use -j; all make's in a recursive build cooperate to limit the total
number of jobs, using a token-passing scheme.
The current token passing algorithm is similar to the one implemented
by gmake; there is a single pipe which is inherited through the entire
process hierarchy; tokens are obtained by reading a byte from the
"read end" of the pipe, and are returned by writing them to the "write
end". This exact algorithm is likely to change in the future.
Implementation details:
- Use the new trace facility to allow measurement of the
effectiveness of different token-passing schemes
- Get a token in MakeStartJobs(), return it in Make_Update()
- Eliminate Job_Full() and the jobFull global since they are
redundant with token system.
- Add an "internal" -J option (to pass the token pipe fd's down to
submakes) and a -T option for tracing.
- Change how compatMake is forced so that -j means something when
inherited by submakes.
- When waiting for a token, poll the token-passing pipe as well as
the output pipes of existing jobs.
poll() for parallel make:
- Make the poll() code behave more like the select() code: sleep for
a bit waiting for output rather than busy-wait (eww).
- Install a no-op SIGCHLD handler so that poll/select wake up early
(with -1/EINTR) when a child exits.
- Change the default sleep time from 500ms to 5 seconds since we now
wake up promptly when a child exits.
Unfortunately this revealed a deeper problem with the brk_string code.
To fix it:
- remove sharing of the buffer between brk_string invocations
- change the semantics of brk_string so that the argument array
starts with 0, and return the buffer where the strings are
stored
sommerfeld