You need to measure time with finer than one-second resolution—for example, to generate a unique ID or benchmark a function call.
Use microtime(true) to get the current time in seconds and microseconds. Example 3-24 uses microtime(true) to time how long it takes to do 1,000 regular expression matches.
Example 3-24. Timing with microtime()
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$start = microtime(true); for ($i = 0; $i < 1000; $i++) { preg_match('/age=\d{1,5}/',$_SERVER['QUERY_STRING']); } $end = microtime(true); $elapsed = $end - $start; |
Without an argument that evaluates to true, microtime() returns a string that contains the microseconds part of elapsed time since the epoch, a space, and seconds since the epoch.
For example, a return value of 0.41644100 1026683258 means that 1026683258.41644100 seconds have elapsed since the epoch.
This allows for more precision than can fit into a float, but makes it difficult to calculate with.
Since PHP 5.4.0, the $_SERVER superglobal array is populated with a RE QUEST_TIME_FLOAT entry. This contains the time (including microseconds) when the request started.
This makes it easy to determine how long a request has been running at any point—just compute microtime(true) – $_SERVER[‘REQUEST_TIME_FLOAT’].
Time including microseconds is useful for generating unique IDs. When combined with the current process ID, it guarantees a unique ID, as long as a process doesn’t generate more than one ID per microsecond.
Example 3-25 uses microtime() (with its string return format) to generate just such an ID.
Example 3-25. Generating an ID with microtime()
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list($microseconds,$seconds) = explode(' ',microtime()); $id = $seconds.$microseconds.getmypid(); |
Note that the method in Example 3-25 is not as foolproof on multithreaded systems, where there is a nonzero (but very tiny) chance that two threads of the same process could call microtime() during the same microsecond.
