Bug #79030 [Com]: $_SERVER['REQUEST_TIME_FLOAT'] and microtime(TRUE) combination problem

Edit report at https://bugs.php.net/bug.php?id=79030&edit=1 ID: 79030 Comment by: bugreports at gmail dot com Reported by: herbert at groot dot jebbink dot nl Summary: $_SERVER['REQUEST_TIME_FLOAT'] and microtime(TRUE) combination problem Status: Not a bug Type: Bug Package: *General Issues Operating System: ChromeOS / Crostini / Debian 10 PHP Version: 7.4.1 Block user comment: N Private report: N New Comment: > The SAPI is apache2handler, that one gives indeed msec als precision. > It seems usec is also available apache2handler on all of my setups is using usec this is a microtime(TRUE) based runtime measurement from a custom header 0.0245 / 0.0152 the first number is based on $_SERVER['REQUEST_TIME_FLOAT'] the second one is based on microtime(TRUE) as first codeline -------------------- $cms_stop_microtime = microtime(TRUE); $runtime_total = round(($cms_stop_microtime - $_SERVER['REQUEST_TIME_FLOAT']), 4); $tuntime_cms = round(($cms_stop_microtime - $cms_startup_microtime), 4); -------------------- this configures a additional http header which is also usec Header set "X-Response-Time" "%D us" X-Response-Time: D=25726 us Previous Comments: ------------------------------------------------------------------------ [2019-12-27 03:26:50] herbert at groot dot jebbink dot nl The SAPI is apache2handler, that one gives indeed msec als precision. https://github.com/php/php-src/blob/PHP-7.4.1/sapi/apache2handler/sapi_apache2.c#L360 It seems dat usec is also available http://apr.apache.org/docs/apr/1.5/group__apr__time.html ------------------------------------------------------------------------ [2019-12-26 08:23:26] requinix@php.net REQUEST_TIME_FLOAT is not rounded. To make sure, what SAPI are you using for the web side? One can define its own means of determining the request time, and if it does not then PHP falls back to gettimeofday. https://github.com/php/php-src/blob/PHP-7.4.1/main/SAPI.c#L1083 ------------------------------------------------------------------------ [2019-12-26 06:00:31] herbert at groot dot jebbink dot nl gettimeofday(2) may not be accurate at sub-millisecond level, but with 2 sequential calls the last one will not be lower then the first one. I think it is caused by the fact that $_SERVER['REQUEST_TIME_FLOAT'] is rounded to milliseconds and microtime(TRUE) is not. ------------------------------------------------------------------------ [2019-12-25 09:12:46] requinix@php.net Those two are backed by gettimeofday(2), which is not suitable for measuring time intervals to sub-millisecond precision. ------------------------------------------------------------------------ [2019-12-25 06:56:21] herbert at groot dot jebbink dot nl Description: ------------ Sometimes the $_SERVER['REQUEST_TIME_FLOAT'] and microtime(TRUE) combination gives strange results. Below example gives about 1 in 10 times a negative result. Test script: --------------- <?php $script1 = microtime(TRUE); $script2 = file_get_contents('http://localhost/script2.php'); echo $script2 - $script1; ?> <?php echo $_SERVER['REQUEST_TIME_FLOAT']; ?> Expected result: ---------------- 0.00038409233093262 Actual result: -------------- -0.00039100646972656 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=79030&edit=1