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Diffstat (limited to 'doc/make.texi')
| -rw-r--r-- | doc/make.texi | 27 |
1 files changed, 24 insertions, 3 deletions
diff --git a/doc/make.texi b/doc/make.texi index dffa14d..1a760e1 100644 --- a/doc/make.texi +++ b/doc/make.texi @@ -4057,9 +4057,12 @@ If there is nothing looking like an integer after the @samp{-j} option, there is no limit on the number of job slots. The default number of job slots is one, which means serial execution (one thing at a time). -One unpleasant consequence of running several recipes simultaneously is -that output generated by the recipes appears whenever each recipe -sends it, so messages from different recipes may be interspersed. +One consequence of running several recipes simultaneously is that by +default, output from each recipe appears as soon as it is generated, +with the result that messages from different recipes may be interspersed. +This may create problems in interpreting output. If the @samp{-P} option +is used, however, recipes will save their output until completion and +then take turns writing it, with a more coherent result. Another problem is that two processes cannot both take input from the same device; so to make sure that only one recipe tries to take input @@ -8612,6 +8615,24 @@ The data base output contains file name and line number information for recipe and variable definitions, so it can be a useful debugging tool in complex environments. +@item -P +@cindex @code{-P} +@itemx --parallel-sync +@cindex @code{--parallel-sync} +@cindex parallel recipe execution, output +When jobs are running in parallel under @samp{--jobs}, the output of +each job is held until the job is complete thus ensuring that the output +of each recipe is grouped together. + +With no argument or the argument @samp{1}, messages from each job in +recursive makes are grouped together. With the argument @samp{2}, the +complete output from any recursive make is grouped together. The latter +achieves better grouping of output from related jobs, but causes longer +delay, since messages do not appear until the recursive make has +completed. Therefore @samp{-P} is more useful when watching the output +while make runs, and @samp{-P2} is better suited when running a complex +parallel build in the background and checking its output afterwards. + @item -q @cindex @code{-q} @itemx --question |