Add jwack, a GNU make-like jobserver.

Theoretically compatible with GNU make's jobserver pipes.  Haven't tested
that yet.

jwack.py

@@ -0,0 +1,145 @@
+#!/usr/bin/python
+#
+# beware the jobberwack
+#
+import sys, os, errno, select, subprocess, fcntl
+import options
+from helpers import *
+
+optspec = """
+jwack [-j maxjobs] -- <command...>
+--
+j,jobs=    maximum jobs to run at once
+"""
+
+_fds = None
+_tokens = {}
+_waitfds = {}
+
+
+def setup(maxjobs):
+    global _fds
+    if _fds:
+        return  # already set up
+    flags = ' ' + os.getenv('MAKEFLAGS', '') + ' '
+    FIND = ' --jobserver-fds='
+    ofs = flags.find(FIND)
+    if ofs >= 0:
+        s = flags[ofs+len(FIND):]
+        (arg,junk) = s.split(' ', 1)
+        (a,b) = arg.split(',', 1)
+        a = atoi(a)
+        b = atoi(b)
+        if a <= 0 or b <= 0:
+            raise ValueError('invalid --jobserver-fds: %r' % arg)
+        _fds = (a,b)
+    if maxjobs and not _fds:
+        # need to start a new server
+        _fds = os.pipe()
+        os.write(_fds[1], 't' * maxjobs)
+        os.putenv('MAKEFLAGS',
+                  '%s --jobserver-fds=%d,%d -j ' % (os.getenv('MAKEFLAGS'),
+                                                    _fds[0], _fds[1]))
+
+
+def wait(want_token):
+    rfds = _waitfds.keys()
+    if _fds and want_token:
+        rfds.append(_fds[0])
+    r,w,x = select.select(rfds, [], [])
+    #print 'readable: %r' % r
+    for fd in r:
+        if _fds and fd == _fds[0]:
+            pass
+        else:
+            p = _waitfds[fd]
+            os.write(_fds[1], 't' * _tokens[fd])
+            b = os.read(fd, 1)
+            #print 'read: %r' % b
+            if b:
+                #print 'giving up %d tokens for child' % _tokens[fd]
+                _tokens[fd] = 0
+            else:
+                os.close(fd)
+                del _waitfds[fd]
+                del _tokens[fd]
+                p.wait()
+
+
+def wait_for_token():
+    pfd = atoi(os.getenv('JWACK_PARENT_FD', ''))
+    #print 'pfd is %d' % pfd
+    if pfd:
+        #print 'wrote to pfd'
+        os.write(pfd, 'j')  # tell parent to give back his token
+    while 1:
+        print 'waiting for tokens...'
+        wait(want_token=1)
+        if _fds:
+            fcntl.fcntl(_fds[0], fcntl.F_SETFL, os.O_NONBLOCK)
+            try:
+                b = os.read(_fds[0], 1)  # FIXME try: block
+            except OSError, e:
+                if e.errno == errno.EAGAIN:
+                    b = ''
+                    pass
+                else:
+                    raise
+            if b:
+                break
+    print 'got a token.'
+
+
+def wait_all():
+    while _waitfds:
+        wait(want_token=0)
+
+
+def force_return_tokens():
+    n = sum(_tokens.values())
+    print 'returning %d tokens' % n
+    if _fds:
+        os.write(_fds[1], 't' * n)
+        for k in _tokens.keys():
+            _tokens[k] = 0
+
+
+def _pre_job(r,w):
+    os.putenv('JWACK_PARENT_FD', str(w))
+    os.close(r)
+    
+
+def start_job(argv, stdout=None):
+    global _mytokens
+    setup(1)
+    if stdout:
+        argx = dict(stdout=stdout)
+    else:
+        argx = dict()
+    wait_for_token()
+    r,w = os.pipe()
+    p = subprocess.Popen(argv, preexec_fn=lambda: _pre_job(r,w), **argx)
+    os.close(w)
+    _waitfds[r] = p
+    _tokens[r] = 1
+    return p
+    
+
+def main():
+    o = options.Options('jwack', optspec)
+    (opt, flags, extra) = o.parse(sys.argv[1:])
+
+    if not extra:
+        o.fatal("no command line given")
+
+    setup(opt.jobs)
+    try:
+        p = start_job(extra)
+        wait_all()
+        return p.wait()
+    finally:
+        force_return_tokens()
+
+
+if __name__ == "__main__":
+    sys.exit(main())