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The current principle of running under isolation was made to access sensitive data while being certain that no other thread was using them in parallel, without necessarily having to place locks everywhere. The main use case are "show sess" and "show fd" which run over long chains of pointers. The thread_isolate() call relies on the "harmless" bit that indicates for a given thread that it's not currently doing such sensitive things, which is advertised using thread_harmless_now() and which ends usings thread_harmless_end(), which also waits for possibly concurrent threads to complete their work if they took this opportunity for starting something tricky. As some system calls were notoriously slow (e.g. mmap()), a bunch of thread_harmless_now() / thread_harmless_end() were placed around them to let waiting threads do their work while such other threads were not able to modify memory contents. But this is not sufficient for performing memory modifications. One such example is the server deletion code. By modifying memory, it not only requires that other threads are not playing with it, but are not either in the process of touching it. The fact that a pool_alloc() or pool_free() on some structure may call thread_harmless_now() and let another thread start to release the same object's memory is not acceptable. This patch introduces the concept of "idle threads". Threads entering the polling loop are idle, as well as those that are waiting for all others to become idle via the new function thread_isolate_full(). Once thread_isolate_full() is granted, the thread is not idle anymore, and it is released using thread_release() just like regular isolation. Its users have to keep in mind that across this call nothing is granted as another thread might have performed shared memory modifications. But such users are extremely rare and are actually expecting this from their peers as well. Note that that in case of backport, this patch depends on previous patch: MINOR: threads: make thread_release() not wait for other ones to complete |
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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)