qemu-char: really fix behavior on can_read = 0

I misread the glib manual, g_source_remove does not let you re-attach
the source later.  This behavior (called "blocking" the source in glib)
is present in glib's source code, but private and not available outside
glib; hence, we have to resort to re-creating the source every time.

In fact, g_source_remove and g_source_destroy are the same thing,
except g_source_destroy is O(1) while g_source_remove scans a potentially
very long list of GSources in the current main loop.  Ugh.  Better
use g_source_destroy explicitly, and leave "tags" to those dummies who
cannot track their pointers' lifetimes.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qemu-char.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

Paolo Bonzini <pbonzini@redhat.com> writes:

> I misread the glib manual, g_source_remove does not let you re-attach
> the source later.  This behavior (called "blocking" the source in glib)
> is present in glib's source code, but private and not available outside
> glib; hence, we have to resort to re-creating the source every time.
>
> In fact, g_source_remove and g_source_destroy are the same thing,
> except g_source_destroy is O(1) while g_source_remove scans a potentially
> very long list of GSources in the current main loop.  Ugh.  Better
> use g_source_destroy explicitly, and leave "tags" to those dummies who
> cannot track their pointers' lifetimes.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Tested-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori

> ---
>  qemu-char.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/qemu-char.c b/qemu-char.c
> index dd410ce..eae17fc 100644
> --- a/qemu-char.c
> +++ b/qemu-char.c
> @@ -596,9 +596,11 @@ typedef struct IOWatchPoll
>  {
>      GSource parent;
>  
> +    GIOChannel *channel;
>      GSource *src;
>  
>      IOCanReadHandler *fd_can_read;
> +    GSourceFunc fd_read;
>      void *opaque;
>  } IOWatchPoll;
>  
> @@ -611,15 +613,19 @@ static gboolean io_watch_poll_prepare(GSource *source, gint *timeout_)
>  {
>      IOWatchPoll *iwp = io_watch_poll_from_source(source);
>      bool now_active = iwp->fd_can_read(iwp->opaque) > 0;
> -    bool was_active = g_source_get_context(iwp->src) != NULL;
> +    bool was_active = iwp->src != NULL;
>      if (was_active == now_active) {
>          return FALSE;
>      }
>  
>      if (now_active) {
> +        iwp->src = g_io_create_watch(iwp->channel, G_IO_IN | G_IO_ERR | G_IO_HUP);
> +        g_source_set_callback(iwp->src, iwp->fd_read, iwp->opaque, NULL);
>          g_source_attach(iwp->src, NULL);
>      } else {
> -        g_source_remove(g_source_get_id(iwp->src));
> +        g_source_destroy(iwp->src);
> +        g_source_unref(iwp->src);
> +        iwp->src = NULL;
>      }
>      return FALSE;
>  }
> @@ -638,7 +644,9 @@ static gboolean io_watch_poll_dispatch(GSource *source, GSourceFunc callback,
>  static void io_watch_poll_finalize(GSource *source)
>  {
>      IOWatchPoll *iwp = io_watch_poll_from_source(source);
> +    g_source_destroy(iwp->src);
>      g_source_unref(iwp->src);
> +    iwp->src = NULL;
>  }
>  
>  static GSourceFuncs io_watch_poll_funcs = {
> @@ -659,8 +667,9 @@ static guint io_add_watch_poll(GIOChannel *channel,
>      iwp = (IOWatchPoll *) g_source_new(&io_watch_poll_funcs, sizeof(IOWatchPoll));
>      iwp->fd_can_read = fd_can_read;
>      iwp->opaque = user_data;
> -    iwp->src = g_io_create_watch(channel, G_IO_IN | G_IO_ERR | G_IO_HUP);
> -    g_source_set_callback(iwp->src, (GSourceFunc)fd_read, user_data, NULL);
> +    iwp->channel = channel;
> +    iwp->fd_read = (GSourceFunc) fd_read;
> +    iwp->src = NULL;
>  
>      return g_source_attach(&iwp->parent, NULL);
>  }
> -- 
> 1.8.1.4

Paolo Bonzini <pbonzini@redhat.com> writes:

> I misread the glib manual, g_source_remove does not let you re-attach
> the source later.  This behavior (called "blocking" the source in glib)
> is present in glib's source code, but private and not available outside
> glib;

Hmm, have you filed a bug upstream asking them to make this available
outside of glib? Would be useful to have...

Regards,

hans

Il 08/04/2013 16:08, Hans de Goede ha scritto:
> 
>> I misread the glib manual, g_source_remove does not let you re-attach
>> the source later.  This behavior (called "blocking" the source in glib)
>> is present in glib's source code, but private and not available outside
>> glib;
> 
> Hmm, have you filed a bug upstream asking them to make this available
> outside of glib? Would be useful to have...

No, I never had much success asking for new glib APIs.

Paolo

Applied.  Thanks.

Regards,

Anthony Liguori