%% Peter Keitler <[EMAIL PROTECTED]> writes:
pk> the following Makefile enters an endless loop on our Cygwin installation
pk> (Win2k, SP3) with GNU Make 3.80.
pk> ### begin
pk> dep : env
pk> @echo Target: dep
pk> touch dep
pk> env:
pk> @echo Target: environment
pk> include dep
pk> ### end
pk> I call it with the 'make' command only, without any parameters. On
pk> our Linux box (SuSE 8.1, 'uname -r: 2.4.21-168-default') with GNU
pk> Make Version 3.79.1, both targets are built only twice each. This
pk> is the behaviour I would expect, since the included Makefile has
pk> changed after the first run.
Actually you're just lucky that it only builds twice on Linux; it
probably is due to the coarseness of the timestamp and how fast Linux is
at re-execing. It should build over and over on Linux as well.
Your problem is that you never create the "env" file. Because that file
is never created, it's always considered out-of-date and its command is
always invoked. Because env is always out-of-date, dep (which depends
on env) is always considered out of date out-of-date as well. Because
dep is always out-of-date, it's always rebuilt, and because it's always
rebuilt, make always re-execs.
On Linux, the re-exec and re-parsing of the makefile are so fast that
even after it re-execs, re-reads the makefile, and re-runs the dep rule,
the timestamp on the file is _STILL_ identical (to the second) to the
last time make ran it. Since make relies solely on timestamps it thinks
you didn't actually update the dep file and doesn't consider it
modified, so it doesn't re-exec.
If you time it just right you could get it to run three times, since the
second would tick over between the first and second invocations. Or, if
you move to any filesystem that supports sub-second timestamps you'll
see this go into an infinite loop.
The only solution is to create the env file:
dep : env
@echo Target: dep
touch dep
env:
@echo Target: environment
touch env
include dep
Note this will run "env" only once, not twice.
--
-------------------------------------------------------------------------------
Paul D. Smith <[EMAIL PROTECTED]> Find some GNU make tips at:
http://www.gnu.org http://make.paulandlesley.org
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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