Re: [Qemu-devel] [PATCH] char: kick main loop after adding a watch

["Richard W.M. Jones" <rjones@redhat.com>]

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On Fri, Mar 31, 2017 at 06:53:56PM +0200, Paolo Bonzini wrote:
> glib is expecting QEMU to use g_main_context_acquire around accesses to 
> GMainContext.  However QEMU is not doing that, instead it is taking its 
> own mutex.  So we should add g_main_context_acquire and
> g_main_context_release in the two implementations of 
> os_host_main_loop_wait; these should undo the effect of Frediano's 
> glib patch.

Based on this paragraph, I'm testing the attached patch, and it does
also appear to solve the hanging serial port problem.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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>From d46afa25dae0f1d057cfac3a0b6ae94771be51f2 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Fri, 31 Mar 2017 18:29:01 +0100
Subject: [PATCH] main-loop: Acquire main_context lock around
 os_host_main_loop_wait.

---
 util/main-loop.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/util/main-loop.c b/util/main-loop.c
index 4534c89..19cad6b 100644
--- a/util/main-loop.c
+++ b/util/main-loop.c
@@ -218,9 +218,12 @@ static void glib_pollfds_poll(void)
 
 static int os_host_main_loop_wait(int64_t timeout)
 {
+    GMainContext *context = g_main_context_default();
     int ret;
     static int spin_counter;
 
+    g_main_context_acquire(context);
+
     glib_pollfds_fill(&timeout);
 
     /* If the I/O thread is very busy or we are incorrectly busy waiting in
@@ -256,6 +259,9 @@ static int os_host_main_loop_wait(int64_t timeout)
     }
 
     glib_pollfds_poll();
+
+    g_main_context_release(context);
+
     return ret;
 }
 #else
@@ -412,12 +418,15 @@ static int os_host_main_loop_wait(int64_t timeout)
     fd_set rfds, wfds, xfds;
     int nfds;
 
+    g_main_context_acquire(context);
+
     /* XXX: need to suppress polling by better using win32 events */
     ret = 0;
     for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
         ret |= pe->func(pe->opaque);
     }
     if (ret != 0) {
+        g_main_context_release(context);
         return ret;
     }
 
@@ -472,6 +481,8 @@ static int os_host_main_loop_wait(int64_t timeout)
         g_main_context_dispatch(context);
     }
 
+    g_main_context_release(context);
+
     return select_ret || g_poll_ret;
 }
 #endif
-- 
2.9.3