monitor: introduce qmp_dispatcher_co_wake

This makes it possible to turn qmp_dispatcher_co_busy into a static
variable.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 29 insertions, 3 deletions

diff --git a/monitor/qmp.c b/monitor/qmp.c
index dfc2156328..613b74ec74 100644
--- a/monitor/qmp.c
+++ b/monitor/qmp.c
@@ -33,6 +33,27 @@
 #include "qapi/qmp/qlist.h"
 #include "trace.h"
 
+/*
+ * qmp_dispatcher_co_busy is used for synchronisation between the
+ * monitor thread and the main thread to ensure that the dispatcher
+ * coroutine never gets scheduled a second time when it's already
+ * scheduled (scheduling the same coroutine twice is forbidden).
+ *
+ * It is true if the coroutine is active and processing requests.
+ * Additional requests may then be pushed onto mon->qmp_requests,
+ * and @qmp_dispatcher_co_shutdown may be set without further ado.
+ * @qmp_dispatcher_co_busy must not be woken up in this case.
+ *
+ * If false, you also have to set @qmp_dispatcher_co_busy to true and
+ * wake up @qmp_dispatcher_co after pushing the new requests.
+ *
+ * The coroutine will automatically change this variable back to false
+ * before it yields.  Nobody else may set the variable to false.
+ *
+ * Access must be atomic for thread safety.
+ */
+static bool qmp_dispatcher_co_busy = true;
+
 struct QMPRequest {
     /* Owner of the request */
     MonitorQMP *mon;
@@ -334,6 +355,13 @@ void coroutine_fn monitor_qmp_dispatcher_co(void *data)
     qatomic_set(&qmp_dispatcher_co, NULL);
 }
 
+void qmp_dispatcher_co_wake(void)
+{
+    if (!qatomic_xchg(&qmp_dispatcher_co_busy, true)) {
+        aio_co_wake(qmp_dispatcher_co);
+    }
+}
+
 static void handle_qmp_command(void *opaque, QObject *req, Error *err)
 {
     MonitorQMP *mon = opaque;
@@ -395,9 +423,7 @@ static void handle_qmp_command(void *opaque, QObject *req, Error *err)
     }
 
     /* Kick the dispatcher routine */
-    if (!qatomic_xchg(&qmp_dispatcher_co_busy, true)) {
-        aio_co_wake(qmp_dispatcher_co);
-    }
+    qmp_dispatcher_co_wake();
 }
 
 static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)