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qemu/qemu-coroutine.c

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coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
/*
* QEMU coroutines
*
* 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.
*
*/
#include "trace.h"
#include "qemu-common.h"
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
#include "qemu/thread.h"
block: move include files to include/block/ Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2012-12-18 01:19:44 +08:00
#include "block/coroutine.h"
#include "block/coroutine_int.h"
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
enum {
/* Maximum free pool size prevents holding too many freed coroutines */
POOL_MAX_SIZE = 64,
};
/** Free list to speed up creation */
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
static QemuMutex pool_lock;
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);
static unsigned int pool_size;
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
{
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
Coroutine *co;
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
qemu_mutex_lock(&pool_lock);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
co = QSLIST_FIRST(&pool);
if (co) {
QSLIST_REMOVE_HEAD(&pool, pool_next);
pool_size--;
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
}
qemu_mutex_unlock(&pool_lock);
if (!co) {
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
co = qemu_coroutine_new();
}
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
co->entry = entry;
coroutine: stop using AioContext in CoQueue qemu_co_queue_next(&queue) arranges that the next queued coroutine is run at a later point in time. This deferred restart is useful because the caller may not want to transfer control yet. This behavior was implemented using QEMUBH in the past, which meant that CoQueue (and hence CoMutex and CoRwlock) had a dependency on the AioContext event loop. This hidden dependency causes trouble when we move to a world with multiple event loops - now qemu_co_queue_next() needs to know which event loop to schedule the QEMUBH in. After pondering how to stash AioContext I realized the best solution is to not use AioContext at all. This patch implements the deferred restart behavior purely in terms of coroutines and no longer uses QEMUBH. Here is how it works: Each Coroutine has a wakeup queue that starts out empty. When qemu_co_queue_next() is called, the next coroutine is added to our wakeup queue. The wakeup queue is processed when we yield or terminate. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:26 +08:00
QTAILQ_INIT(&co->co_queue_wakeup);
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
return co;
}
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
static void coroutine_delete(Coroutine *co)
{
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
qemu_mutex_lock(&pool_lock);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
if (pool_size < POOL_MAX_SIZE) {
QSLIST_INSERT_HEAD(&pool, co, pool_next);
co->caller = NULL;
pool_size++;
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
qemu_mutex_unlock(&pool_lock);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
return;
}
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
qemu_mutex_unlock(&pool_lock);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
qemu_coroutine_delete(co);
}
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
static void __attribute__((constructor)) coroutine_pool_init(void)
{
qemu_mutex_init(&pool_lock);
}
static void __attribute__((destructor)) coroutine_pool_cleanup(void)
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
{
Coroutine *co;
Coroutine *tmp;
QSLIST_FOREACH_SAFE(co, &pool, pool_next, tmp) {
QSLIST_REMOVE_HEAD(&pool, pool_next);
qemu_coroutine_delete(co);
}
coroutine: protect global pool with a mutex The coroutine freelist is a global pool of unused coroutines. It avoids the setup/teardown overhead associated with the coroutine lifecycle. Since the pool is global, we need to synchronize access so that coroutines can be used outside the BQL. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:25 +08:00
qemu_mutex_destroy(&pool_lock);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
}
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
static void coroutine_swap(Coroutine *from, Coroutine *to)
{
CoroutineAction ret;
ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD);
coroutine: stop using AioContext in CoQueue qemu_co_queue_next(&queue) arranges that the next queued coroutine is run at a later point in time. This deferred restart is useful because the caller may not want to transfer control yet. This behavior was implemented using QEMUBH in the past, which meant that CoQueue (and hence CoMutex and CoRwlock) had a dependency on the AioContext event loop. This hidden dependency causes trouble when we move to a world with multiple event loops - now qemu_co_queue_next() needs to know which event loop to schedule the QEMUBH in. After pondering how to stash AioContext I realized the best solution is to not use AioContext at all. This patch implements the deferred restart behavior purely in terms of coroutines and no longer uses QEMUBH. Here is how it works: Each Coroutine has a wakeup queue that starts out empty. When qemu_co_queue_next() is called, the next coroutine is added to our wakeup queue. The wakeup queue is processed when we yield or terminate. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2013-05-17 21:51:26 +08:00
qemu_co_queue_run_restart(to);
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
switch (ret) {
case COROUTINE_YIELD:
return;
case COROUTINE_TERMINATE:
trace_qemu_coroutine_terminate(to);
coroutine: move pooling to common code The coroutine pool code is duplicated between the ucontext and sigaltstack backends, and absent from the win32 backend. But the code can be shared easily by moving it to qemu-coroutine.c. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2013-02-19 18:59:09 +08:00
coroutine_delete(to);
coroutine: introduce coroutines Asynchronous code is becoming very complex. At the same time synchronous code is growing because it is convenient to write. Sometimes duplicate code paths are even added, one synchronous and the other asynchronous. This patch introduces coroutines which allow code that looks synchronous but is asynchronous under the covers. A coroutine has its own stack and is therefore able to preserve state across blocking operations, which traditionally require callback functions and manual marshalling of parameters. Creating and starting a coroutine is easy: coroutine = qemu_coroutine_create(my_coroutine); qemu_coroutine_enter(coroutine, my_data); The coroutine then executes until it returns or yields: void coroutine_fn my_coroutine(void *opaque) { MyData *my_data = opaque; /* do some work */ qemu_coroutine_yield(); /* do some more work */ } Yielding switches control back to the caller of qemu_coroutine_enter(). This is typically used to switch back to the main thread's event loop after issuing an asynchronous I/O request. The request callback will then invoke qemu_coroutine_enter() once more to switch back to the coroutine. Note that if coroutines are used only from threads which hold the global mutex they will never execute concurrently. This makes programming with coroutines easier than with threads. Race conditions cannot occur since only one coroutine may be active at any time. Other coroutines can only run across yield. This coroutines implementation is based on the gtk-vnc implementation written by Anthony Liguori <anthony@codemonkey.ws> but it has been significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use setjmp()/longjmp() instead of the more expensive swapcontext() and by Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
2011-01-18 00:08:14 +08:00
return;
default:
abort();
}
}
void qemu_coroutine_enter(Coroutine *co, void *opaque)
{
Coroutine *self = qemu_coroutine_self();
trace_qemu_coroutine_enter(self, co, opaque);
if (co->caller) {
fprintf(stderr, "Co-routine re-entered recursively\n");
abort();
}
co->caller = self;
co->entry_arg = opaque;
coroutine_swap(self, co);
}
void coroutine_fn qemu_coroutine_yield(void)
{
Coroutine *self = qemu_coroutine_self();
Coroutine *to = self->caller;
trace_qemu_coroutine_yield(self, to);
if (!to) {
fprintf(stderr, "Co-routine is yielding to no one\n");
abort();
}
self->caller = NULL;
coroutine_swap(self, to);
}