1a8f3a368f
There's a rare TOCTOU case that happens from time to time with maxconn 1 and multiple threads. Between the moment we see the queue full and the moment we queue a request, it's possible that the last request on the server or proxy ended and that no other one is left to offer it its place. Given that all this code path is performance-critical and we cannot afford to increase the lock duration, better recheck for the condition after queueing. For this we need to be able to check for the condition and cleanly dequeue a request. That's what this patch provides via the new function pendconn_must_try_again(). It will catch more requests than absolutely needed though it will catch them all. It may find that around 1/1000 of requests are at risk, though testing shows that in practice, it's around 1 per million that really gets stuck (other ones benefit from timing and finishing late requests). Maybe in the future some conditions might be refined but it's harmless. What happens to such requests is that they're dequeued and their pendconn freed, so that the caller can decide to try to LB or queue them again. For now the function is not used, it's just added separately for easier tracking.
HAProxy
HAProxy is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
Installation
The INSTALL file describes how to build HAProxy. A list of packages is also available on the wiki.
Getting help
The discourse and the mailing-list are available for questions or configuration assistance. You can also use the slack or IRC channel. Please don't use the issue tracker for these.
The issue tracker is only for bug reports or feature requests.
Documentation
The HAProxy documentation has been split into a number of different files for ease of use. It is available in text format as well as HTML. The wiki is also meant to replace the old architecture guide.
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)
License
HAProxy is licensed under GPL 2 or any later version, the headers under LGPL 2.1. See the LICENSE file for a more detailed explanation.