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 <stdbool.h>
  19 #include "qemu-queue.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  */
  65 Coroutine *qemu_coroutine_create(CoroutineEntry *entry);
  66
  67 /**
  68  * Transfer control to a coroutine
  69  *
  70  * The opaque argument is passed as the argument to the entry point when
  71  * entering the coroutine for the first time.  It is subsequently ignored.
  72  */
  73 void qemu_coroutine_enter(Coroutine *coroutine, void *opaque);
  74
  75 /**
  76  * Transfer control back to a coroutine's caller
  77  *
  78  * This function does not return until the coroutine is re-entered using
  79  * qemu_coroutine_enter().
  80  */
  81 void coroutine_fn qemu_coroutine_yield(void);
  82
  83 /**
  84  * Get the currently executing coroutine
  85  */
  86 Coroutine *coroutine_fn qemu_coroutine_self(void);
  87
  88 /**
  89  * Return whether or not currently inside a coroutine
  90  *
  91  * This can be used to write functions that work both when in coroutine context
  92  * and when not in coroutine context.  Note that such functions cannot use the
  93  * coroutine_fn annotation since they work outside coroutine context.
  94  */
  95 bool qemu_in_coroutine(void);
  96
  97
  98
  99 /**
 100  * CoQueues are a mechanism to queue coroutines in order to continue executing
 101  * them later. They provide the fundamental primitives on which coroutine locks
 102  * are built.
 103  */
 104 typedef struct CoQueue {
 105     QTAILQ_HEAD(, Coroutine) entries;
 106 } CoQueue;
 107
 108 /**
 109  * Initialise a CoQueue. This must be called before any other operation is used
 110  * on the CoQueue.
 111  */
 112 void qemu_co_queue_init(CoQueue *queue);
 113
 114 /**
 115  * Adds the current coroutine to the CoQueue and transfers control to the
 116  * caller of the coroutine.
 117  */
 118 void coroutine_fn qemu_co_queue_wait(CoQueue *queue);
 119
 120 /**
 121  * Restarts the next coroutine in the CoQueue and removes it from the queue.
 122  *
 123  * Returns true if a coroutine was restarted, false if the queue is empty.
 124  */
 125 bool qemu_co_queue_next(CoQueue *queue);
 126
 127 /**
 128  * Checks if the CoQueue is empty.
 129  */
 130 bool qemu_co_queue_empty(CoQueue *queue);
 131
 132
 133 /**
 134  * Provides a mutex that can be used to synchronise coroutines
 135  */
 136 typedef struct CoMutex {
 137     bool locked;
 138     CoQueue queue;
 139 } CoMutex;
 140
 141 /**
 142  * Initialises a CoMutex. This must be called before any other operation is used
 143  * on the CoMutex.
 144  */
 145 void qemu_co_mutex_init(CoMutex *mutex);
 146
 147 /**
 148  * Locks the mutex. If the lock cannot be taken immediately, control is
 149  * transferred to the caller of the current coroutine.
 150  */
 151 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
 152
 153 /**
 154  * Unlocks the mutex and schedules the next coroutine that was waiting for this
 155  * lock to be run.
 156  */
 157 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
 158
 159 #endif /* QEMU_COROUTINE_H */