NAME

       makeparallel - command line tool for communication with the GNU make jobserver

SYNOPSIS

       To run a multi-thread or multi-process binary inside GNU make using makeparallel, add:

                  +makeparallel subprocess arguments

       to a rule.  For example, to wrap ninja in make, use something like:

                  +makeparallel ninja -f build.ninja

       To determine the size of the jobserver pool, add:

                  +makeparallel echo > make.jobs

       to  a rule that is guarantee to run alone (i.e. all other rules are either dependencies of the makeparal‐
       lel rule, or the depend on the makeparallel rule.  The output file will contain the -j<num>  flag  passed
       to the parent make process, or -j1 if no flag was found.  Since GNU make will run makeparallel during the
       execution phase, after all variables have been set and evaluated, it is not possible to get the output of
       makeparallel into a make variable.  Instead, use a shell substitution to read the output file directly in
       a recipe.  For example:

                  echo Make was started with $$(cat make.jobs)

DESCRIPTION

       makeparallel communicates with the GNU make jobserver (http://make.mad-scientist.net/papers/jobserver-im‐
       plementation/)  in  order  claim all available jobs, and then passes the number of jobs claimed to a sub‐
       process with -j<jobs>.

       The number of available jobs is determined by reading tokens from the jobserver until a read would block.
       If the makeparallel rule is the only one running the number of jobs will be the total size  of  the  job‐
       server  pool, i.e. the value passed to make with -j.  Any jobs running in parallel with with the makepar‐
       ellel rule will reduce the measured value, and thus reduce the parallelism available to the subprocess.

AUTHORS

       The Android Open Source Project.

                                                                                                 MAKEPARALLEL(1)