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  *
   9  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  10  * See the COPYING.LIB file in the top-level directory.
  11  *
  12  */
  13
  14 #ifndef QEMU_COROUTINE_H
  15 #define QEMU_COROUTINE_H
  16
  17 #include <stdbool.h>
  18
  19 /**
  20  * Coroutines are a mechanism for stack switching and can be used for
  21  * cooperative userspace threading.  These functions provide a simple but
  22  * useful flavor of coroutines that is suitable for writing sequential code,
  23  * rather than callbacks, for operations that need to give up control while
  24  * waiting for events to complete.
  25  *
  26  * These functions are re-entrant and may be used outside the global mutex.
  27  */
  28
  29 /**
  30  * Mark a function that executes in coroutine context
  31  *
  32  * Functions that execute in coroutine context cannot be called directly from
  33  * normal functions.  In the future it would be nice to enable compiler or
  34  * static checker support for catching such errors.  This annotation might make
  35  * it possible and in the meantime it serves as documentation.
  36  *
  37  * For example:
  38  *
  39  *   static void coroutine_fn foo(void) {
  40  *       ....
  41  *   }
  42  */
  43 #define coroutine_fn
  44
  45 typedef struct Coroutine Coroutine;
  46
  47 /**
  48  * Coroutine entry point
  49  *
  50  * When the coroutine is entered for the first time, opaque is passed in as an
  51  * argument.
  52  *
  53  * When this function returns, the coroutine is destroyed automatically and
  54  * execution continues in the caller who last entered the coroutine.
  55  */
  56 typedef void coroutine_fn CoroutineEntry(void *opaque);
  57
  58 /**
  59  * Create a new coroutine
  60  *
  61  * Use qemu_coroutine_enter() to actually transfer control to the coroutine.
  62  */
  63 Coroutine *qemu_coroutine_create(CoroutineEntry *entry);
  64
  65 /**
  66  * Transfer control to a coroutine
  67  *
  68  * The opaque argument is passed as the argument to the entry point when
  69  * entering the coroutine for the first time.  It is subsequently ignored.
  70  */
  71 void qemu_coroutine_enter(Coroutine *coroutine, void *opaque);
  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 #endif /* QEMU_COROUTINE_H */