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