Move actual work out of the SIGCHLD signal handler for the dart:io

Move actual work out of the SIGCHLD signal handler for the dart:io
process library.

Use the self-pipe trick to signal a dedicated thread when a SIGCHLD
signal is received. The dedicated thread will perform the actual work
of extracting the exit code and posting it back to Dart.

R=sgjesse@google.com
BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=3711

[Søren Gjesse, 2012-01-31 08:19:18]

LGTM!

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
File runtime/bin/process_linux.cc (right):

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
runtime/bin/process_linux.cc:40: // Singly-linked list of ProcessInfo objects
for all active processes
We could consider changing this list to a hash map.

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
runtime/bin/process_linux.cc:187: ssize_t read_bytes =
FDUtils::ReadFromBlocking(pollfds.fd, &data, 1);
Should there be a way to gracefully shutdown this thread, e.g writing 255?

In main we could then have a call to ExitCodeHandler::Shutdown().

[Mads Ager (google), 2012-01-31 08:37:47]

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
File runtime/bin/process_linux.cc (right):

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
runtime/bin/process_linux.cc:40: // Singly-linked list of ProcessInfo objects
for all active processes
On 2012/01/31 08:19:18, Søren Gjesse wrote:
> We could consider changing this list to a hash map.

Agreed, we could. This is so simple that I would like to keep it for now. Let's
see if we can make these methods show up on a profile. :-)

https://chromiumcodereview.appspot.com/9293030/diff/2001/runtime/bin/process_...
runtime/bin/process_linux.cc:187: ssize_t read_bytes =
FDUtils::ReadFromBlocking(pollfds.fd, &data, 1);
On 2012/01/31 08:19:18, Søren Gjesse wrote:
> Should there be a way to gracefully shutdown this thread, e.g writing 255?
> 
> In main we could then have a call to ExitCodeHandler::Shutdown().

As discussed offline, we need to do this both for this new thread and for the
event-handler thread on isolate shutdown. Let me look into that in a separate
changelist.