[PATCH xserver] dix: Allow secondary threads to use the work queue

[Peter Hutterer]

On Thu, Feb 23, 2017 at 04:25:35PM -0500, Adam Jackson wrote:
> The work queue code is reentrant with itself on a single thread, but not
> when the queue is modified from thread A while being run on thread B.
> We will only ever run it from the main thread, but the input thread
> wants to be able to queue work for event emission. Mutex the list so it
> can do so safely.
> 
> This does mean queued work should be cheap to execute since if the lock
> is contended the input thread will block. That was always true though.
> If this contention turns out to be a problem, we can fix how we walk the
> work queue to hold the lock less.
> 
> Signed-off-by: Adam Jackson <ajax at redhat.com>
> ---
>  dix/dixutils.c | 22 ++++++++++++++++++++++
>  dix/main.c     |  2 ++
>  include/dix.h  |  3 +--
>  3 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/dix/dixutils.c b/dix/dixutils.c
> index 540023c..a282b15 100644
> --- a/dix/dixutils.c
> +++ b/dix/dixutils.c
> @@ -506,12 +506,29 @@ InitBlockAndWakeupHandlers(void)
>  
>  WorkQueuePtr workQueue;
>  static WorkQueuePtr *workQueueLast = &workQueue;
> +static pthread_mutex_t wq_mutex;

I'm not a fan of changing the naming scheme here...

otherwise Reviewed-by: Peter Hutterer <peter.hutterer at who-t.net>

Cheers,
   Peter

> +
> +Bool
> +InitWorkQueue(void)
> +{
> +    if (serverGeneration == 1) {
> +        pthread_mutexattr_t attr;
> +
> +        pthread_mutexattr_init(&attr);
> +        pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
> +        if (pthread_mutex_init(&wq_mutex, &attr))
> +            FatalError("Could not initialize work queue lock");
> +    }
> +
> +    return TRUE;
> +}
>  
>  void
>  ProcessWorkQueue(void)
>  {
>      WorkQueuePtr q, *p;
>  
> +    pthread_mutex_lock(&wq_mutex);
>      p = &workQueue;
>      /*
>       * Scan the work queue once, calling each function.  Those
> @@ -530,6 +547,7 @@ ProcessWorkQueue(void)
>          }
>      }
>      workQueueLast = p;
> +    pthread_mutex_unlock(&wq_mutex);
>  }
>  
>  void
> @@ -537,6 +555,7 @@ ProcessWorkQueueZombies(void)
>  {
>      WorkQueuePtr q, *p;
>  
> +    pthread_mutex_lock(&wq_mutex);
>      p = &workQueue;
>      while ((q = *p)) {
>          if (q->client && q->client->clientGone) {
> @@ -550,6 +569,7 @@ ProcessWorkQueueZombies(void)
>          }
>      }
>      workQueueLast = p;
> +    pthread_mutex_unlock(&wq_mutex);
>  }
>  
>  Bool
> @@ -565,8 +585,10 @@ QueueWorkProc(Bool (*function) (ClientPtr pClient, void *closure),
>      q->client = client;
>      q->closure = closure;
>      q->next = NULL;
> +    pthread_mutex_lock(&wq_mutex);
>      *workQueueLast = q;
>      workQueueLast = &q->next;
> +    pthread_mutex_unlock(&wq_mutex);
>      return TRUE;
>  }
>  
> diff --git a/dix/main.c b/dix/main.c
> index 4947062..0278bf5 100644
> --- a/dix/main.c
> +++ b/dix/main.c
> @@ -154,6 +154,8 @@ dix_main(int argc, char *argv[], char *envp[])
>          DPMSPowerLevel = 0;
>  #endif
>          InitBlockAndWakeupHandlers();
> +        InitWorkQueue();
> +
>          /* Perform any operating system dependent initializations you'd like */
>          OsInit();
>          if (serverGeneration == 1) {
> diff --git a/include/dix.h b/include/dix.h
> index 240018b..3e3a672 100644
> --- a/include/dix.h
> +++ b/include/dix.h
> @@ -240,10 +240,9 @@ extern _X_EXPORT void RemoveBlockAndWakeupHandlers(ServerBlockHandlerProcPtr blo
>  
>  extern _X_EXPORT void InitBlockAndWakeupHandlers(void);
>  
> +extern _X_EXPORT Bool InitWorkQueue(void);
>  extern _X_EXPORT void ProcessWorkQueue(void);
> -
>  extern _X_EXPORT void ProcessWorkQueueZombies(void);
> -
>  extern _X_EXPORT Bool QueueWorkProc(Bool (*function)(ClientPtr clientUnused,
>                                                       void *closure),
>                                      ClientPtr client,
> -- 
> 2.9.3
> 
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