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These functions need to set/reset the FD's tgid but when they're called there may still be wakeups on other threads that discover late updates and have to touch the tgid at the same time. As such, it is not possible to just read/write the tgid there. It must only be done using operations that are compatible with what other threads may be doing. As we're using inc/dec on the refcount, it's safe to AND the area to zero the lower part when resetting the value. However, in order to set the value, there's no other choice but fd_claim_tgid() which will assign it only if possible (via a CAS). This is convenient in the end because it protects the FD's masks from being modified by late threads, so while we hold this refcount we can safely reset the thread_mask and a few other elements. A debug test for non-null masks was added to fd_insert() as it must not be possible to face this situation thanks to the protection offered by the tgid.
The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)