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New manual section `Parallel Make'.

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* doc/autoconf.texi (Parallel Make): New node, document NetBSD
`make -jN' quirks.
(Top, Portable Make): Adjust menus.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
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Ralf Wildenhues 2009-05-17 11:49:44 +02:00
parent 83d976a33f
commit b29a07fffb
2 changed files with 69 additions and 0 deletions
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@ -1,3 +1,10 @@
2009-05-17 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
New manual section `Parallel Make'.
* doc/autoconf.texi (Parallel Make): New node, document NetBSD
`make -jN' quirks.
(Top, Portable Make): Adjust menus.
2009-05-14 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
testsuite: skip `Multiple languages' test without C++ compiler.

62
doc/autoconf.texi
View File

@ -509,6 +509,7 @@ Portable Make Programming
* Macros and Submakes:: @code{make macro=value} and submakes
* The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues
* The Make Macro SHELL:: @code{$(SHELL)} portability issues
* Parallel Make:: Parallel @command{make} quirks
* Comments in Make Rules:: Other problems with Make comments
* obj/ and Make:: Don't name a subdirectory @file{obj}
* make -k Status:: Exit status of @samp{make -k}
@ -17567,6 +17568,7 @@ itself.
* Macros and Submakes:: @code{make macro=value} and submakes
* The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues
* The Make Macro SHELL:: @code{$(SHELL)} portability issues
* Parallel Make:: Parallel @command{make} quirks
* Comments in Make Rules:: Other problems with Make comments
* obj/ and Make:: Don't name a subdirectory @file{obj}
* make -k Status:: Exit status of @samp{make -k}
@ -17878,6 +17880,66 @@ $ @kbd{env SHELL=sh gmake -e SHELL=/bin/ksh} # GNU make 3.81
sh
@end example
@node Parallel Make
@section Parallel Make
@cindex Parallel @command{make}
Support for parallel execution in @command{make} implementation varies.
Generally, using @acronym{GNU} make is your best bet. When NetBSD
@command{make} is invoked with @option{-j@var{N}}, it will reuse the
same shell for multiple commands within one recipe. This can have
unexpected consequences.@footnote{Note that @acronym{GNU} make has
heuristics to avoid spawning a shell at all if the command is deemed
safe to be executed directly.} For example, change of directories or
variables persist between commands:
@example
all:
@@var=value; cd /; pwd; echo $$var; echo $$$$
@@pwd; echo $$var; echo $$$$
@end example
@noindent
may output the following with @code{make -j1}:
@example
--- all ---
/
value
32235
/
value
32235
@end example
while without @option{-j1}, or with @option{-B}, the output looks less
surprising:
@example
/
value
32238
/tmp
32239
@end example
Another consequence of this is that, if one command in a recipe uses
@code{exit 0} to indicate a successful exit, the shell will be gone
and the remaining commands of this recipe will not be executed.
The above example also shows additional status output NetBSD
@command{make} produces in parallel mode for targets being updated.
Furthermore, parallel NetBSD @command{make} will route standard error
from commands that it spawns into its own standard output, and may
remove leading whitespace from output lines.
You can avoid these issues by using the @option{-B} option to enable
compatibility semantics. However, that will effectively also disable
all parallelism as that will cause prerequisites to be updated in the
order they are listed in a rule.
@node Comments in Make Rules
@section Comments in Make Rules
@cindex Comments in @file{Makefile} rules