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Right now we're using a DWCAS to atomically set the running_mask while being constrained by the thread_mask. This DWCAS is annoying because we may seriously need it later when adding support for thread groups, for checking that the running_mask applies to the correct group. It turns out that the DWCAS is not strictly necessary because we never need it to set the thread_mask based on the running_mask, only the other way around. And in fact, the running_mask is always cleared alone, and the thread_mask is changed alone as well. The running_mask is only relevant to indicate a takeover when the thread_mask matches it. Any bit set in running and not present in thread_mask indicates a transition in progress. As such, it is possible to re-arrange this by using a regular CAS around a consistency check between running_mask and thread_mask in fd_update_events and by making a CAS on running_mask then an atomic store on the thread_mask in fd_takeover(). The only other case is fd_delete() but that one already sets the running_mask before clearing the thread_mask, which is compatible with the consistency check above. This change has happily survived 10 billion takeovers on a 16-thread machine at 800k requests/s. The fd-migration doc was updated to reflect this change.
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)