--- /dev/null
+/* ====================================================================
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2001 The Apache Software Foundation. All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * 3. The end-user documentation included with the redistribution,
+ * if any, must include the following acknowledgment:
+ * "This product includes software developed by the
+ * Apache Software Foundation (http://www.apache.org/)."
+ * Alternately, this acknowledgment may appear in the software itself,
+ * if and wherever such third-party acknowledgments normally appear.
+ *
+ * 4. The names "Apache" and "Apache Software Foundation" must
+ * not be used to endorse or promote products derived from this
+ * software without prior written permission. For written
+ * permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache",
+ * nor may "Apache" appear in their name, without prior written
+ * permission of the Apache Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation. For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+#ifndef APACHE_UTIL_TIME_H
+#define APACHE_UTIL_TIME_H
+
+#include "apr.h"
+#include "apr_time.h"
+#include "httpd.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @package Apache date/time handling functions
+ */
+
+/* Maximum delta from the current time, in seconds, for a past time
+ * to qualify as "recent" for use in the ap_explode_recent_*() functions:
+ */
+#define AP_TIME_RECENT_THRESHOLD 15
+
+/**
+ * convert a recent time to its human readable components in local timezone
+ * @param tm the exploded time
+ * @param t the time to explode: MUST be within the last
+ * AP_TIME_RECENT_THRESHOLD seconds
+ * @note This is a faster alternative to apr_explode_localtime that uses
+ * a cache of pre-exploded time structures. It is useful for things
+ * that need to explode the current time multiple times per second,
+ * like loggers.
+ * @return APR_SUCCESS iff successful
+ * @deffunc apr_status_t ap_explode_recent_localtime(apr_exploded_time_t *tm, apr_time_t t);
+ */
+AP_DECLARE(apr_status_t) ap_explode_recent_localtime(apr_exploded_time_t *tm,
+ apr_time_t t);
+
+/**
+ * convert a recent time to its human readable components in GMT timezone
+ * @param tm the exploded time
+ * @param t the time to explode: MUST be within the last
+ * AP_TIME_RECENT_THRESHOLD seconds
+ * @note This is a faster alternative to apr_explode_gmt that uses
+ * a cache of pre-exploded time structures. It is useful for things
+ * that need to explode the current time multiple times per second,
+ * like loggers.
+ * @return APR_SUCCESS iff successful
+ * @deffunc apr_status_t ap_explode_recent_gmt(apr_exploded_time_t *tm, apr_time_t t);
+ */
+AP_DECLARE(apr_status_t) ap_explode_recent_gmt(apr_exploded_time_t *tm,
+ apr_time_t t);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !APACHE_UTIL_TIME_H */
--- /dev/null
+/* ====================================================================
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2001 The Apache Software Foundation. All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * 3. The end-user documentation included with the redistribution,
+ * if any, must include the following acknowledgment:
+ * "This product includes software developed by the
+ * Apache Software Foundation (http://www.apache.org/)."
+ * Alternately, this acknowledgment may appear in the software itself,
+ * if and wherever such third-party acknowledgments normally appear.
