324 lines
10 KiB
C
324 lines
10 KiB
C
/*
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* QEMU coroutine implementation
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*
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* Copyright IBM, Corp. 2011
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*
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* Authors:
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* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
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* Kevin Wolf <kwolf@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef QEMU_COROUTINE_H
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#define QEMU_COROUTINE_H
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#include "qemu/queue.h"
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#include "qemu/timer.h"
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/**
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* Coroutines are a mechanism for stack switching and can be used for
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* cooperative userspace threading. These functions provide a simple but
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* useful flavor of coroutines that is suitable for writing sequential code,
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* rather than callbacks, for operations that need to give up control while
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* waiting for events to complete.
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*
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* These functions are re-entrant and may be used outside the global mutex.
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*/
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/**
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* Mark a function that executes in coroutine context
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*
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* Functions that execute in coroutine context cannot be called directly from
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* normal functions. In the future it would be nice to enable compiler or
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* static checker support for catching such errors. This annotation might make
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* it possible and in the meantime it serves as documentation.
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*
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* For example:
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*
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* static void coroutine_fn foo(void) {
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* ....
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* }
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*/
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#define coroutine_fn
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typedef struct Coroutine Coroutine;
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/**
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* Coroutine entry point
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*
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* When the coroutine is entered for the first time, opaque is passed in as an
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* argument.
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*
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* When this function returns, the coroutine is destroyed automatically and
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* execution continues in the caller who last entered the coroutine.
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*/
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typedef void coroutine_fn CoroutineEntry(void *opaque);
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/**
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* Create a new coroutine
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*
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* Use qemu_coroutine_enter() to actually transfer control to the coroutine.
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* The opaque argument is passed as the argument to the entry point.
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*/
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Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque);
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/**
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* Transfer control to a coroutine
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*/
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void qemu_coroutine_enter(Coroutine *coroutine);
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/**
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* Transfer control to a coroutine if it's not active (i.e. part of the call
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* stack of the running coroutine). Otherwise, do nothing.
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*/
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void qemu_coroutine_enter_if_inactive(Coroutine *co);
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/**
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* Transfer control to a coroutine and associate it with ctx
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*/
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void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);
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/**
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* Transfer control back to a coroutine's caller
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*
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* This function does not return until the coroutine is re-entered using
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* qemu_coroutine_enter().
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*/
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void coroutine_fn qemu_coroutine_yield(void);
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/**
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* Get the AioContext of the given coroutine
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*/
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AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);
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/**
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* Get the currently executing coroutine
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*/
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Coroutine *coroutine_fn qemu_coroutine_self(void);
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/**
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* Return whether or not currently inside a coroutine
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*
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* This can be used to write functions that work both when in coroutine context
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* and when not in coroutine context. Note that such functions cannot use the
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* coroutine_fn annotation since they work outside coroutine context.
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*/
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bool qemu_in_coroutine(void);
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/**
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* Return true if the coroutine is currently entered
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*
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* A coroutine is "entered" if it has not yielded from the current
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* qemu_coroutine_enter() call used to run it. This does not mean that the
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* coroutine is currently executing code since it may have transferred control
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* to another coroutine using qemu_coroutine_enter().
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*
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* When several coroutines enter each other there may be no way to know which
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* ones have already been entered. In such situations this function can be
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* used to avoid recursively entering coroutines.
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*/
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bool qemu_coroutine_entered(Coroutine *co);
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/**
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* Provides a mutex that can be used to synchronise coroutines
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*/
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struct CoWaitRecord;
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struct CoMutex {
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/* Count of pending lockers; 0 for a free mutex, 1 for an
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* uncontended mutex.
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*/
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unsigned locked;
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/* Context that is holding the lock. Useful to avoid spinning
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* when two coroutines on the same AioContext try to get the lock. :)
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*/
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AioContext *ctx;
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/* A queue of waiters. Elements are added atomically in front of
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* from_push. to_pop is only populated, and popped from, by whoever
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* is in charge of the next wakeup. This can be an unlocker or,
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* through the handoff protocol, a locker that is about to go to sleep.
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*/
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QSLIST_HEAD(, CoWaitRecord) from_push, to_pop;
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unsigned handoff, sequence;
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Coroutine *holder;
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};
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/**
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* Initialises a CoMutex. This must be called before any other operation is used
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* on the CoMutex.
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*/
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void qemu_co_mutex_init(CoMutex *mutex);
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/**
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* Locks the mutex. If the lock cannot be taken immediately, control is
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* transferred to the caller of the current coroutine.
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*/
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void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
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/**
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* Unlocks the mutex and schedules the next coroutine that was waiting for this
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* lock to be run.
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*/
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void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
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/**
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* Assert that the current coroutine holds @mutex.
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*/
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static inline coroutine_fn void qemu_co_mutex_assert_locked(CoMutex *mutex)
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{
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/*
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* mutex->holder doesn't need any synchronisation if the assertion holds
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* true because the mutex protects it. If it doesn't hold true, we still
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* don't mind if another thread takes or releases mutex behind our back,
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* because the condition will be false no matter whether we read NULL or
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* the pointer for any other coroutine.
