/* * 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); 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); #endif /* QEMU_COROUTINE_H */