/*
* 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 "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.
* The opaque argument is passed as the argument to the entry point.
*/
Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque);
/**
* Transfer control to a coroutine
*/
void qemu_coroutine_enter(Coroutine *coroutine);
/**
* Transfer control to a coroutine if it's not active (i.e. part of the call
* stack of the running coroutine). Otherwise, do nothing.
*/
void qemu_coroutine_enter_if_inactive(Coroutine *co);
/**
* Transfer control to a coroutine and associate it with ctx
*/
void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);
/**
* 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 AioContext of the given coroutine
*/
AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);
/**
* 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);
/**
* Return true if the coroutine is currently entered
*
* A coroutine is "entered" if it has not yielded from the current
* qemu_coroutine_enter() call used to run it. This does not mean that the
* coroutine is currently executing code since it may have transferred control
* to another coroutine using qemu_coroutine_enter().
*
* When several coroutines enter each other there may be no way to know which
* ones have already been entered. In such situations this function can be
* used to avoid recursively entering coroutines.
*/
bool qemu_coroutine_entered(Coroutine *co);
/**
* Provides a mutex that can be used to synchronise coroutines
*/
struct CoWaitRecord;
struct CoMutex {
/* Count of pending lockers; 0 for a free mutex, 1 for an
* uncontended mutex.
*/
unsigned locked;
/* Context that is holding the lock. Useful to avoid spinning
* when two coroutines on the same AioContext try to get the lock. :)
*/
AioContext *ctx;
/* A queue of waiters. Elements are added atomically in front of
* from_push. to_pop is only populated, and popped from, by whoever
* is in charge of the next wakeup. This can be an unlocker or,
* through the handoff protocol, a locker that is about to go to sleep.
*/
QSLIST_HEAD(, CoWaitRecord) from_push, to_pop;
unsigned handoff, sequence;
Coroutine *holder;
};
/**
* 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);
/**
* Assert that the current coroutine holds @mutex.
*/
static inline coroutine_fn void qemu_co_mutex_assert_locked(CoMutex *mutex)
{
/*
* mutex->holder doesn't need any synchronisation if the assertion holds
* true because the mutex protects it. If it doesn't hold true, we still
* don't mind if another thread takes or releases mutex behind our back,
* because the condition will be false no matter whether we read NULL or
* the pointer for any other coroutine.
*/
assert(qatomic_read(&mutex->locked) &&
mutex->holder == qemu_coroutine_self());
}
/**
* CoQueues are a mechanism to queue coroutines in order to continue executing
* them later. They are similar to condition variables, but they need help
* from an external mutex in order to maintain thread-safety.
*/
typedef struct CoQueue {
QSIMPLEQ_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. The mutex is unlocked during the wait and
* locked again afterwards.
*/
#define qemu_co_queue_wait(queue, lock) \
qemu_co_queue_wait_impl(queue, QEMU_MAKE_LOCKABLE(lock))
void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock);
/**
* Removes the next coroutine from the CoQueue, and wake it up.
* Returns true if a coroutine was removed, false if the queue is empty.
*/
bool coroutine_fn qemu_co_queue_next(CoQueue *queue);
/**
* Empties the CoQueue; all coroutines are woken up.
*/
void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
/**
* Removes the next coroutine from the CoQueue, and wake it up. Unlike
* qemu_co_queue_next, this function releases the lock during aio_co_wake
* because it is meant to be used outside coroutine context; in that case, the
* coroutine is entered immediately, before qemu_co_enter_next returns.
*
* If used in coroutine context, qemu_co_enter_next is equivalent to
* qemu_co_queue_next.
*/
#define qemu_co_enter_next(queue, lock) \
qemu_co_enter_next_impl(queue, QEMU_MAKE_LOCKABLE(lock))
bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock);
/**
* Checks if the CoQueue is empty.
*/
bool qemu_co_queue_empty(CoQueue *queue);
typedef struct CoRwlock {
int pending_writer;
int reader;
CoMutex mutex;
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 CoRwlock from a reader. This is a bit more efficient than
* @qemu_co_rwlock_unlock followed by a separate @qemu_co_rwlock_wrlock.
* However, if the lock cannot be upgraded immediately, control is transferred
* to the caller of the current coroutine. Also, @qemu_co_rwlock_upgrade
* only overrides CoRwlock fairness if there are no concurrent readers, so
* another writer might run while @qemu_co_rwlock_upgrade blocks.
*/
void qemu_co_rwlock_upgrade(CoRwlock *lock);
/**
* Downgrades a write-side critical section to a reader. Downgrading with
* @qemu_co_rwlock_downgrade never blocks, unlike @qemu_co_rwlock_unlock
* followed by @qemu_co_rwlock_rdlock. This makes it more efficient, but
* may also sometimes be necessary for correctness.
*/
void qemu_co_rwlock_downgrade(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);
typedef struct QemuCoSleepState QemuCoSleepState;
/**
* Yield the coroutine for a given duration. During this yield, @sleep_state
* (if not NULL) is set to an opaque pointer, which may be used for
* qemu_co_sleep_wake(). Be careful, the pointer is set back to zero when the
* timer fires. Don't save the obtained value to other variables and don't call
* qemu_co_sleep_wake from another aio context.
*/
void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
QemuCoSleepState **sleep_state);
static inline void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
{
qemu_co_sleep_ns_wakeable(type, ns, NULL);
}
/**
* Wake a coroutine if it is sleeping in qemu_co_sleep_ns. The timer will be
* deleted. @sleep_state must be the variable whose address was given to
* qemu_co_sleep_ns() and should be checked to be non-NULL before calling
* qemu_co_sleep_wake().
*/
void qemu_co_sleep_wake(QemuCoSleepState *sleep_state);
/**
* 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);
#include "qemu/lockable.h"
#endif /* QEMU_COROUTINE_H */
