Name: boT120536 Date: 02/13/2001


java version "1.2.2"
Solaris VM (build Solaris_JDK_1.2.2_05, native threads, sunwjit)

Here's another take on the javac dependency problem.

I want to use javac for parallel make.
I could live without global dependencies *if* javac
weren't so naive about the way it writes output files.
Say we have classes A & B, both of which use C.
Run javac on A & B simultaneously.
A gets to C first, compiles and starts writing C.class
B discovers C.class exists, so loads it, but gets
premature EOF because A hasn't finished writing.

I can think of several ways to solve the problem:

1: write output to a uniqe temp-file name, when complete use
   atomic rename system call to give it the proper name.
   Virtue: simple
   Vice: multiple javacs might compile the same class, wasting CPU

2: use file locks
   Virtue: avoids wasting CPU as for #1
   Vice: not portable to all UNIXes or filesystem types.
   this is probably a minor concern though, since those
   that don't have file locks are few & far between

3: if a reading javac hits premature EOF, and file modtime
   is "recent", retry the read "N" times. (must define
   "recent" and "N" somehow)
   Virtue: simple, avoids wasting CPU, doesn't use locks.
   Vice: could run into trouble with clock-skew & races.
(Review ID: 116744)
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