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When built with USE_MEMORY_PROFILING the main memory allocation functions are diverted to collect statistics per caller. It is a bit tricky because the only way to call the original ones is to find their pointer, which requires dlsym(), and which is not available everywhere. Thus all functions are designed to call their fallback function (the original one), which is preset to an initialization function that is supposed to call dlsym() to resolve the missing symbols, and vanish. This saves expensive tests in the critical path. A second problem is that dlsym() calls calloc() to initialize some error messages. After plenty of tests with posix_memalign(), valloc() and friends, it turns out that returning NULL still makes it happy. Thus we currently use a visit counter (in_memprof) to detect if we're reentering, in which case all allocation functions return NULL. In order to convert a return address to an entry in the stats, we perform a cheap hash consisting in multiplying the pointer by a balanced number (as many zeros as ones) and keeping the middle bits. The hash is already pretty good like this, achieving to store up to 638 entries in a 2048-entry table without collision. But in order to further refine this and improve the fill ratio of the table, in case of collision we move up to 16 adjacent entries to find a free place. This remains quite cheap and manages to store all of these inside a 1024-entries hash table with even less risk of collision. Also, free(NULL) does not produce any stats. By doing so we reduce from 638 to 208 the average number of entries needed for a basic config using SSL. free(NULL) not only provides no information as it's a NOP, but keeping it is pure pollution as it happens all the time. When DEBUG_MEM_STATS is enabled, malloc/calloc/realloc are redefined as macros, preventing the code from compiling. Thus, when this option is detected, the macros are undefined as they are pointless there anyway. The functions are optimized to quickly jump to the fallback and as such become almost invisible in terms of processing time, execpt an extra "if" on a read_mostly variable and a jump. Considering that this only happens for pool misses and library routines, this remains acceptable. Performance tests in SSL (the most stressful test) shows less than 1% performance loss when profiling is enabled on 2c4t. The code was written in a way to ease backporting to modern versions (2.2+) if needed, so it keeps the long names for integers and doesn't use the _INC version of the atomic ops.
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)