+ *
+ * 4. The names "Apache" and "Apache Software Foundation" must
+ * not be used to endorse or promote products derived from this
+ * software without prior written permission. For written
+ * permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache",
+ * nor may "Apache" appear in their name, without prior written
+ * permission of the Apache Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation. For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+#include "util_time.h"
+
+/* Cache for exploded values of recent timestamps
+ */
+
+struct exploded_time_cache_element {
+ apr_int64_t t;
+ apr_exploded_time_t xt;
+ apr_int64_t t_validate; /* please see comments in cached_explode() */
+};
+
+/* the "+ 1" is for the current second: */
+#define TIME_CACHE_SIZE (AP_TIME_RECENT_THRESHOLD + 1)
+
+static struct exploded_time_cache_element exploded_cache_localtime[TIME_CACHE_SIZE];
+static struct exploded_time_cache_element exploded_cache_gmt[TIME_CACHE_SIZE];
+
+
+static apr_status_t cached_explode(apr_exploded_time_t *xt, apr_time_t t,
+ struct exploded_time_cache_element *cache,
+ int use_gmt)
+{
+ apr_int64_t seconds = t / APR_USEC_PER_SEC;
+ struct exploded_time_cache_element *cache_element =
+ &(cache[seconds % TIME_CACHE_SIZE]);
+ struct exploded_time_cache_element cache_element_snapshot;
+
+ /* The cache is implemented as a ring buffer. Each second,
+ * it uses a different element in the buffer. The timestamp
+ * in the element indicates whether the element contains the
+ * exploded time for the current second (vs the time
+ * 'now - AP_TIME_RECENT_THRESHOLD' seconds ago). If the
+ * cached value is for the current time, we use it. Otherwise,
+ * we compute the apr_exploded_time_t and store it in this
+ * cache element. Note that the timestamp in the cache
+ * element is updated only after the exploded time. Thus
+ * if two threads hit this cache element simultaneously
+ * at the start of a new second, they'll both explode the
+ * time and store it. I.e., the writers will collide, but
+ * they'll be writing the same value.
+ */
+ if (cache_element->t >= seconds) {
+ /* There is an intentional race condition in this design:
+ * in a multithreaded app, one thread might be reading
+ * from this cache_element to resolve a timestamp from
+ * TIME_CACHE_SIZE seconds ago at the same time that
+ * another thread is copying the exploded form of the
+ * current time into the same cache_element. (I.e., the
+ * first thread might hit this element of the ring buffer
+ * just as the element is being recycled.) This can
+ * also happen at the start of a new second, if a
+ * reader accesses the cache_element after a writer
+ * has updated cache_element.t but before the writer
+ * has finished updating the whole cache_element.
+ *
+ * Rather than trying to prevent this race condition
+ * with locks, we allow it to happen and then detect
+ * and correct it. The detection works like this:
+ * Step 1: Take a "snapshot" of the cache element by
+ * copying it into a temporary buffer.
+ * Step 2: Check whether the snapshot contains consistent
+ * data: the timestamps at the start and end of
+ * the cache_element should both match the 'seconds'
+ * value that we computed from the input time.
+ * If these three don't match, then the snapshot
+ * shows the cache_element in the middle of an
+ * update, and its contents are invalid.
+ * Step 3: If the snapshot is valid, use it. Otherwise,
+ * just give up on the cache and explode the
+ * input time.
+ */
+ memcpy(&cache_element_snapshot, cache_element,
+ sizeof(struct exploded_time_cache_element));
+ if ((seconds != cache_element_snapshot.t) ||
+ (seconds != cache_element_snapshot.t_validate)) {
+ /* Invalid snapshot */
+ if (use_gmt) {
+ return apr_explode_gmt(xt, t);
+ }
+ else {
+ return apr_explode_localtime(xt, t);
+ }
+ }
+ else {
+ /* Valid snapshot */
+ memcpy(xt, &(cache_element_snapshot.xt),
+ sizeof(apr_exploded_time_t));
+ }
+ }
+ else {
+ apr_status_t r;
+ if (use_gmt) {
+ r = apr_explode_gmt(xt, t);
+ }
+ else {
+ r = apr_explode_localtime(xt, t);
+ }
+ if (!APR_STATUS_IS_SUCCESS(r)) {
+ return r;
+ }
+ cache_element->t = seconds;
+ memcpy(&(cache_element->xt), xt, sizeof(apr_exploded_time_t));
+ cache_element->t_validate = seconds;
+ }
+ xt->tm_usec = t % APR_USEC_PER_SEC;
+ return APR_SUCCESS;
+}
+
+
+AP_DECLARE(apr_status_t) ap_explode_recent_localtime(apr_exploded_time_t * tm,
+ apr_time_t t)
+{
+ return cached_explode(tm, t, exploded_cache_localtime, 0);
+}
+
+AP_DECLARE(apr_status_t) ap_explode_recent_gmt(apr_exploded_time_t * tm,
+ apr_time_t t)
+{
+ return cached_explode(tm, t, exploded_cache_gmt, 1);
+}
projects / thirdparty / apache / httpd.git / commitdiff
