Locking interfaces.

svn path=/trunk/; revision=6589

1 files changed, 404 insertions, 0 deletions

diff --git a/camel/camel-lock.c b/camel/camel-lock.c
new file mode 100644
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--- /dev/null
+++ b/camel/camel-lock.c
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+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*-
+ *
+ * Author: Michael Zucchi <notzed@helixcode.com>
+ *
+ * Copyright (C) 1999 Helix Code (http://www.helixcode.com/).
+ *
+ * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+
+#include <config.h>
+
+/* need configure checks here */
+#define USE_DOT
+#define USE_FCNTL
+#define USE_FLOCK
+
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <alloca.h>
+#include <string.h>
+
+#ifdef USE_DOT
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#endif
+
+#ifdef USE_FCNTL
+#include <unistd.h>
+#include <fcntl.h>
+#endif
+
+#ifdef USE_FLOCK
+#include <sys/file.h>
+#endif
+
+#include "camel-lock.h"
+
+/* dunno where this fucking thing is got from */
+/*#define _(x) (x)*/
+
+#define d(x) (printf("%s(%d): ", __FILE__, __LINE__),(x))
+
+/**
+ * camel_lock_dot:
+ * @path: 
+ * @ex: 
+ * 
+ * Create an exclusive lock using .lock semantics.
+ * All locks are equivalent to write locks (exclusive).
+ * 
+ * Return value: -1 on error, sets @ex appropriately.
+ **/
+int
+camel_lock_dot(const char *path, CamelException *ex)
+{
+#ifdef USE_DOT
+	char *locktmp, *lock;
+	int retry = 0;
+	int fdtmp, fd;
+	struct stat st;
+
+	/* TODO: Is there a reliable way to refresh the lock, if we're still busy with it?
+	   Does it matter?  We will normally also use fcntl too ... */
+
+	/* use alloca, save cleaning up afterwards */
+	lock = alloca(strlen(path) + strlen(".lock") + 1);
+	sprintf(lock, "%s.lock", path);
+	locktmp = alloca(strlen(path) + strlen("XXXXXX") + 1);
+
+#ifndef HAVE_MKSTEMP
+	sprintf(locktmp, "%sXXXXXX", path);
+	if (mktemp(locktmp) == NULL) {
+		/* well, this is really only a programatic error */
+		camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Could not create lock file for %s: %s"), path, strerror(errno));
+		return -1;
+	}
+#endif
+
+	while (retry < CAMEL_LOCK_DOT_RETRY) {
+
+		d(printf("trying to lock '%s', attempt %d\n", lock, retry));
+
+		if (retry > 0)
+			sleep(CAMEL_LOCK_DOT_DELAY);
+
+#ifdef HAVE_MKSTEMP
+		sprintf(locktmp, "%sXXXXXX", path);
+		fdtmp = mkstemp(locktmp);
+#else
+		fdtmp = open(locktmp, O_RDWR|O_CREAT|O_EXCL, 0600);
+#endif
+		if (fdtmp == -1) {
+			camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Could not create lock file for %s: %s"), path, strerror(errno));
+			return -1;
+		}
+		close(fdtmp);
+
+		/* apparently return code from link can be unreliable for nfs (see link(2)), so we ignore it */
+		link(locktmp, lock);
+
+		/* but we check stat instead (again, see link(2)) */
+		if (stat(locktmp, &st) == -1) {
+			d(printf("Out lock file %s vanished!?\n", locktmp));
+
+			/* well that was unexpected, try cleanup/retry */
+			unlink(locktmp);
+			unlink(lock);
+		} else {
+			d(printf("tmp lock created, link count is %d\n", st.st_nlink));
+
+			unlink(locktmp);
+
+			/* if we had 2 links, we have created the .lock, return ok, otherwise we need to keep trying */
+			if (st.st_nlink == 2)
+				return 0;
+		}
+
+		/* check for stale lock, kill it */
+		if (stat(lock, &st) == 0) {
+			time_t now = time(0);
+			d(printf("There is an existing lock %d seconds old\n", now-st.st_ctime));
+			if (st.st_ctime < now - CAMEL_LOCK_DOT_STALE) {
+				d(printf("Removing it now\n"));
+				unlink(lock);
+			}
+		}
+
+		retry++;
+	}
+
+	d(printf("failed to get lock after %d retries\n", retry));
+
+	camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Timed out trying to get lock file on %s. Try again later."), path);
+	return -1;
+#else /* ! USE_DOT */
+	return 0;
+#endif
+}
+
+/**
+ * camel_unlock_dot:
+ * @path: 
+ * 
+ * Attempt to unlock a .lock lock.
