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Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous progr
From: |
Aneesh Kumar K.V |
Subject: |
Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming |
Date: |
Wed, 27 Jul 2011 17:09:20 +0530 |
User-agent: |
Notmuch/0.5-318-g52e4ded (http://notmuchmail.org) Emacs/23.2.1 (x86_64-pc-linux-gnu) |
On Wed, 27 Jul 2011 12:03:57 +0200, Kevin Wolf <address@hidden> wrote:
> Am 27.07.2011 11:45, schrieb Aneesh Kumar K.V:
> > On Tue, 26 Jul 2011 10:21:12 +0100, Stefan Hajnoczi <address@hidden> wrote:
> >> QEMU is event-driven and suffers when blocking operations are performed
> >> because
> >> VM execution may be stopped until the operation completes. Therefore many
> >> operations that could block are performed asynchronously and a callback is
> >> invoked when the operation has completed. This allows QEMU to continue
> >> executing while the operation is pending.
> >>
> >> The downside to callbacks is that they split up code into many smaller
> >> functions, each of which is a single step in a state machine that quickly
> >> becomes complex and hard to understand. Callback functions also result in
> >> lots
> >> of noise as variables are packed and unpacked into temporary structs that
> >> pass
> >> state to the callback function.
> >>
> >> This patch series introduces coroutines as a solution for writing
> >> asynchronous
> >> code while still having a nice sequential control flow. The semantics are
> >> explained in the second patch. The fourth patch adds automated tests.
> >>
> >> A nice feature of coroutines is that it is relatively easy to take
> >> synchronous
> >> code and lift it into a coroutine to make it asynchronous. Work has been
> >> done
> >> to move qcow2 request processing into coroutines and thereby make it
> >> asynchronous (today qcow2 will perform synchronous metadata accesses).
> >> This
> >> qcow2 work is still ongoing and not quite ready for mainline yet.
> >>
> >> v8:
> >> * Bisectability: introduce gthread implementation before ucontext/fibers
> >
> > Can we also get CoMutex and CoQueue patches also merged. I use them in
> > the VirtFS series.
> >
> > http://repo.or.cz/w/qemu/kevin.git/shortlog/refs/heads/coroutine-devel
> > http://repo.or.cz/w/qemu/v9fs.git/commit/318ef0b9b01cd296f8c30d8288139b9bed859892
>
> I introduce these in my block coroutine patches. I posted a RFC last
> week and the first "real" patch series yesterday, so I hope they get
> review and can be merged into master soon.
>
Can you review the patch that add CoRWlock ?
http://article.gmane.org/gmane.comp.emulators.qemu/105402
Message-id:address@hidden
commit 8c787d8b81aca1f4f7be45adb67b9e1a6dde7f1f
Author: Aneesh Kumar K.V <address@hidden>
Date: Tue May 24 22:14:04 2011 +0530
coroutine: Add CoRwlock support
Signed-off-by: Aneesh Kumar K.V <address@hidden>
diff --git a/qemu-coroutine-lock.c b/qemu-coroutine-lock.c
index 5071fb8..5ecaa94 100644
--- a/qemu-coroutine-lock.c
+++ b/qemu-coroutine-lock.c
@@ -115,3 +115,47 @@ void qemu_co_mutex_unlock(CoMutex *mutex)
trace_qemu_co_mutex_unlock_return(mutex, self);
}
+
+void qemu_co_rwlock_init(CoRwlock *lock)
+{
+ memset(lock, 0, sizeof(*lock));
+ qemu_co_queue_init(&lock->queue);
+}
+
+void qemu_co_rwlock_rdlock(CoRwlock *lock)
+{
+ while (lock->writer) {
+ qemu_co_queue_wait(&lock->queue);
+ }
+ lock->reader++;
+}
+
+void qemu_co_rwlock_unlock(CoRwlock *lock)
+{
+ assert(qemu_in_coroutine());
+ if (lock->writer) {
+ lock->writer--;;
+ assert(lock->writer == 0);
+ while (!qemu_co_queue_empty(&lock->queue)) {
+ /*
+ * Wakeup every body. This will include some
+ * writers too.
+ */
+ qemu_co_queue_next(&lock->queue);
+ }
+ } else {
+ lock->reader--;
+ assert(lock->reader >= 0);
+ /* Wakeup only one waiting writer */
+ qemu_co_queue_next(&lock->queue);
+ }
+}
+
+void qemu_co_rwlock_wrlock(CoRwlock *lock)
+{
+ while (lock->writer || lock->reader) {
+ qemu_co_queue_wait(&lock->queue);
+ }
+ lock->writer++;
+ assert(lock->writer == 1);
+}
diff --git a/qemu-coroutine.h b/qemu-coroutine.h
index 71cfa5a..a9735fb 100644
--- a/qemu-coroutine.h
+++ b/qemu-coroutine.h
@@ -17,6 +17,7 @@
#include <stdbool.h>
#include "qemu-queue.h"
+#include "qemu-thread.h"
/**
* Coroutines are a mechanism for stack switching and can be used for
@@ -114,4 +115,15 @@ void qemu_co_mutex_init(CoMutex *mutex);
void qemu_co_mutex_lock(CoMutex *mutex);
void qemu_co_mutex_unlock(CoMutex *mutex);
+typedef struct CoRwlock {
+ bool writer;
+ int reader;
+ CoQueue queue;
+} CoRwlock;
+
+void qemu_co_rwlock_init(CoRwlock *lock);
+void qemu_co_rwlock_rdlock(CoRwlock *lock);
+void qemu_co_rwlock_wrlock(CoRwlock *lock);
+void qemu_co_rwlock_unlock(CoRwlock *lock);
+
#endif /* QEMU_COROUTINE_H */
- [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming, Stefan Hajnoczi, 2011/07/26
- [Qemu-devel] [PATCH v8 1/5] coroutine: add gthread dependency, Stefan Hajnoczi, 2011/07/26
- [Qemu-devel] [PATCH v8 5/5] coroutine: add test-coroutine --benchmark-lifecycle, Stefan Hajnoczi, 2011/07/26
- [Qemu-devel] [PATCH v8 3/5] coroutine: add ucontext and win32 implementations, Stefan Hajnoczi, 2011/07/26
- [Qemu-devel] [PATCH v8 2/5] coroutine: introduce coroutines API, Stefan Hajnoczi, 2011/07/26
- [Qemu-devel] [PATCH v8 4/5] coroutine: add test-coroutine automated tests, Stefan Hajnoczi, 2011/07/26
- Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming, Stefan Hajnoczi, 2011/07/26
- Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming, Aneesh Kumar K.V, 2011/07/27
- Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming, Aneesh Kumar K.V, 2011/07/27
- Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming, Stefan Hajnoczi, 2011/07/29