add --daemon option to serve command. for issue 45.

code looks odd because it is portable to windows. windows does not have
os.fork, so have to spawn and use pipe to tell parent ready instead.

doc/hg.1.txt

@@ -543,10 +543,12 b' serve [options]::'
 
     options:
     -A, --accesslog <file>   name of access log file to write to
+    -d, --daemon             run server in background, as a daemon
     -E, --errorlog <file>    name of error log file to write to
     -a, --address <addr>     address to use
     -p, --port <n>           port to use (default: 8000)
     -n, --name <name>        name to show in web pages (default: working dir)
+    --pid-file <file>        write server process ID to given file
     -t, --templatedir <path> web templates to use
     -6, --ipv6               use IPv6 in addition to IPv4
 

mercurial/commands.py

@@ -2022,6 +2022,16 b' def serve(ui, repo, **opts):'
         if opts[o]:
             ui.setconfig("web", o, opts[o])
 
+    if opts['daemon'] and not opts['daemon_pipefd']:
+        rfd, wfd = os.pipe()
+        args = sys.argv[:]
+        args.append('--daemon-pipefd=' + str(wfd))
+        pid = os.spawnvp(os.P_NOWAIT | getattr(os, 'P_DETACH', 0),
+                         args[0], args)
+        os.close(wfd)
+        os.read(rfd, 1)
+        os._exit(0)
+
     try:
         httpd = hgweb.create_server(repo)
     except socket.error, inst:
@@ -2040,6 +2050,24 b' def serve(ui, repo, **opts):'
             ui.status(_('listening at http://%s:%d/\n') % (addr, port))
         else:
             ui.status(_('listening at http://%s/\n') % addr)
+
+    if opts['pid_file']:
+        fp = open(opts['pid_file'], 'w')
+        fp.write(str(os.getpid()))
+        fp.close()
+
+    if opts['daemon_pipefd']:
+        wfd = int(opts['daemon_pipefd'])
+        os.write(wfd, 'y')
+        os.close(wfd)
+        sys.stdout.flush()
+        sys.stderr.flush()
+        fd = os.open(util.nulldev, os.O_RDWR)
+        if fd != 0: os.dup2(fd, 0)
+        if fd != 1: os.dup2(fd, 1)
+        if fd != 2: os.dup2(fd, 2)
+        if fd not in (0, 1, 2): os.close(fd)
+
     httpd.serve_forever()
 
 def status(ui, repo, *pats, **opts):
@@ -2476,11 +2504,14 b' table = {'
     "^serve":
         (serve,
          [('A', 'accesslog', '', _('name of access log file to write to')),
+          ('d', 'daemon', None, _('run server in background')),
+          ('', 'daemon-pipefd', '', ''),
           ('E', 'errorlog', '', _('name of error log file to write to')),
           ('p', 'port', 0, _('port to use (default: 8000)')),
           ('a', 'address', '', _('address to use')),
           ('n', 'name', '',
            _('name to show in web pages (default: working dir)')),
+          ('', 'pid-file', '', _('name of file to write process ID to')),
           ('', 'stdio', None, _('for remote clients')),
           ('t', 'templates', '', _('web templates to use')),
           ('', 'style', '', _('template style to use')),