vefd: Thin wrapper around eventfd with pipe emulation #4348
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This is a minimal API not attempting to keep track of the eventfd counter, and only caring about threads signalling progress on one end, and another thread being able to notice that progress can be made. This is an alternative to condvars when waiting for progress will content with polling concurrently waiting for progress elsewhere. Since locks/condvars don't compose well with file descriptors, the VEFD API offers an alternative that can integrate an existing poll on other file descriptors.
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bugwash consensus: wait for h2 patch which uses this to make a judgement if it can be avoided |
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We recently made change to the HTTP/2 implementation in Varnish Enterprise and would like to share this change. The new HTTP/2 architecture relies on a non-portable
eventfd()notification system over a file descriptor, to enable polling of both the client socket andh2_reqthreads notifications simultaneously from theh2_sessthread.We settled on this minimal API to capture our limited
eventfd()usage and added a fallback topipe()decided at configure time for systems withouteventfd()support.