Re: [Qemu-devel] [PATCH v8 0/5] Coroutines for better asynchronous programming

[Aneesh Kumar K.V]

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 */