/* Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "util_time.h" /* Cache for exploded values of recent timestamps */ struct exploded_time_cache_element { apr_int64_t t; apr_time_exp_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) /* Note that AP_TIME_RECENT_THRESHOLD is defined to * be a power of two minus one in util_time.h, so that * we can replace a modulo operation with a bitwise AND * when hashing items into a cache of size * AP_TIME_RECENT_THRESHOLD+1 */ #define TIME_CACHE_MASK (AP_TIME_RECENT_THRESHOLD) 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_time_exp_t *xt, apr_time_t t, struct exploded_time_cache_element *cache, int use_gmt) { apr_int64_t seconds = apr_time_sec(t); struct exploded_time_cache_element *cache_element = &(cache[seconds & TIME_CACHE_MASK]); 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_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. */ 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_time_exp_gmt(xt, t); } else { return apr_time_exp_lt(xt, t); } } else { /* Valid snapshot */ memcpy(xt, &(cache_element_snapshot.xt), 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 (r != APR_SUCCESS) { return r; } cache_element->t = seconds; memcpy(&(cache_element->xt), xt, sizeof(apr_time_exp_t)); cache_element->t_validate = seconds; } xt->tm_usec = (int)apr_time_usec(t); return APR_SUCCESS; } AP_DECLARE(apr_status_t) ap_explode_recent_localtime(apr_time_exp_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_time_exp_t * tm, apr_time_t t) { return cached_explode(tm, t, exploded_cache_gmt, 1); } AP_DECLARE(apr_status_t) ap_recent_ctime(char *date_str, 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(). */ apr_time_exp_t xt; const char *s; int real_year; /* example: "Wed Jun 30 21:49:08 1993" */ /* 123456789012345678901234 */ ap_explode_recent_localtime(&xt, t); s = &apr_day_snames[xt.tm_wday][0]; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = ' '; s = &apr_month_snames[xt.tm_mon][0]; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = ' '; *date_str++ = xt.tm_mday / 10 + '0'; *date_str++ = xt.tm_mday % 10 + '0'; *date_str++ = ' '; *date_str++ = xt.tm_hour / 10 + '0'; *date_str++ = xt.tm_hour % 10 + '0'; *date_str++ = ':'; *date_str++ = xt.tm_min / 10 + '0'; *date_str++ = xt.tm_min % 10 + '0'; *date_str++ = ':'; *date_str++ = xt.tm_sec / 10 + '0'; *date_str++ = xt.tm_sec % 10 + '0'; *date_str++ = ' '; real_year = 1900 + xt.tm_year; *date_str++ = real_year / 1000 + '0'; *date_str++ = real_year % 1000 / 100 + '0'; *date_str++ = real_year % 100 / 10 + '0'; *date_str++ = real_year % 10 + '0'; *date_str++ = 0; return APR_SUCCESS; } AP_DECLARE(apr_status_t) ap_recent_rfc822_date(char *date_str, apr_time_t t) { /* ### This code is a clone of apr_rfc822_date(), except that it * uses ap_explode_recent_gmt() instead of apr_time_exp_gmt(). */ apr_time_exp_t xt; const char *s; int real_year; ap_explode_recent_gmt(&xt, t); /* example: "Sat, 08 Jan 2000 18:31:41 GMT" */ /* 12345678901234567890123456789 */ s = &apr_day_snames[xt.tm_wday][0]; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = ','; *date_str++ = ' '; *date_str++ = xt.tm_mday / 10 + '0'; *date_str++ = xt.tm_mday % 10 + '0'; *date_str++ = ' '; s = &apr_month_snames[xt.tm_mon][0]; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = *s++; *date_str++ = ' '; real_year = 1900 + xt.tm_year; /* This routine isn't y10k ready. */ *date_str++ = real_year / 1000 + '0'; *date_str++ = real_year % 1000 / 100 + '0'; *date_str++ = real_year % 100 / 10 + '0'; *date_str++ = real_year % 10 + '0'; *date_str++ = ' '; *date_str++ = xt.tm_hour / 10 + '0'; *date_str++ = xt.tm_hour % 10 + '0'; *date_str++ = ':'; *date_str++ = xt.tm_min / 10 + '0'; *date_str++ = xt.tm_min % 10 + '0'; *date_str++ = ':'; *date_str++ = xt.tm_sec / 10 + '0'; *date_str++ = xt.tm_sec % 10 + '0'; *date_str++ = ' '; *date_str++ = 'G'; *date_str++ = 'M'; *date_str++ = 'T'; *date_str++ = 0; return APR_SUCCESS; }
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