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HAProxy - Load balancer
d5402b8df8
There's a theoretical race (that we failed to trigger) in function fd_update_events(), which could strike on idle connections. The "locked" variable will most often be 0 as the FD is bound to the current thread only. Another thread could take it over once "locked" is set, change the thread and running masks. Then the first thread updates the FD's state non-atomically and possibly overwrites what the other thread was preparing. It still looks like the FD's state will ultimately converge though. The solution against this is to set the running flag earlier so that a takeover() attempt cannot succeed, or that the fd_set_running() attempt fails, indicating that nothing needs to be done on this FD. While this is sufficient for a simple fix to be backported, it leaves the FD actively polled in the calling thread, this will trigger a second wakeup which will notice the absence of tid_bit in the thread_mask, getting rid of it. A more elaborate solution would consist in calling fd_set_running() directly from the pollers before calling fd_update_events(), getting rid of the thread_mask test and letting the caller eliminate that FD from its list if needed. Interestingly, this code also proves to be suboptimal in that it sets the FD state twice instead of calculating the new state at once and always using a CAS to set it. This is a leftover of a simplification that went into 2.4 and which should be explored in a future patch. This may be backported as far as 2.2. |
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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)