[dropping bug-automake, adding autoconf-patches] References: <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9245> <http://www.freebsd.org/cgi/query-pr.cgi?pr=159730>
On Tuesday 16 August 2011, Stefano Lattarini wrote: > Hi Eric. > > On Tuesday 16 August 2011, Eric Blake wrote: > > On 08/16/2011 10:04 AM, Stefano Lattarini wrote: > > > The "proper fix" is even easier BTW: just use "$$exit || exit 1" instead. > > > > > > The updated patch should now work (and I've tested it properly this time). > > > This new patch hasn't been derived by "cargo-cult guessing", but from the > > > explanation of the relevant FreeBSD make bug provided by Jilles Tjoelker: > > > <http://www.freebsd.org/cgi/query-pr.cgi?pr=159730> > > > > > > Now that's something to be documented in the Autoconf manual I'd say ... > > > > Indeed. So it all boils down to BSD make rewriting rules (but only for > > make -j) to be roughly: > > > > sh -c 'set -v; your rules; set +v' > > > > and losing your exit status (not to mention sharing shell status between > > commands that are supposed to be in independent shells), when it really > > should have been rewriting as something more complex: > > > > sh -c '(your rule 1); (your rule 2); st=$?; set +v; exit $st' > > > > And your workaround of an explicit exit rather than relying on $? at the > > end of your 'set +e' invocation is indeed the proper way to force the > > parallel make bug to be avoided, by exiting prior to any post-commands > > injected by the BSD make rewriting going on that corrupt $?. > > > I'll have a "draft patch" read soonish. There is ample room for improvements, > but I'll post it here anyway since it can benefit from early feedback. > Here it is. As usual, comments and suggestions welcome. Regards, Stefano
From a60b30ea47b2cc36d0b85bbed94a106643fba745 Mon Sep 17 00:00:00 2001 Message-Id: <a60b30ea47b2cc36d0b85bbed94a106643fba745.1313513383.git.stefano.lattar...@gmail.com> From: Stefano Lattarini <stefano.lattar...@gmail.com> Date: Tue, 16 Aug 2011 18:31:42 +0200 Subject: [PATCH] docs: other issues with parallel BSD make Motivated by automake bug#9245: <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9245> and FreeBSD PR bin/159730: <http://www.freebsd.org/cgi/query-pr.cgi?pr=159730> * doc/autoconf.texi (Parallel Make): Document other BSD make incompatibilities. Reorganize the existing related documentation accordingly. --- ChangeLog | 11 ++++ doc/autoconf.texi | 137 +++++++++++++++++++++++++++++++++++----------------- 2 files changed, 103 insertions(+), 45 deletions(-) diff --git a/ChangeLog b/ChangeLog index 6ca51fd..6e36455 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,14 @@ +2011-08-16 Stefano Lattarini <stefano.lattar...@gmail.com> + + docs: other issues with parallel BSD make + Motivated by automake bug#9245: + <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9245> + and FreeBSD PR bin/159730: + <http://www.freebsd.org/cgi/query-pr.cgi?pr=159730> + * doc/autoconf.texi (Parallel Make): Document other BSD make + incompatibilities. Reorganize the existing related documentation + accordingly. + 2011-08-08 Stefano Lattarini <stefano.lattar...@gmail.com> docs: fix minor typos diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 7c1818d..b2b0a59 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -19826,45 +19826,10 @@ sh Support for parallel execution in @command{make} implementation varies. Generally, using GNU make is your best bet. -Some make implementations (among them, FreeBSD @command{make}, NetBSD -@command{make}, and Solaris @command{dmake}), when invoked with a -@option{-j@var{N}} option, connect the standard output and standard -error of all their child processes to pipes or temporary regular -files. This can lead to subtly different semantics in the behaviour -of the spawned processes. For example, even if the @command{make} -standard output is connected to a tty, the recipe command will not be: - -@example -$ @kbd{cat Makefile} -all: - @@test -t 1 && echo "Is a tty" || echo "Is not a tty" -$ @kbd{make -j 2} # FreeBSD make -Is not a tty -$ @kbd{make -j 2} # NetBSD make ---- all --- -Is not a tty -$ @kbd{dmake -j 2} # Solaris dmake -@var{hostname} --> 