Support v7 log format #122
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The future log format will be using rapidhash instead of murmurhash in order to calculate the hash of the build command. In order not to break in the future we add support now for when the next version of ninja is released. Unfortunately this means that we need to save the whole build command when parsing instead of generating the hash and discarding the string. This is because we can only locate the `.ninja_log` file once we parse the entire ninja build file to look for any `builddir` variables. Then only once we have the directory can we attempt to load the `.ninja_log` file to figure out which hash function it uses. However, after this change we now get a small performance benefit when there is no `.ninja_log` file or when it contains entries that don't now exist in the ninja build file because we only hash the current build command if necessary. In order to try and reduce some of the extra work we do, this commit also changes the `LogReader` constructor to pass a bitfield on what fields we want to read. In our case this saves us having to decipher the start, end, and modification times of each entry, which we don't need. There are a lot of conditionals here, but they should be predicted by the branch predictor and so changing them to a template paramater isn't needed right now.
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Add support after ninja-build/ninja#2519 |
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The future log format will be using rapidhash instead of murmurhash in order to calculate the hash of the build command. In order not to break in the future we add support now for when the next version of ninja is released.
Unfortunately this means that we need to save the whole build command when parsing instead of generating the hash and discarding the string. This is because we can only locate the
.ninja_logfile once we parse the entire ninja build file to look for anybuilddirvariables. Then only once we have the directory can we attempt to load the.ninja_logfile to figure out which hash function it uses.However, after this change we now get a small performance benefit when there is no
.ninja_logfile or when it contains entries that don't now exist in the ninja build file because we only hash the current build command if necessary.In order to try and reduce some of the extra work we do, this commit also changes the
LogReaderconstructor to pass a bitfield on what fields we want to read. In our case this saves us having to decipher the start, end, and modification times of each entry, which we don't need. There are a lot of conditionals here, but they should be predicted by the branch predictor and so changing them to a template paramater isn't needed right now.