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/typedefs.h"
  20 #include "qemu/queue.h"
  21 #include "qemu/timer.h"
  22
  23 /**
  24  * Coroutines are a mechanism for stack switching and can be used for
  25  * cooperative userspace threading.  These functions provide a simple but
  26  * useful flavor of coroutines that is suitable for writing sequential code,
  27  * rather than callbacks, for operations that need to give up control while
  28  * waiting for events to complete.
  29  *
  30  * These functions are re-entrant and may be used outside the global mutex.
  31  */
  32
  33 /**
  34  * Mark a function that executes in coroutine context
  35  *
  36  * Functions that execute in coroutine context cannot be called directly from
  37  * normal functions.  In the future it would be nice to enable compiler or
  38  * static checker support for catching such errors.  This annotation might make
  39  * it possible and in the meantime it serves as documentation.
  40  *
  41  * For example:
  42  *
  43  *   static void coroutine_fn foo(void) {
  44  *       ....
  45  *   }
  46  */
  47 #define coroutine_fn
  48
  49 typedef struct Coroutine Coroutine;
  50
  51 /**
  52  * Coroutine entry point
  53  *
  54  * When the coroutine is entered for the first time, opaque is passed in as an
  55  * argument.
  56  *
  57  * When this function returns, the coroutine is destroyed automatically and
  58  * execution continues in the caller who last entered the coroutine.
  59  */
  60 typedef void coroutine_fn CoroutineEntry(void *opaque);
  61
  62 /**
  63  * Create a new coroutine
  64  *
  65  * Use qemu_coroutine_enter() to actually transfer control to the coroutine.
  66  */
  67 Coroutine *qemu_coroutine_create(CoroutineEntry *entry);
  68
  69 /**
  70  * Transfer control to a coroutine
  71  *
  72  * The opaque argument is passed as the argument to the entry point when
  73  * entering the coroutine for the first time.  It is subsequently ignored.
  74  */
  75 void qemu_coroutine_enter(Coroutine *coroutine, void *opaque);
  76
  77 /**
  78  * Transfer control back to a coroutine's caller
  79  *
  80  * This function does not return until the coroutine is re-entered using
  81  * qemu_coroutine_enter().
  82  */
  83 void coroutine_fn qemu_coroutine_yield(void);
  84
  85 /**
  86  * Get the currently executing coroutine
  87  */
  88 Coroutine *coroutine_fn qemu_coroutine_self(void);
  89
  90 /**
  91  * Return whether or not currently inside a coroutine
  92  *
  93  * This can be used to write functions that work both when in coroutine context
  94  * and when not in coroutine context.  Note that such functions cannot use the
  95  * coroutine_fn annotation since they work outside coroutine context.
  96  */
  97 bool qemu_in_coroutine(void);
  98
  99
 100
 101 /**
 102  * CoQueues are a mechanism to queue coroutines in order to continue executing
 103  * them later. They provide the fundamental primitives on which coroutine locks
 104  * are built.
 105  */
 106 typedef struct CoQueue {
 107     QTAILQ_HEAD(, Coroutine) entries;
 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  * Restarts the next coroutine in the CoQueue and removes it from the queue.
 124  *
 125  * Returns true if a coroutine was restarted, false if the queue is empty.
 126  */
 127 bool coroutine_fn qemu_co_queue_next(CoQueue *queue);
 128
 129 /**
 130  * Restarts all coroutines in the CoQueue and leaves the queue empty.
 131  */
 132 void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
 133
 134 /**
 135  * Enter the next coroutine in the queue
 136  */
 137 bool qemu_co_enter_next(CoQueue *queue);
 138
 139 /**
 140  * Checks if the CoQueue is empty.
 141  */
 142 bool qemu_co_queue_empty(CoQueue *queue);
 143
 144
 145 /**
 146  * Provides a mutex that can be used to synchronise coroutines
 147  */
 148 typedef struct CoMutex {
 149     bool locked;
 150     CoQueue queue;
 151 } CoMutex;
 152
 153 /**
 154  * Initialises a CoMutex. This must be called before any other operation is used
 155  * on the CoMutex.
 156  */
 157 void qemu_co_mutex_init(CoMutex *mutex);
 158
 159 /**
 160  * Locks the mutex. If the lock cannot be taken immediately, control is
 161  * transferred to the caller of the current coroutine.
 162  */
 163 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
 164
 165 /**
 166  * Unlocks the mutex and schedules the next coroutine that was waiting for this
 167  * lock to be run.
 168  */
 169 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
 170
 171 typedef struct CoRwlock {
 172     bool writer;
 173     int reader;
 174     CoQueue queue;
 175 } CoRwlock;
 176
 177 /**
 178  * Initialises a CoRwlock. This must be called before any other operation
 179  * is used on the CoRwlock
 180  */
 181 void qemu_co_rwlock_init(CoRwlock *lock);
 182
 183 /**
 184  * Read locks the CoRwlock. If the lock cannot be taken immediately because
 185  * of a parallel writer, control is transferred to the caller of the current
 186  * coroutine.
 187  */
 188 void qemu_co_rwlock_rdlock(CoRwlock *lock);
 189
 190 /**
 191  * Write Locks the mutex. If the lock cannot be taken immediately because
 192  * of a parallel reader, control is transferred to the caller of the current
 193  * coroutine.
 194  */
 195 void qemu_co_rwlock_wrlock(CoRwlock *lock);
 196
 197 /**
 198  * Unlocks the read/write lock and schedules the next coroutine that was
 199  * waiting for this lock to be run.
 200  */
 201 void qemu_co_rwlock_unlock(CoRwlock *lock);
 202
 203 /**
 204  * Yield the coroutine for a given duration
 205  *
 206  * Note this function uses timers and hence only works when a main loop is in
 207  * use.  See main-loop.h and do not use from qemu-tool programs.
 208  */
 209 void coroutine_fn co_sleep_ns(QEMUClockType type, int64_t ns);
 210
 211 /**
 212  * Yield the coroutine for a given duration
 213  *
 214  * Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be
 215  * resumed when using qemu_aio_wait().
 216  */
 217 void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type,
 218                                   int64_t ns);
 219
 220 /**
 221  * Yield until a file descriptor becomes readable
 222  *
 223  * Note that this function clobbers the handlers for the file descriptor.
 224  */
 225 void coroutine_fn yield_until_fd_readable(int fd);
 226 #endif /* QEMU_COROUTINE_H */