include/qemu/coroutine-core.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_CORE_H
  16 #define QEMU_COROUTINE_CORE_H
  17
  18 /**
  19  * Coroutines are a mechanism for stack switching and can be used for
  20  * cooperative userspace threading.  These functions provide a simple but
  21  * useful flavor of coroutines that is suitable for writing sequential code,
  22  * rather than callbacks, for operations that need to give up control while
  23  * waiting for events to complete.
  24  *
  25  * These functions are re-entrant and may be used outside the global mutex.
  26  *
  27  * Functions that execute in coroutine context cannot be called
  28  * directly from normal functions.  Use @coroutine_fn to mark such
  29  * functions.  For example:
  30  *
  31  *   static void coroutine_fn foo(void) {
  32  *       ....
  33  *   }
  34  *
  35  * In the future it would be nice to have the compiler or a static
  36  * checker catch misuse of such functions.  This annotation might make
  37  * it possible and in the meantime it serves as documentation.
  38  */
  39
  40 /**
  41  * Mark a function that executes in coroutine context
  42  *
  43  *
  44  * Functions that execute in coroutine context cannot be called
  45  * directly from normal functions.  Use @coroutine_fn to mark such
  46  * functions.  For example:
  47  *
  48  *   static void coroutine_fn foo(void) {
  49  *       ....
  50  *   }
  51  *
  52  * In the future it would be nice to have the compiler or a static
  53  * checker catch misuse of such functions.  This annotation might make
  54  * it possible and in the meantime it serves as documentation.
  55  */
  56
  57 typedef struct Coroutine Coroutine;
  58 typedef struct CoMutex CoMutex;
  59
  60 /**
  61  * Coroutine entry point
  62  *
  63  * When the coroutine is entered for the first time, opaque is passed in as an
  64  * argument.
  65  *
  66  * When this function returns, the coroutine is destroyed automatically and
  67  * execution continues in the caller who last entered the coroutine.
  68  */
  69 typedef void coroutine_fn CoroutineEntry(void *opaque);
  70
  71 /**
  72  * Create a new coroutine
  73  *
  74  * Use qemu_coroutine_enter() to actually transfer control to the coroutine.
  75  * The opaque argument is passed as the argument to the entry point.
  76  */
  77 Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque);
  78
  79 /**
  80  * Transfer control to a coroutine
  81  */
  82 void qemu_coroutine_enter(Coroutine *coroutine);
  83
  84 /**
  85  * Transfer control to a coroutine if it's not active (i.e. part of the call
  86  * stack of the running coroutine). Otherwise, do nothing.
  87  */
  88 void qemu_coroutine_enter_if_inactive(Coroutine *co);
  89
  90 /**
  91  * Transfer control to a coroutine and associate it with ctx
  92  */
  93 void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);
  94
  95 /**
  96  * Transfer control back to a coroutine's caller
  97  *
  98  * This function does not return until the coroutine is re-entered using
  99  * qemu_coroutine_enter().
 100  */
 101 void coroutine_fn qemu_coroutine_yield(void);
 102
 103 /**
 104  * Get the AioContext of the given coroutine
 105  */
 106 AioContext *qemu_coroutine_get_aio_context(Coroutine *co);
 107
 108 /**
 109  * Get the currently executing coroutine
 110  */
 111 Coroutine *qemu_coroutine_self(void);
 112
 113 /**
 114  * Return whether or not currently inside a coroutine
 115  *
 116  * This can be used to write functions that work both when in coroutine context
 117  * and when not in coroutine context.  Note that such functions cannot use the
 118  * coroutine_fn annotation since they work outside coroutine context.
 119  */
 120 bool qemu_in_coroutine(void);
 121
 122 /**
 123  * Return true if the coroutine is currently entered
 124  *
 125  * A coroutine is "entered" if it has not yielded from the current
 126  * qemu_coroutine_enter() call used to run it.  This does not mean that the
 127  * coroutine is currently executing code since it may have transferred control
 128  * to another coroutine using qemu_coroutine_enter().
 129  *
 130  * When several coroutines enter each other there may be no way to know which
 131  * ones have already been entered.  In such situations this function can be
 132  * used to avoid recursively entering coroutines.
 133  */
 134 bool qemu_coroutine_entered(Coroutine *co);
 135
 136 /**
 137  * Initialises a CoMutex. This must be called before any other operation is used
 138  * on the CoMutex.
 139  */
 140 void qemu_co_mutex_init(CoMutex *mutex);
 141
 142 /**
 143  * Locks the mutex. If the lock cannot be taken immediately, control is
 144  * transferred to the caller of the current coroutine.
 145  */
 146 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
 147
 148 /**
 149  * Unlocks the mutex and schedules the next coroutine that was waiting for this
 150  * lock to be run.
 151  */
 152 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
 153
 154 #endif