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>

monitor/monitor-internal.h

@@ -165,7 +165,6 @@ typedef QTAILQ_HEAD(MonitorList, Monitor) MonitorList;
 extern IOThread *mon_iothread;
 extern Coroutine *qmp_dispatcher_co;
 extern bool qmp_dispatcher_co_shutdown;
-extern bool qmp_dispatcher_co_busy;
 extern QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
 extern QemuMutex monitor_lock;
 extern MonitorList mon_list;
@@ -183,6 +182,7 @@ void monitor_fdsets_cleanup(void);
 void qmp_send_response(MonitorQMP *mon, const QDict *rsp);
 void monitor_data_destroy_qmp(MonitorQMP *mon);
 void coroutine_fn monitor_qmp_dispatcher_co(void *data);
+void qmp_dispatcher_co_wake(void);
 
 int get_monitor_def(Monitor *mon, int64_t *pval, const char *name);
 void handle_hmp_command(MonitorHMP *mon, const char *cmdline);

monitor/monitor.c

@@ -62,27 +62,6 @@ Coroutine *qmp_dispatcher_co;
  */
 bool qmp_dispatcher_co_shutdown;
 
-/*
- * 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.
- */
-bool qmp_dispatcher_co_busy;
-
 /*
  * Protects mon_list, monitor_qapi_event_state, coroutine_mon,
  * monitor_destroyed.
@@ -685,9 +664,7 @@ void monitor_cleanup(void)
     WITH_QEMU_LOCK_GUARD(&monitor_lock) {
         qmp_dispatcher_co_shutdown = true;
     }
-    if (!qatomic_xchg(&qmp_dispatcher_co_busy, true)) {
+    qmp_dispatcher_co_wake();
-        aio_co_wake(qmp_dispatcher_co);
-    }
 
     AIO_WAIT_WHILE_UNLOCKED(NULL,
                    (aio_poll(iohandler_get_aio_context(), false),
@@ -742,7 +719,6 @@ void monitor_init_globals(void)
      * rid of those assumptions.
      */
     qmp_dispatcher_co = qemu_coroutine_create(monitor_qmp_dispatcher_co, NULL);
-    qatomic_mb_set(&qmp_dispatcher_co_busy, true);
     aio_co_schedule(iohandler_get_aio_context(), qmp_dispatcher_co);
 }
 

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)) {
+    qmp_dispatcher_co_wake();
-        aio_co_wake(qmp_dispatcher_co);
-    }
 }
 
 static void monitor_qmp_read(void *opaque, const uint8_t *buf, int size)