+ **/
+void
+camel_unlock_dot(const char *path)
+{
+#ifdef USE_DOT
+	char *lock;
+
+	lock = alloca(strlen(path) + strlen(".lock") + 1);
+	sprintf(lock, "%s.lock", path);
+	d(printf("unlocking %s\n", lock));
+	(void)unlink(lock);
+#endif
+}
+
+/**
+ * camel_lock_fcntl:
+ * @fd: 
+ * @type: 
+ * @ex: 
+ * 
+ * Create a lock using fcntl(2).
+ *
+ * @type is CAMEL_LOCK_WRITE or CAMEL_LOCK_READ,
+ * to create exclusive or shared read locks
+ * 
+ * Return value: -1 on error.
+ **/
+int
+camel_lock_fcntl(int fd, CamelLockType type, CamelException *ex)
+{
+#ifdef USE_FCNTL
+	struct flock lock;
+
+	d(printf("fcntl locking %d\n", fd));
+
+	memset(&lock, 0, sizeof(lock));
+	lock.l_type = type==CAMEL_LOCK_READ?F_RDLCK:F_WRLCK;
+	if (fcntl(fd, F_SETLK, &lock) == -1) {
+		camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Failed to get lock using fcntl(2): %s"), strerror(errno));
+		return -1;
+	}
+#endif
+	return 0;
+}
+
+/**
+ * camel_unlock_fcntl:
+ * @fd: 
+ * 
+ * Unlock an fcntl lock.
+ **/
+void
+camel_unlock_fcntl(int fd)
+{
+#ifdef USE_FCNTL
+	struct flock lock;
+
+	d(printf("fcntl unlocking %d\n", fd));
+
+	memset(&lock, 0, sizeof(lock));
+	lock.l_type = F_UNLCK;
+	fcntl(fd, F_SETLK, &lock);
+#endif
+}
+
+/**
+ * camel_lock_flock:
+ * @fd: 
+ * @type: 
+ * @ex: 
+ * 
+ * Create a lock using flock(2).
+ * 
+ * @type is CAMEL_LOCK_WRITE or CAMEL_LOCK_READ,
+ * to create exclusive or shared read locks
+ *
+ * Return value: -1 on error.
+ **/
+int
+camel_lock_flock(int fd, CamelLockType type, CamelException *ex)
+{
+#ifdef USE_FLOCK
+	int op;
+
+	d(printf("flock locking %d\n", fd));
+
+	if (type == CAMEL_LOCK_READ)
+		op = LOCK_SH|LOCK_NB;
+	else
+		op = LOCK_EX|LOCK_NB;
+
+	if (flock(fd, op) == -1) {
+		camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Failed to get lock using flock(2): %s"), strerror(errno));
+		return -1;
+	}
+#endif
+	return 0;
+}
+
+/**
+ * camel_unlock_flock:
+ * @fd: 
+ * 
+ * Unlock an flock lock.
+ **/
+void
+camel_unlock_flock(int fd)
+{
+#ifdef USE_FLOCK
+	d(printf("flock unlocking %d\n", fd));
+
+	(void)flock(fd, LOCK_UN);
+#endif
+}
+
+/**
+ * camel_lock_folder:
+ * @path: Path to the file to lock (used for .locking only).
+ * @fd: Open file descriptor of the right type to lock.
+ * @type: Type of lock, CAMEL_LOCK_READ or CAMEL_LOCK_WRITE.
