Building on Windows takes a very long time

[EZabolotniy]

On Windows, when Ninja creates a Subprocess to compile a file, it redirects the Subprocess's std::out and std::err to read dependencies from it:

startup_info.hStdOutput = child_pipe;
startup_info.hStdError = child_pipe;

I am using a custom compiler that, after compiling a file, prints the dependencies to std::err. In my case, printing to std::err might take about 2-3 seconds.
I tried to exclude Ninja from the process of reading from std::err by redirecting the Subprocess's std:: err to nul:

startup_info.hStdError = nul;

With this change, writing to std::err only takes a few microseconds.

Is there a way to fix this issue and improve interprocess communication speed on Windows?

[jhasse]

How much data does the compiler print? 2-3 seconds sound like a lot. Is the time spent in capturing the output or actually reprinting it on the console (this is slow on Windows)?

[digit-google]

It would help tremendously if you could provide a simple reproduction case, i.e. a fake compiler program that outputs fake dependencies, and a related Ninja build plan, that shows the problem clearly.