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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/typedefs.h"
#include "qemu/queue.h"
#include "qemu/timer.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 coroutine_fn qemu_co_queue_next(CoQueue *queue);
/**
* Restarts all coroutines in the CoQueue and leaves the queue empty.
*/
void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
/**
* Enter the next coroutine in the queue
*/
bool qemu_co_enter_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);
typedef struct CoRwlock {
bool writer;
int reader;
CoQueue queue;
} CoRwlock;
/**
* Initialises a CoRwlock. This must be called before any other operation
* is used on the CoRwlock
*/
void qemu_co_rwlock_init(CoRwlock *lock);
/**
* Read locks the CoRwlock. If the lock cannot be taken immediately because
* of a parallel writer, control is transferred to the caller of the current
* coroutine.
*/
void qemu_co_rwlock_rdlock(CoRwlock *lock);
/**
* Write Locks the mutex. If the lock cannot be taken immediately because
* of a parallel reader, control is transferred to the caller of the current
* coroutine.
*/
void qemu_co_rwlock_wrlock(CoRwlock *lock);
/**
* Unlocks the read/write lock and schedules the next coroutine that was
* waiting for this lock to be run.
*/
void qemu_co_rwlock_unlock(CoRwlock *lock);
/**
* Yield the coroutine for a given duration
*
* Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be
* resumed when using aio_poll().
*/
void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type,
int64_t ns);
/**
* Yield until a file descriptor becomes readable
*
* Note that this function clobbers the handlers for the file descriptor.
*/
void coroutine_fn yield_until_fd_readable(int fd);
/**
* Add or subtract from the coroutine pool size
*
* The coroutine implementation keeps a pool of coroutines to be reused by
* qemu_coroutine_create(). This makes coroutine creation cheap. Heavy
* coroutine users should call this to reserve pool space. Call it again with
* a negative number to release pool space.
*/
void qemu_coroutine_adjust_pool_size(int n);
#endif /* QEMU_COROUTINE_H */
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