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/* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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#include "util_time.h"
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/* Cache for exploded values of recent timestamps
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struct exploded_time_cache_element {
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apr_int64_t t_validate; /* please see comments in cached_explode() */
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/* the "+ 1" is for the current second: */
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#define TIME_CACHE_SIZE (AP_TIME_RECENT_THRESHOLD + 1)
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/* Note that AP_TIME_RECENT_THRESHOLD is defined to
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* be a power of two minus one in util_time.h, so that
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* we can replace a modulo operation with a bitwise AND
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* when hashing items into a cache of size
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* AP_TIME_RECENT_THRESHOLD+1
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#define TIME_CACHE_MASK (AP_TIME_RECENT_THRESHOLD)
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static struct exploded_time_cache_element exploded_cache_localtime[TIME_CACHE_SIZE];
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static struct exploded_time_cache_element exploded_cache_gmt[TIME_CACHE_SIZE];
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static apr_status_t cached_explode(apr_time_exp_t *xt, apr_time_t t,
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struct exploded_time_cache_element *cache,
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apr_int64_t seconds = apr_time_sec(t);
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struct exploded_time_cache_element *cache_element =
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&(cache[seconds & TIME_CACHE_MASK]);
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struct exploded_time_cache_element cache_element_snapshot;
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/* The cache is implemented as a ring buffer. Each second,
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* it uses a different element in the buffer. The timestamp
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* in the element indicates whether the element contains the
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* exploded time for the current second (vs the time
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* 'now - AP_TIME_RECENT_THRESHOLD' seconds ago). If the
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* cached value is for the current time, we use it. Otherwise,
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* we compute the apr_time_exp_t and store it in this
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* cache element. Note that the timestamp in the cache
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* element is updated only after the exploded time. Thus
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* if two threads hit this cache element simultaneously
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* at the start of a new second, they'll both explode the
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* time and store it. I.e., the writers will collide, but
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* they'll be writing the same value.
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if (cache_element->t >= seconds) {
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/* There is an intentional race condition in this design:
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* in a multithreaded app, one thread might be reading
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* from this cache_element to resolve a timestamp from
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* TIME_CACHE_SIZE seconds ago at the same time that
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* another thread is copying the exploded form of the
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* current time into the same cache_element. (I.e., the
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* first thread might hit this element of the ring buffer
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* just as the element is being recycled.) This can
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* also happen at the start of a new second, if a
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* reader accesses the cache_element after a writer
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* has updated cache_element.t but before the writer
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* has finished updating the whole cache_element.
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* Rather than trying to prevent this race condition
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* with locks, we allow it to happen and then detect
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* and correct it. The detection works like this:
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* Step 1: Take a "snapshot" of the cache element by
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* copying it into a temporary buffer.
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* Step 2: Check whether the snapshot contains consistent
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* data: the timestamps at the start and end of
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* the cache_element should both match the 'seconds'
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* value that we computed from the input time.
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* If these three don't match, then the snapshot
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* shows the cache_element in the middle of an
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* update, and its contents are invalid.
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* Step 3: If the snapshot is valid, use it. Otherwise,
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* just give up on the cache and explode the
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memcpy(&cache_element_snapshot, cache_element,
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sizeof(struct exploded_time_cache_element));
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if ((seconds != cache_element_snapshot.t) ||
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(seconds != cache_element_snapshot.t_validate)) {
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/* Invalid snapshot */
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return apr_time_exp_gmt(xt, t);
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return apr_time_exp_lt(xt, t);
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memcpy(xt, &(cache_element_snapshot.xt),
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sizeof(apr_time_exp_t));
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r = apr_time_exp_gmt(xt, t);
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r = apr_time_exp_lt(xt, t);
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if (r != APR_SUCCESS) {
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cache_element->t = seconds;
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memcpy(&(cache_element->xt), xt, sizeof(apr_time_exp_t));
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cache_element->t_validate = seconds;
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xt->tm_usec = (int)apr_time_usec(t);
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AP_DECLARE(apr_status_t) ap_explode_recent_localtime(apr_time_exp_t * tm,
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return cached_explode(tm, t, exploded_cache_localtime, 0);
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AP_DECLARE(apr_status_t) ap_explode_recent_gmt(apr_time_exp_t * tm,
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return cached_explode(tm, t, exploded_cache_gmt, 1);
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AP_DECLARE(apr_status_t) ap_recent_ctime(char *date_str, apr_time_t t)
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/* ### This code is a clone of apr_ctime(), except that it
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* uses ap_explode_recent_localtime() instead of apr_time_exp_lt().
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/* example: "Wed Jun 30 21:49:08 1993" */
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/* 123456789012345678901234 */
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ap_explode_recent_localtime(&xt, t);
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s = &apr_day_snames[xt.tm_wday][0];
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s = &apr_month_snames[xt.tm_mon][0];
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*date_str++ = xt.tm_mday / 10 + '0';
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*date_str++ = xt.tm_mday % 10 + '0';
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*date_str++ = xt.tm_hour / 10 + '0';
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*date_str++ = xt.tm_hour % 10 + '0';
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*date_str++ = xt.tm_min / 10 + '0';
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*date_str++ = xt.tm_min % 10 + '0';
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*date_str++ = xt.tm_sec / 10 + '0';
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*date_str++ = xt.tm_sec % 10 + '0';
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real_year = 1900 + xt.tm_year;
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*date_str++ = real_year / 1000 + '0';
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*date_str++ = real_year % 1000 / 100 + '0';
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*date_str++ = real_year % 100 / 10 + '0';
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*date_str++ = real_year % 10 + '0';
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AP_DECLARE(apr_status_t) ap_recent_rfc822_date(char *date_str, apr_time_t t)
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/* ### This code is a clone of apr_rfc822_date(), except that it
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* uses ap_explode_recent_gmt() instead of apr_time_exp_gmt().
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ap_explode_recent_gmt(&xt, t);
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/* example: "Sat, 08 Jan 2000 18:31:41 GMT" */
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/* 12345678901234567890123456789 */
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s = &apr_day_snames[xt.tm_wday][0];
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*date_str++ = xt.tm_mday / 10 + '0';
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*date_str++ = xt.tm_mday % 10 + '0';
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s = &apr_month_snames[xt.tm_mon][0];
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real_year = 1900 + xt.tm_year;
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/* This routine isn't y10k ready. */
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*date_str++ = real_year / 1000 + '0';
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*date_str++ = real_year % 1000 / 100 + '0';
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*date_str++ = real_year % 100 / 10 + '0';
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*date_str++ = real_year % 10 + '0';
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*date_str++ = xt.tm_hour / 10 + '0';
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*date_str++ = xt.tm_hour % 10 + '0';
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*date_str++ = xt.tm_min / 10 + '0';
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*date_str++ = xt.tm_min % 10 + '0';
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*date_str++ = xt.tm_sec / 10 + '0';
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*date_str++ = xt.tm_sec % 10 + '0';