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*/
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assert(atomic_read(&mutex->locked) &&
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mutex->holder == qemu_coroutine_self());
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}
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/**
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* CoQueues are a mechanism to queue coroutines in order to continue executing
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* them later. They are similar to condition variables, but they need help
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* from an external mutex in order to maintain thread-safety.
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*/
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typedef struct CoQueue {
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QSIMPLEQ_HEAD(, Coroutine) entries;
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} CoQueue;
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/**
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* Initialise a CoQueue. This must be called before any other operation is used
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* on the CoQueue.
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*/
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void qemu_co_queue_init(CoQueue *queue);
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/**
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* Adds the current coroutine to the CoQueue and transfers control to the
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* caller of the coroutine. The mutex is unlocked during the wait and
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* locked again afterwards.
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*/
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#define qemu_co_queue_wait(queue, lock) \
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qemu_co_queue_wait_impl(queue, QEMU_MAKE_LOCKABLE(lock))
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void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock);
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/**
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* Removes the next coroutine from the CoQueue, and wake it up.
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* Returns true if a coroutine was removed, false if the queue is empty.
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*/
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bool coroutine_fn qemu_co_queue_next(CoQueue *queue);
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/**
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* Empties the CoQueue; all coroutines are woken up.
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*/
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void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
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/**
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* Removes the next coroutine from the CoQueue, and wake it up. Unlike
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* qemu_co_queue_next, this function releases the lock during aio_co_wake
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* because it is meant to be used outside coroutine context; in that case, the
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* coroutine is entered immediately, before qemu_co_enter_next returns.
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*
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* If used in coroutine context, qemu_co_enter_next is equivalent to
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* qemu_co_queue_next.
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*/
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#define qemu_co_enter_next(queue, lock) \
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qemu_co_enter_next_impl(queue, QEMU_MAKE_LOCKABLE(lock))
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bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock);
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/**
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* Checks if the CoQueue is empty.
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*/
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bool qemu_co_queue_empty(CoQueue *queue);
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typedef struct CoRwlock {
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int pending_writer;
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int reader;
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CoMutex mutex;
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CoQueue queue;
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} CoRwlock;
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/**
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* Initialises a CoRwlock. This must be called before any other operation
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* is used on the CoRwlock
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*/
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void qemu_co_rwlock_init(CoRwlock *lock);
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/**
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* Read locks the CoRwlock. If the lock cannot be taken immediately because
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* of a parallel writer, control is transferred to the caller of the current
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* coroutine.
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*/
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void qemu_co_rwlock_rdlock(CoRwlock *lock);
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/**
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* Write Locks the CoRwlock from a reader. This is a bit more efficient than
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* @qemu_co_rwlock_unlock followed by a separate @qemu_co_rwlock_wrlock.
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* However, if the lock cannot be upgraded immediately, control is transferred
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* to the caller of the current coroutine. Also, @qemu_co_rwlock_upgrade
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* only overrides CoRwlock fairness if there are no concurrent readers, so
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* another writer might run while @qemu_co_rwlock_upgrade blocks.
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*/
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void qemu_co_rwlock_upgrade(CoRwlock *lock);
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/**
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* Downgrades a write-side critical section to a reader. Downgrading with
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* @qemu_co_rwlock_downgrade never blocks, unlike @qemu_co_rwlock_unlock
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* followed by @qemu_co_rwlock_rdlock. This makes it more efficient, but
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* may also sometimes be necessary for correctness.
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*/
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void qemu_co_rwlock_downgrade(CoRwlock *lock);
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/**
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* Write Locks the mutex. If the lock cannot be taken immediately because
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* of a parallel reader, control is transferred to the caller of the current
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* coroutine.
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*/
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void qemu_co_rwlock_wrlock(CoRwlock *lock);
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/**
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* Unlocks the read/write lock and schedules the next coroutine that was
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* waiting for this lock to be run.
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*/
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void qemu_co_rwlock_unlock(CoRwlock *lock);
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typedef struct QemuCoSleepState QemuCoSleepState;
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/**
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* Yield the coroutine for a given duration. During this yield, @sleep_state
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* (if not NULL) is set to an opaque pointer, which may be used for
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* qemu_co_sleep_wake(). Be careful, the pointer is set back to zero when the
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* timer fires. Don't save the obtained value to other variables and don't call
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* qemu_co_sleep_wake from another aio context.
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*/
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void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
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QemuCoSleepState **sleep_state);
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static inline void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
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{
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qemu_co_sleep_ns_wakeable(type, ns, NULL);
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}
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/**
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* Wake a coroutine if it is sleeping in qemu_co_sleep_ns. The timer will be
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* deleted. @sleep_state must be the variable whose address was given to
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* qemu_co_sleep_ns() and should be checked to be non-NULL before calling
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* qemu_co_sleep_wake().
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*/
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void qemu_co_sleep_wake(QemuCoSleepState *sleep_state);
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/**
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* Yield until a file descriptor becomes readable
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*
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* Note that this function clobbers the handlers for the file descriptor.
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*/
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void coroutine_fn yield_until_fd_readable(int fd);
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#include "qemu/lockable.h"
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#endif /* QEMU_COROUTINE_H */
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