1 job -@var{hostname} --> Job output -Is not a tty -@end example - -@noindent -On the other hand: - -@example -$ @kbd{make -j 2} # GNU make, Heirloom make -Is a tty -@end example - -Furthermore, parallel runs of those @command{make} implementations will -route standard error from commands that they spawn into their own -standard output, and may remove leading whitespace from output lines. - When NetBSD or FreeBSD @command{make} are run in parallel mode, they will reuse the same shell for multiple commands within one recipe. This can -have unexpected consequences. For example, change of directories or -variables persist between commands: +have various unexpected consequences. For example, changes of directories +or variables persist between recipes, so that: @example all: @@ -19876,7 +19841,6 @@ all: may output the following with @code{make -j1}: @example ---- all --- / value 32235 @@ -19897,19 +19861,102 @@ value 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. +@noindent +Another consequence 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 produced by NetBSD -@command{make} (but @emph{not} by FreeBSD @command{make}) in parallel -mode for targets being updated. +The BSD @command{make} implementations, when run in parallel mode, +will also pass the @command{Makefile} recipes to the shell through +its standard input, thus making it unusable from the recipes: -You can avoid these issues by using the @option{-B} option to enable +@example +$ @kbd{cat Makefile} +read: + @@read line; echo LINE: $$line +@c $$ @c restore font-lock +$ @kbd{echo foo | make read} +LINE: foo +$ @kbd{echo foo | make -j1 read} +LINE: +@end example + +@noindent +Moreover, when FreeBSD @command{make} is run in parallel mode, it +implements the @code{@@} and @code{-} ``recipe modifiers'' by dynamically +modifying the active shell flags. This behaviour has the effects of +potentially clobbering the exit status of recipes silenced with the +@code{@@} modifier if they also unset the @option{errexit} shell flag, +and of mangling the output in unexpected ways: + +@example +$ @kbd{cat Makefile} +a: + @@echo $$-; set +e; false +b: + -echo $$-; false; echo set - +$ @kbd{make a; echo status: $?} +ehBc +*** Error code 1 +status: 1 +$ @kbd{make -j1 a; echo status: $?} +ehB +status: 0 +$ @kbd{make b} +echo $-; echo set - +hBc +set - +$ @kbd{make -j1 b} +echo $-; echo hvB +@end example + +@noindent +You can avoid all these issues by using the @option{-B} option to enable compatibility semantics. However, that will effectively also disable all parallelism as that will cause prerequisites to be updated in the order they are listed in a rule. +Some make implementations (among them, FreeBSD @command{make}, NetBSD +@command{make}, and Solaris @command{dmake}), when invoked with a +@option{-j@var{N}} option, connect the standard output and standard +error of all their child processes to pipes or temporary regular +files. This can lead to subtly different semantics in the behaviour +of the spawned processes. For example, even if the @command{make} +standard output is connected to a tty, the recipe command will not be: + +@example +$ @kbd{cat Makefile} +all: + @@test -t 1 && echo "Is a tty" || echo "Is not a tty" +$ @kbd{make -j 2} # FreeBSD make +Is not a tty +$ @kbd{make -j 2} # NetBSD make +--- all --- +Is not a tty +$ @kbd{dmake -j 2} # Solaris dmake +@var{hostname} --> 1 job +@var{hostname} --> Job output +Is not a tty +@end example + +@noindent +On the other hand: + +@example +$ @kbd{make -j 2} # GNU make, Heirloom make +Is a tty +@end example + +@noindent +The above examples also show additional status output produced in parallel +mode for targets being updated by Solaris @command{dmake} and NetBSD +@command{make} (but @emph{not} by FreeBSD @command{make}). + +Furthermore, parallel runs of those @command{make} implementations will +route standard error from commands that they spawn into their own +standard output, and may remove leading whitespace from output lines. + + @node Comments in Make Rules @section Comments in Make Rules @cindex Comments in @file{Makefile} rules -- 1.7.2.3
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