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