windows – Git如何从UNC路径获取更改？

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compat / poll：睡眠1毫秒,以避免繁忙的等待

SwitchToThread() only gives away the rest of the current time slice to another thread in the current process. So if the thread that feeds the file decscriptor we’re polling is not in the current process,we get busy-waiting.

I played around with this quite a bit. After trying some more complex schemes,I found that what worked best is to just sleep 1 millisecond between iterations. Though it’s a very short time,it still completely eliminates the busy wait condition,without hurting perf.

There code uses SleepEx(1,TRUE) to sleep.
See 07002 for a good discussion of why that is better than calling SwitchToThread,which is what was used previously:

Note that calling SleepEx(0,TRUE) does not solve the busy wait.

The most striking case was when testing on a UNC share with a large repo,on a single CPU machine.
Without the fix,it took 4 minutes 15 seconds,and with the fix it took just 1:08! I think it’s because git-upload-pack‘s busy wait was eating the CPU away from the git process that’s doing the real work. With multi-proc,the timing is not much different,but tons of CPU time is still wasted,which can be a killer on a server that needs to do bunch of other things.