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From Daniel Spiewak <>
Subject Native Kernel#system on JRuby
Date Fri, 17 Apr 2009 18:42:31 GMT
I think we should consider this:

The reason being that JRuby's Kernel#system method is fundamentally broken
(because it is based on java.lang.Runtime.exec).  They've managed to piece
things together so that it's rarely an issue, but problems do surface when
doing things like the following:

system 'scala'

If you run this from JRuby, your terminal will freeze and refuse to accept
any input (except for escape sequences like Ctrl+C).  This limitation in
Kernel#system basically prevents any sort of working REPL support (git:// / interactive-shell).  In order to get
around this, I propose that Buildr should rewrite the Kernel#system
method *when
running under JRuby* so that it uses the platform's native `system` function
(from the C stdlib).  The commit linked above (51280ab) contains the
necessary implementation.  Note that this commit is basically untested, but
it seems to work on Mac for everything I've tried so far.

Advantages: Buildr's external process dispatch on JRuby will be more
predictable and basically in line with what happens on MRI.  This will
probably resolve/avoid some bugs and certainly opens up a whole new series
of possibilities (like the interactive shell support).

Disadvantages: It introduces a new gem dependency on JRuby (ffi-0.3.2) and
actually overwrites a core Ruby method.  It's the latter that has me the
most concerned.  Kernel#system is quite foundational to Buildr and Ruby in
general, so casually monkey-patching in a new implementation is not a step
which should be taken lightly.



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