Create one IO thread for the monitors, prepared to handle all the
input/output IOs using existing iothread framework.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 monitor.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/monitor.c b/monitor.c
index 9a8482a962..b44e1f6c86 100644
--- a/monitor.c
+++ b/monitor.c
@@ -76,6 +76,7 @@
 #include "qmp-introspect.h"
 #include "sysemu/qtest.h"
 #include "sysemu/cpus.h"
+#include "sysemu/iothread.h"
 #include "qemu/cutils.h"
 #include "qapi/qmp/dispatch.h"
 
@@ -208,6 +209,12 @@ struct Monitor {
     QLIST_ENTRY(Monitor) entry;
 };
 
+struct MonitorGlobal {
+    IOThread *mon_io_thread;
+};
+
+static struct MonitorGlobal mon_global;
+
 /* QMP checker flags */
 #define QMP_ACCEPT_UNKNOWNS 1
 
@@ -4047,12 +4054,29 @@ static void sortcmdlist(void)
     qsort((void *)info_cmds, array_num, elem_size, compare_mon_cmd);
 }
 
+static GMainContext *monitor_io_context_get(void)
+{
+    return iothread_get_g_main_context(mon_global.mon_io_thread);
+}
+
+static void monitor_io_thread_init(void)
+{
+    mon_global.mon_io_thread = iothread_create("monitor_io_thr",
+                                               &error_abort);
+    /*
+     * Gcontext in iothread is using lazy init - the first time we
+     * fetch the context we'll have that initialized.
+     */
+    monitor_io_context_get();
+}
+
 void monitor_init_globals(void)
 {
     monitor_init_qmp_commands();
     monitor_qapi_event_init();
     sortcmdlist();
     qemu_mutex_init(&monitor_lock);
+    monitor_io_thread_init();
 }
 
 /* These functions just adapt the readline interface in a typesafe way.  We
@@ -4126,10 +4150,23 @@ void monitor_init(Chardev *chr, int flags)
     qemu_mutex_unlock(&monitor_lock);
 }
 
+static void monitor_io_thread_destroy(void)
+{
+    iothread_destroy(mon_global.mon_io_thread);
+    mon_global.mon_io_thread = NULL;
+}
+
 void monitor_cleanup(void)
 {
     Monitor *mon, *next;
 
+    /*
+     * We need to explicitly stop the iothread (but not destroy it),
+     * cleanup the monitor resources, then destroy the iothread.  See
+     * again on the glib bug mentioned in 2b316774f6 for a reason.
+     */
+    iothread_stop(mon_global.mon_io_thread);
+
     qemu_mutex_lock(&monitor_lock);
     QLIST_FOREACH_SAFE(mon, &mon_list, entry, next) {
         QLIST_REMOVE(mon, entry);
@@ -4137,6 +4174,8 @@ void monitor_cleanup(void)
         g_free(mon);
     }
     qemu_mutex_unlock(&monitor_lock);
+
+    monitor_io_thread_destroy();
 }
 
 QemuOptsList qemu_mon_opts = {
-- 
2.13.5

On Fri, Sep 29, 2017 at 11:38:31AM +0800, Peter Xu wrote:
> @@ -4126,10 +4150,23 @@ void monitor_init(Chardev *chr, int flags)
>      qemu_mutex_unlock(&monitor_lock);
>  }
>  
> +static void monitor_io_thread_destroy(void)
> +{
> +    iothread_destroy(mon_global.mon_io_thread);
> +    mon_global.mon_io_thread = NULL;
> +}
> +
>  void monitor_cleanup(void)
>  {
>      Monitor *mon, *next;
>  
> +    /*
> +     * We need to explicitly stop the iothread (but not destroy it),
> +     * cleanup the monitor resources, then destroy the iothread.  See
> +     * again on the glib bug mentioned in 2b316774f6 for a reason.
> +     */
> +    iothread_stop(mon_global.mon_io_thread);
> +
>      qemu_mutex_lock(&monitor_lock);
>      QLIST_FOREACH_SAFE(mon, &mon_list, entry, next) {
>          QLIST_REMOVE(mon, entry);
> @@ -4137,6 +4174,8 @@ void monitor_cleanup(void)
>          g_free(mon);
>      }
>      qemu_mutex_unlock(&monitor_lock);
> +
> +    monitor_io_thread_destroy();
>  }

Minor style comment, I would inline monitor_io_thread_destroy() into
monitor_cleanup() instead of making it a function.

monitor_io_thread_destroy() relies on iothread_stop() being called
first.  Defining a function with no doc comment creates a risk that
someone else will call it in the future without first calling
iothread_stop().  It's safer to inline the code where it cannot be
misused by accident.

