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/*

 * QEMU coroutine implementation

 *

 * Copyright IBM, Corp. 2011

 *

 * Authors:

 *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>

 *  Kevin Wolf         <kwolf@redhat.com>

 *

 * This work is licensed under the terms of the GNU LGPL, version 2 or later.

 * See the COPYING.LIB file in the top-level directory.

 *

 */

#ifndef QEMU_COROUTINE_H

#define QEMU_COROUTINE_H

#include <stdbool.h>

#include "qemu-queue.h"

/**

 * Coroutines are a mechanism for stack switching and can be used for

 * cooperative userspace threading.  These functions provide a simple but

 * useful flavor of coroutines that is suitable for writing sequential code,

 * rather than callbacks, for operations that need to give up control while

 * waiting for events to complete.

 *

 * These functions are re-entrant and may be used outside the global mutex.

 */

/**

 * Mark a function that executes in coroutine context

 *

 * Functions that execute in coroutine context cannot be called directly from

 * normal functions.  In the future it would be nice to enable compiler or

 * static checker support for catching such errors.  This annotation might make

 * it possible and in the meantime it serves as documentation.

 *

 * For example:

 *

 *   static void coroutine_fn foo(void) {

 *       ....

 *   }

 */

#define coroutine_fn

typedef struct Coroutine Coroutine;

/**

 * Coroutine entry point

 *

 * When the coroutine is entered for the first time, opaque is passed in as an

 * argument.

 *

 * When this function returns, the coroutine is destroyed automatically and

 * execution continues in the caller who last entered the coroutine.

 */

typedef void coroutine_fn CoroutineEntry(void *opaque);

/**

 * Create a new coroutine

 *

 * Use qemu_coroutine_enter() to actually transfer control to the coroutine.

 */

Coroutine *qemu_coroutine_create(CoroutineEntry *entry);

/**

 * Transfer control to a coroutine

 *

 * The opaque argument is passed as the argument to the entry point when

 * entering the coroutine for the first time.  It is subsequently ignored.

 */

void qemu_coroutine_enter(Coroutine *coroutine, void *opaque);

/**

 * Transfer control back to a coroutine's caller

 *

 * This function does not return until the coroutine is re-entered using

 * qemu_coroutine_enter().

 */

void coroutine_fn qemu_coroutine_yield(void);

/**

 * Get the currently executing coroutine

 */

Coroutine *coroutine_fn qemu_coroutine_self(void);

/**

 * Return whether or not currently inside a coroutine

 *

 * This can be used to write functions that work both when in coroutine context

 * and when not in coroutine context.  Note that such functions cannot use the

 * coroutine_fn annotation since they work outside coroutine context.

 */

bool qemu_in_coroutine(void);

/**

 * CoQueues are a mechanism to queue coroutines in order to continue executing

 * them later. They provide the fundamental primitives on which coroutine locks

 * are built.

 */

typedef struct CoQueue {

    QTAILQ_HEAD(, Coroutine) entries;

} CoQueue;

/**

 * Initialise a CoQueue. This must be called before any other operation is used

 * on the CoQueue.

 */

void qemu_co_queue_init(CoQueue *queue);

/**

 * Adds the current coroutine to the CoQueue and transfers control to the

 * caller of the coroutine.

 */

void coroutine_fn qemu_co_queue_wait(CoQueue *queue);

/**

 * Restarts the next coroutine in the CoQueue and removes it from the queue.

 *

 * Returns true if a coroutine was restarted, false if the queue is empty.

 */

bool qemu_co_queue_next(CoQueue *queue);

/**

 * Checks if the CoQueue is empty.

 */

bool qemu_co_queue_empty(CoQueue *queue);

/**

 * Provides a mutex that can be used to synchronise coroutines

 */

typedef struct CoMutex {

    bool locked;

    CoQueue queue;

} CoMutex;

/**

 * Initialises a CoMutex. This must be called before any other operation is used

 * on the CoMutex.

 */

void qemu_co_mutex_init(CoMutex *mutex);

/**

 * Locks the mutex. If the lock cannot be taken immediately, control is

 * transferred to the caller of the current coroutine.

 */

void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);

/**

 * Unlocks the mutex and schedules the next coroutine that was waiting for this

 * lock to be run.

 */

void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);

#endif /* QEMU_COROUTINE_H */