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Re: [libvirt] [PATCH 01/10] util: Introduce thread queues




On 05/21/2015 06:42 PM, Jiri Denemark wrote:
> Our usage of pthread conditions does not allow a single thread to wait
> for several events from different sources. This is because the condition
> is bound to the source of the event. We can invert the usage by giving
> each thread its own condition and providing APIs for registering this
> thread condition with several sources. Each of the sources can then
> signal the thread condition.
> 
> Thread queues also support several threads to be registered with a
> single event source, which can either wakeup all waiting threads or just
> the first one.
> 
> Signed-off-by: Jiri Denemark <jdenemar redhat com>
> ---
>  po/POTFILES.in            |   1 +
>  src/Makefile.am           |   2 +
>  src/libvirt_private.syms  |  15 ++
>  src/util/virthreadqueue.c | 343 ++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/virthreadqueue.h |  54 ++++++++
>  5 files changed, 415 insertions(+)
>  create mode 100644 src/util/virthreadqueue.c
>  create mode 100644 src/util/virthreadqueue.h
> 

Ran the series through Coverity and came back with this gem

> +
> +void
> +virThreadQueueFree(virThreadQueuePtr queue)
> +{
> +    if (!queue)
> +        return;
> +
> +    while (queue->head)
> +        virThreadQueueRemove(queue, queue->head);

(3) Event cond_true: 	Condition "queue->head", taking true branch
(6) Event loop_begin: 	Jumped back to beginning of loop
(7) Event cond_true: 	Condition "queue->head", taking true branch

283  	    while (queue->head)

(4) Event freed_arg: 	"virThreadQueueRemove" frees "queue->head". [details]
(5) Event loop: 	Jumping back to the beginning of the loop
(8) Event deref_arg: 	Calling "virThreadQueueRemove" dereferences freed pointer "queue->head". [details]

284  	        virThreadQueueRemove(queue, queue->head);

> +    VIR_FREE(queue);
> +}
> +
> +


Where the link to [details] has:

230  	static void
231  	virThreadQueueRemove(virThreadQueuePtr queue,
232  	                     virThreadQueueItemPtr item)
233  	{

(1) Event cond_true: 	Condition "item->prev", taking true branch
(1) Event deref_parm: 	Directly dereferencing parameter "item".
Also see events: 	[freed_arg]

234  	    if (item->prev)

(2) Event if_fallthrough: 	Falling through to end of if statement

235  	        item->prev->next = item->next;
236  	    else

(3) Event if_end: 	End of if statement

237  	        queue->head = item->next;
238  	

(4) Event cond_true: 	Condition "item->next", taking true branch

239  	    if (item->next)

(5) Event if_fallthrough: 	Falling through to end of if statement

240  	        item->next->prev = item->prev;
241  	    else

(6) Event if_end: 	End of if statement

242  	        queue->tail = item->prev;
243  	
244  	    virObjectUnref(item->cond);

(7) Event freed_arg: 	"virFree" frees parameter "item". [details]

245  	    VIR_FREE(item);
246  	}
247  	


John


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