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Diffstat (limited to 'src/lib/thread/threading.md')
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diff --git a/src/lib/thread/threading.md b/src/lib/thread/threading.md new file mode 100644 index 0000000000..a1058c97de --- /dev/null +++ b/src/lib/thread/threading.md @@ -0,0 +1,26 @@ + +@page threading Threading in Tor + +Tor is based around a single main thread and one or more worker +threads. We aim (with middling success) to use worker threads for +CPU-intensive activities and the main thread for our networking. +Fortunately (?) we have enough cryptography that moving what we can +of the cryptographic processes to the workers should achieve good +parallelism under most loads. Unfortunately, we only have a small +fraction of our cryptography done in our worker threads right now. + +Our threads-and-workers abstraction is defined in workqueue.c, which +combines a work queue with a thread pool, and integrates the +signalling with libevent. Tor's main instance of a work queue is +instantiated in cpuworker.c. It will probably need some refactoring +as more types of work are added. + +On a lower level, we provide locks with tor_mutex_t in \refdir{lib/lock}, and +higher-level locking/threading tools in \refdir{lib/thread}, including +conditions (tor_cond_t), thread-local storage (tor_threadlocal_t), and more. + + +Try to minimize sharing between threads: it is usually best to simply +make the worker "own" all the data it needs while the work is in +progress, and to give up ownership when it's complete. + |