
 193  */
 194 void qemu_co_rwlock_rdlock(CoRwlock *lock);
 195
 196 /**
 197  * Write Locks the mutex. If the lock cannot be taken immediately because
 198  * of a parallel reader, control is transferred to the caller of the current
 199  * coroutine.
 200  */
 201 void qemu_co_rwlock_wrlock(CoRwlock *lock);
 202
 203 /**
 204  * Unlocks the read/write lock and schedules the next coroutine that was
 205  * waiting for this lock to be run.
 206  */
 207 void qemu_co_rwlock_unlock(CoRwlock *lock);
 208
 209 /**
 210  * Yield the coroutine for a given duration
 211  *
 212  * Note this function uses timers and hence only works when a main loop is in
 213  * use.  See main-loop.h and do not use from qemu-tool programs.
 214  */
 215 void coroutine_fn co_sleep_ns(QEMUClock *clock, int64_t ns);
 216
 217 /**
 218  * Yield until a file descriptor becomes readable
 219  *
 220  * Note that this function clobbers the handlers for the file descriptor.
 221  */
 222 void coroutine_fn yield_until_fd_readable(int fd);
 223 #endif /* QEMU_COROUTINE_H */