pipeutils: Add utils for pipe signals

Add pipeutils.c with utility functions for working with pipes as
signals across threads. Using pipes for signals makes it easy for
the main thread to wait on (multiple) file descriptors with or
without a timeout.

src/Makefile.am

@@ -14,6 +14,7 @@ redshift_SOURCES = \
 	gamma-dummy.c gamma-dummy.h \
 	hooks.c hooks.h \
 	location-manual.c location-manual.h \
+	pipeutils.c pipeutils.h \
 	redshift.c redshift.h \
 	signals.c signals.h \
 	solar.c solar.h \

src/pipeutils.c

@@ -0,0 +1,98 @@
+/* pipeutils.c -- Utilities for using pipes as signals
+   This file is part of Redshift.
+
+   Redshift 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 3 of the License, or
+   (at your option) any later version.
+
+   Redshift 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 Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2017  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+
+#ifndef _WIN32
+
+/* Create non-blocking set of pipe fds. */
+int
+pipeutils_create_nonblocking(int pipefds[2])
+{
+	int r = pipe(pipefds);
+	if (r == -1) {
+		perror("pipe");
+		return -1;
+	}
+
+	int flags = fcntl(pipefds[0], F_GETFL);
+	if (flags == -1) {
+		perror("fcntl");
+		close(pipefds[0]);
+		close(pipefds[1]);
+		return -1;
+	}
+
+	r = fcntl(pipefds[0], F_SETFL, flags | O_NONBLOCK);
+	if (r == -1) {
+		perror("fcntl");
+		close(pipefds[0]);
+		close(pipefds[1]);
+		return -1;
+	}
+
+	flags = fcntl(pipefds[1], F_GETFL);
+	if (flags == -1) {
+		perror("fcntl");
+		close(pipefds[0]);
+		close(pipefds[1]);
+		return -1;
+	}
+
+	r = fcntl(pipefds[1], F_SETFL, flags | O_NONBLOCK);
+	if (r == -1) {
+		perror("fcntl");
+		close(pipefds[0]);
+		close(pipefds[1]);
+		return -1;
+	}
+
+	return 0;
+}
+
+#else /* _WIN32 */
+
+/* Create non-blocking set of pipe fds.
+
+   Not supported on Windows! Always fails. */
+int
+pipeutils_create_nonblocking(int pipefds[2])
+{
+	return -1;
+}
+
+#endif
+
+/* Signal on write-end of pipe. */
+void
+pipeutils_signal(int write_fd)
+{
+	write(write_fd, "", 1);
+}
+
+/* Mark signal as handled on read-end of pipe. */
+void
+pipeutils_handle_signal(int read_fd)
+{
+	char data;
+	read(read_fd, &data, 1);
+}

src/pipeutils.h

@@ -0,0 +1,28 @@
+/* pipeutils.h -- Utilities for using pipes as signals
+   This file is part of Redshift.
+
+   Redshift 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 3 of the License, or
+   (at your option) any later version.
+
+   Redshift 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 Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2017  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+#ifndef REDSHIFT_PIPEUTILS_H
+#define REDSHIFT_PIPEUTILS_H
+
+int pipeutils_create_nonblocking(int pipefds[2]);
+
+void pipeutils_signal(int write_fd);
+void pipeutils_handle_signal(int read_fd);
+
+#endif /* ! REDSHIFT_PIPEUTILS_H */