[bug #26864] make -j2 fails to rebuild intermediate file

[Manoj Srivastava]

URL:
  <http://savannah.gnu.org/bugs/?26864>

                 Summary: make -j2 fails to rebuild intermediate file
                 Project: make
            Submitted by: srivasta
            Submitted on: Sun 21 Jun 2009 12:04:03 PM CDT
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.81
        Operating System: POSIX-Based
           Fixed Release: None

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Details:


        This was reported by a Debian user.  Here is how to reproduce the
problem:

cat >Makefile <<"EOF"
# .bar files depend on .c files as well as foo.h
%.bar: %.c foo.h
        cat $^ >$@ || rm $@

# foo.h is created from foo.in
foo.h: foo.h.in
        cat $^ >$@ || rm $@

# main.c should be created from main.y  below
EOF

cat >main.y <"EOF"
%%
command:
      "q"                     { return 1; }
      ;
%%
EOF

echo bar >foo.h.in

# The initial build is fine
make -j2 main.bar
  cat foo.h.in >foo.h || rm foo.h
  yacc  main.y 
  mv -f y.tab.c main.c
  cat main.c foo.h >main.bar || rm main.bar
  rm main.c

# But touch foo.h.in and things go wrong
touch foo.h.in
make -j2 main.bar
  cat foo.h.in >foo.h || rm foo.h
  cat main.c foo.h >main.bar || rm main.bar
  cat: main.c: No such file or directory

# Here 'make -j2' decides to rebuild main.bar without first 
# recreating main.c although we explicitly stated that main.bar
# depends on main.c. Here is what that command says with -d:

  Considering target file `main.bar'.
     Considering target file `main.y'.          <--- Should be main.c
     File `main.y' was considered already.
    Considering target file `foo.h'.
    File `foo.h' was considered already.
   Pruning file `main.c'.                                     <--- ???
   Finished prerequisites of target file `main.bar'.
   Prerequisite `main.c' of target `main.bar' does not exist. <--- !!!
   Prerequisite `foo.h' is newer than target `main.bar'.
  Must remake target `main.bar'.
  cat main.c foo.h >main.bar || rm main.bar
  cat: main.c: No such file or directory                      <--- Doh!

# The next attempt works though (but this time make does not 
# have to rebuild foo.h)
make -j2 main.bar
  yacc  main.y 
  mv -f y.tab.c main.c
  cat main.c foo.h >main.bar || rm main.bar
  rm main.c

# Compare this with 'make -j1'
touch foo.h.in
make -j1 main.bar
  cat foo.h.in >foo.h || rm foo.h
  yacc  main.y 
  mv -f y.tab.c main.c
  cat main.c foo.h >main.bar || rm main.bar
  rm main.c

# Here make correctly realizes it must rebuild main.c before attempting 
# to run the command to generate main.bar. And the corresponding make 
# -d output:

     Prerequisite `foo.h.in' is newer than target `foo.h'.
    Must remake target `foo.h'.
  cat foo.h.in >foo.h || rm foo.h
    Successfully remade target file `foo.h'.
   Considering target file `main.c'.        <--- Correct target
    File `main.c' does not exist.
     Pruning file `main.y'.
    Finished prerequisites of target file `main.c'.
   Must remake target `main.c'.             <--- Yes!
  yacc  main.y
  mv -f y.tab.c main.c
  Must remake target `main.bar'.
  cat main.c foo.h >main.bar || rm main.bar
  Successfully remade target file `main.bar'.
  Removing intermediate files...
  rm main.c

It looks like make -j2 swapped main.c and main.y


        I can't get around the fact that there is a reproducible
 difference based on whether or not the -j2 argument was give,

        manoj





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