util_time.c revision 35b9e4d5f3452cad4b3bec6829ce87a5ce9e9227
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2001-2002 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
* 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",
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*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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* ====================================================================
*
* 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
*
*/
#include "util_time.h"
/* Cache for exploded values of recent timestamps
*/
struct exploded_time_cache_element {
apr_int64_t t;
};
/* the "+ 1" is for the current second: */
struct exploded_time_cache_element *cache,
int use_gmt)
{
struct exploded_time_cache_element *cache_element =
/* 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_time_exp_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.
*/
sizeof(struct exploded_time_cache_element));
if ((seconds != cache_element_snapshot.t) ||
/* Invalid snapshot */
if (use_gmt) {
return apr_time_exp_gmt(xt, t);
}
else {
return apr_time_exp_lt(xt, t);
}
}
else {
/* Valid snapshot */
sizeof(apr_time_exp_t));
}
}
else {
apr_status_t r;
if (use_gmt) {
r = apr_time_exp_gmt(xt, t);
}
else {
r = apr_time_exp_lt(xt, t);
}
if (!APR_STATUS_IS_SUCCESS(r)) {
return r;
}
cache_element->t = seconds;
}
return APR_SUCCESS;
}
apr_time_t t)
{
}
apr_time_t t)
{
}
{
/* ### This code is a clone of apr_ctime(), except that it
* uses ap_explode_recent_localtime() instead of apr_time_exp_lt().
*/
const char *s;
int real_year;
/* example: "Wed Jun 30 21:49:08 1993" */
/* 123456789012345678901234 */
*date_str++ = *s++;
*date_str++ = *s++;
*date_str++ = *s++;
*date_str++ = ' ';
*date_str++ = *s++;
*date_str++ = *s++;
*date_str++ = *s++;
*date_str++ = ' ';
*date_str++ = ' ';
*date_str++ = ':';
*date_str++ = ':';
*date_str++ = ' ';
*date_str++ = 0;
return APR_SUCCESS;
}