When would you want to force a thread?

We have seen that threads are created by elements but it is also possible to insert elements in the pipeline for the sole purpose of forcing a new thread in the pipeline.

There are several reasons to force the use of threads. However, for performance reasons, you never want to use one thread for every element out there, since that will create some overhead. Let's now list some situations where threads can be particularly useful:

Above, we've mentioned the queue element several times now. A queue is the thread boundary element through which you can force the use of threads. It does so by using a classic provider/consumer model as learned in threading classes at universities all around the world. By doing this, it acts both as a means to make data throughput between threads threadsafe, and it can also act as a buffer. Queues have several GObject properties to be configured for specific uses. For example, you can set lower and upper thresholds for the element. If there's less data than the lower threshold (default: disabled), it will block output. If there's more data than the upper threshold, it will block input or (if configured to do so) drop data.

To use a queue (and therefore force the use of two distinct threads in the pipeline), one can simply create a queue element and put this in as part of the pipeline. GStreamer will take care of all threading details internally.