forgot to checkin select.c

(This used to be commit 719bc2f130393a55058f5c45ca6fbd30a78de2dc)

1 files changed, 107 insertions, 0 deletions

diff --git a/source3/lib/select.c b/source3/lib/select.c
new file mode 100644
index 0000000000..cd77d1209f
--- /dev/null
+++ b/source3/lib/select.c
@@ -0,0 +1,107 @@
+/* 
+   Unix SMB/Netbios implementation.
+   Version 3.0
+   Samba select/poll implementation
+   Copyright (C) Andrew Tridgell 1992-1998
+   
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include "includes.h"
+
+/* this is here because it allows us to avoid a nasty race in signal handling. 
+   We need to guarantee that when we get a signal we get out of a select immediately
+   but doing that involves a race condition. We can avoid the race by getting the 
+   signal handler to write to a pipe that is in the select/poll list 
+
+   this means all Samba signal handlers should call sys_select_signal()
+*/
+static int initialised;
+static int select_pipe[2];
+static unsigned pipe_written, pipe_read;
+
+
+/*******************************************************************
+call this from all Samba signal handlers if you want to avoid a 
+nasty signal race condition
+********************************************************************/
+void sys_select_signal(void)
+{
+	char c = 1;
+	if (!initialised) return;
+
+	if (pipe_written > pipe_read+256) return;
+
+	if (write(select_pipe[1], &c, 1) == 1) pipe_written++;
+}
+
+/*******************************************************************
+like select() but avoids the signal race using a pipe
+it also guuarantees that fds on return only ever contains bits set
+for file descriptors that were readable
+********************************************************************/
+int sys_select(int maxfd, fd_set *fds,struct timeval *tval)
+{
+	int ret;
+
+	if (!initialised) {
+		initialised = 1;
+		pipe(select_pipe);
+	}
+
+	maxfd = MAX(select_pipe[0], maxfd);
+	FD_SET(select_pipe[0], fds);
+	errno = 0;
+	ret = select(maxfd,fds,NULL,NULL,tval);
+
+	if (ret <= 0) {
+		FD_ZERO(fds);
+	}
+
+	if (FD_ISSET(select_pipe[0], fds)) {
+		FD_CLR(select_pipe[0], fds);
+		ret--;
+		if (ret == 0) {
+			ret = -1;
+			errno = EINTR;
+		}
+	}
+
+	while (pipe_written != pipe_read) {
+		char c;
+		if (read(select_pipe[0], &c, 1) == 1) pipe_read++;
+	}
+
+	return ret;
+}
+
+/*******************************************************************
+similar to sys_select() but catch EINTR and continue
+this is what sys_select() used to do in Samba
+********************************************************************/
+int sys_select_intr(int maxfd, fd_set *fds,struct timeval *tval)
+{
+	int ret;
+	fd_set fds2;
+
+	do {
+		fds2 = *fds;
+		ret = sys_select(maxfd, &fds2, tval);
+	} while (ret == -1 && errno == EINTR);
+
+	*fds = fds2;
+
+	return ret;
+}