Re: Compiling multiple sources at once

[Paul D. Smith]

%% Ray Ontko <address@hidden> writes:

  ro> The basic problem is this: It's much faster to compile many java
  ro> (or c) programs at once than it is to compile each separately.

For Java, I believe it.  For C, I doubt the speed increase is all that
great; some compilers won't even let you build multiple .o's with one
invocation of the compiler.

  ro> What I want to do is compile all files that are out of date at
  ro> once.

  ro> My Makefile looks something like this:

  ro> %.class : %.java
  ro>   javac $@

  ro> JAVA_FILES = a.java b.java c.java

  ro> CLASS_FILES = $(JAVA_FILES:.java=.class)

  ro> all : $(CLASS_FILES)

  ro> What happens:

  ro>   javac a.java
  ro>   javac b.java
  ro>   javac c.java

  ro> What I want to have happen:

  ro>   javac a.java b.java c.java

  ro> When I do a "make all", I want the a _single_ javac command to be 
  ro> executed, but only for those .class files which are out of date
  ro> with respect to their .java files.  It takes about 10 times as
  ro> long to do a separate javac for each file as it does to do a 
  ro> javac for all files.

  ro> Has anyone got a clever solution that allows multiple targets to
  ro> be coallesced into a single implicit rule?  Are there other
  ro> work-arounds?

There is no direct support in make for this.

You can hack it, but you cannot use implicit rules.  You'll have to do
something like this:

  JAVA_FILES = a.java b.java c.java

  all : .built_java_classes

  .built_java_classes : $(JAVA_FILES)
        javac $?
        @touch $@

-- 
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 Paul D. Smith <address@hidden>          Find some GNU make tips at:
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