Also, please name things "iothread" instead of "io_thread" for
consistency.

Stefan

On Thu, Oct 12, 2017 at 01:29:11PM +0100, Stefan Hajnoczi wrote:
> On Fri, Sep 29, 2017 at 11:38:31AM +0800, Peter Xu wrote:
> > @@ -4126,10 +4150,23 @@ void monitor_init(Chardev *chr, int flags)
> >      qemu_mutex_unlock(&monitor_lock);
> >  }
> >  
> > +static void monitor_io_thread_destroy(void)
> > +{
> > +    iothread_destroy(mon_global.mon_io_thread);
> > +    mon_global.mon_io_thread = NULL;
> > +}
> > +
> >  void monitor_cleanup(void)
> >  {
> >      Monitor *mon, *next;
> >  
> > +    /*
> > +     * We need to explicitly stop the iothread (but not destroy it),
> > +     * cleanup the monitor resources, then destroy the iothread.  See
> > +     * again on the glib bug mentioned in 2b316774f6 for a reason.
> > +     */
> > +    iothread_stop(mon_global.mon_io_thread);
> > +
> >      qemu_mutex_lock(&monitor_lock);
> >      QLIST_FOREACH_SAFE(mon, &mon_list, entry, next) {
> >          QLIST_REMOVE(mon, entry);
> > @@ -4137,6 +4174,8 @@ void monitor_cleanup(void)
> >          g_free(mon);
> >      }
> >      qemu_mutex_unlock(&monitor_lock);
> > +
> > +    monitor_io_thread_destroy();
> >  }
> 
> Minor style comment, I would inline monitor_io_thread_destroy() into
> monitor_cleanup() instead of making it a function.
> 
> monitor_io_thread_destroy() relies on iothread_stop() being called
> first.  Defining a function with no doc comment creates a risk that
> someone else will call it in the future without first calling
> iothread_stop().  It's safer to inline the code where it cannot be
> misused by accident.

There will be some more lines added to monitor_io_thread_destroy() in
follow-up patches.  I was trying to put iothread things all into this
function but I cannot really do that since the glib bug (then we'll
need explicit iothread_stop() above). But sure, I can inline them all.

> 
> Also, please name things "iothread" instead of "io_thread" for
> consistency.

Will do.  Thanks,

-- 
Peter Xu

On Mon, Oct 16, 2017 at 03:16:17PM +0800, Peter Xu wrote:
> On Thu, Oct 12, 2017 at 01:29:11PM +0100, Stefan Hajnoczi wrote:
> > On Fri, Sep 29, 2017 at 11:38:31AM +0800, Peter Xu wrote:
> > > @@ -4126,10 +4150,23 @@ void monitor_init(Chardev *chr, int flags)
> > >      qemu_mutex_unlock(&monitor_lock);
> > >  }
> > >  
> > > +static void monitor_io_thread_destroy(void)
> > > +{
> > > +    iothread_destroy(mon_global.mon_io_thread);
> > > +    mon_global.mon_io_thread = NULL;
> > > +}
> > > +
> > >  void monitor_cleanup(void)
> > >  {
> > >      Monitor *mon, *next;
> > >  
> > > +    /*
> > > +     * We need to explicitly stop the iothread (but not destroy it),
> > > +     * cleanup the monitor resources, then destroy the iothread.  See
> > > +     * again on the glib bug mentioned in 2b316774f6 for a reason.
> > > +     */
> > > +    iothread_stop(mon_global.mon_io_thread);
> > > +
> > >      qemu_mutex_lock(&monitor_lock);
> > >      QLIST_FOREACH_SAFE(mon, &mon_list, entry, next) {
> > >          QLIST_REMOVE(mon, entry);
> > > @@ -4137,6 +4174,8 @@ void monitor_cleanup(void)
> > >          g_free(mon);
> > >      }
> > >      qemu_mutex_unlock(&monitor_lock);
> > > +
> > > +    monitor_io_thread_destroy();
> > >  }
> > 
> > Minor style comment, I would inline monitor_io_thread_destroy() into
> > monitor_cleanup() instead of making it a function.
> > 
> > monitor_io_thread_destroy() relies on iothread_stop() being called
> > first.  Defining a function with no doc comment creates a risk that
> > someone else will call it in the future without first calling
> > iothread_stop().  It's safer to inline the code where it cannot be
> > misused by accident.
> 
> There will be some more lines added to monitor_io_thread_destroy() in
> follow-up patches.  I was trying to put iothread things all into this
> function but I cannot really do that since the glib bug (then we'll
> need explicit iothread_stop() above). But sure, I can inline them all.

Or add a doc comment to monitor_io_thread_destroy() so callers know
about the assumption.

Stefan