+ * @ex: 
+ * 
+ * Attempt to lock a folder, multiple attempts will be made using all
+ * locking strategies available.
+ * 
+ * Return value: -1 on error, @ex will describe the locking system that failed.
+ **/
+int
+camel_lock_folder(const char *path, int fd, CamelLockType type, CamelException *ex)
+{
+	int retry = 0;
+
+	while (retry < CAMEL_LOCK_RETRY) {
+		if (retry > 0)
+			sleep(CAMEL_LOCK_DELAY);
+
+		camel_exception_clear(ex);
+
+		if (camel_lock_fcntl(fd, type, ex) == 0) {
+			if (camel_lock_flock(fd, type, ex) == 0) {
+				if (camel_lock_dot(path, ex) == 0)
+					return 0;
+				camel_unlock_flock(fd);
+			}
+			camel_unlock_fcntl(fd);
+		}
+		retry++;
+	}
+
+	return -1;
+}
+
+/**
+ * camel_unlock_folder:
+ * @path: Filename of folder.
+ * @fd: Open descrptor on which locks were placed.
+ * 
+ * Free a lock on a folder.
+ **/
+void
+camel_unlock_folder(const char *path, int fd)
+{
+	camel_unlock_dot(path);
+	camel_unlock_flock(fd);
+	camel_unlock_fcntl(fd);
+}
+
+#if 0
+int main(int argc, char **argv)
+{
+	CamelException *ex;
+	int fd1, fd2;
+
+	ex = camel_exception_new();
+
+#if 0
+	if (camel_lock_dot("mylock", ex) == 0) {
+		if (camel_lock_dot("mylock", ex) == 0) {
+			printf("Got lock twice?\n");
+		} else {
+			printf("failed to get lock 2: %s\n", camel_exception_get_description(ex));
+		}
+		camel_unlock_dot("mylock");
+	} else {
+		printf("failed to get lock 1: %s\n", camel_exception_get_description(ex));
+	}
+
+	camel_exception_clear(ex);
+#endif
+
+	fd1 = open("mylock", O_RDWR);
+	fd2 = open("mylock", O_RDWR);
+
+	if (camel_lock_fcntl(fd1, CAMEL_LOCK_WRITE, ex) == 0) {
+		printf("got fcntl write lock once\n");
+		sleep(5);
+		if (camel_lock_fcntl(fd2, CAMEL_LOCK_WRITE, ex) == 0) {
+			printf("got fcntl write lock twice!\n");
+		} else {
+			printf("failed to get write lock: %s\n", camel_exception_get_description(ex));
+		}
+
+		camel_exception_clear(ex);
+
+		if (camel_lock_fcntl(fd2, CAMEL_LOCK_READ, ex) == 0) {
+			printf("got fcntl read lock as well?\n");
+			camel_unlock_fcntl(fd2);
+		} else {
+			printf("failed to get read lock: %s\n", camel_exception_get_description(ex));
+		}
+
+		camel_exception_clear(ex);
+		camel_unlock_fcntl(fd1);
+	} else {
+		printf("failed to get write lock at all: %s\n", camel_exception_get_description(ex));
+	}
+
+	if (camel_lock_fcntl(fd1, CAMEL_LOCK_READ, ex) == 0) {
+		printf("got fcntl read lock once\n");
+		sleep(5);
+		if (camel_lock_fcntl(fd2, CAMEL_LOCK_WRITE, ex) == 0) {
+			printf("got fcntl write lock too?!\n");
+		} else {
+			printf("failed to get write lock: %s\n", camel_exception_get_description(ex));
+		}
+
+		camel_exception_clear(ex);
+
+		if (camel_lock_fcntl(fd2, CAMEL_LOCK_READ, ex) == 0) {
+			printf("got fcntl read lock twice\n");
+			camel_unlock_fcntl(fd2);
+		} else {
+			printf("failed to get read lock: %s\n", camel_exception_get_description(ex));
+		}
+
+		camel_exception_clear(ex);
+		camel_unlock_fcntl(fd1);
+	}
+
+	close(fd1);
+	close(fd2);
+
+	return 0;
+}
+#endif