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stream_select

Description

The stream_select of Stream for PHP runs the equivalent of the select() system call on the given arrays of streams with a timeout specified by seconds and microseconds.

Syntax

stream_select(
    ?array &$read,
    ?array &$write,
    ?array &$except,
    ?int $seconds,
    ?int $microseconds = null
): int|false

Parameters

read

The streams listed in the read array will be watched to see if characters become available for reading (more precisely, to see if a read will not block - in particular, a stream resource is also ready on end-of-file, in which case an fread() will return a zero length string).

write

The streams listed in the write array will be watched to see if a write will not block.

except

The streams listed in the except array will be watched for high priority exceptional ("out-of-band") data arriving.

NOTE: When stream_select() returns, the arrays read, write and except are modified to indicate which stream resource(s) actually changed status.

seconds

The seconds and microseconds together form the timeout parameter, seconds specifies the number of seconds while microseconds the number of microseconds. The timeout is an upper bound on the amount of time that stream_select() will wait before it returns. If seconds and microseconds are both set to 0, stream_select() will not wait for data - instead it will return immediately, indicating the current status of the streams.

If seconds is null stream_select() can block indefinitely, returning only when an event on one of the watched streams occurs (or if a signal interrupts the system call).

WARNING: Using a timeout value of 0 allows you to instantaneously poll the status of the streams, however, it is NOT a good idea to use a 0 timeout value in a loop as it will cause your script to consume too much CPU time. It is much better to specify a timeout value of a few seconds, although if you need to be checking and running other code concurrently, using a timeout value of at least 200000 microseconds will help reduce the CPU usage of your script. Remember that the timeout value is the maximum time that will elapse; stream_select() will return as soon as the requested streams are ready for use.

microseconds

See seconds description.

Return

Returns the number of stream resources contained in the modified arrays on success, which may be zero if the timeout expires before anything interesting happens, or false and a warning on error (this can happen if the system call is interrupted by an incoming signal).

Examples

1 · read write except seconds

<?

$filename = "https://osbo.com";
$mode = "r";

$handle1 = fopen($filename, $mode);
$handle2 = fopen($filename, $mode);

    $read = [$handle1, $handle2];
    $write = null;
    $except = null;
    $seconds = 0;

    $return = stream_select($read, $write, $except, $seconds);

    var_export($return);

fclose($handle2);
fclose($handle1);

2 · microseconds
<?

$filename = "https://osbo.com";
$mode = "r";

$handle1 = fopen($filename, $mode);
$handle2 = fopen($filename, $mode);

    $read = [$handle1, $handle2];
    $write = null;
    $except = null;
    $seconds = 0;
    $microseconds = 200000;

    $return = stream_select($read, $write, $except, $seconds, $microseconds);

    var_export($return);

fclose($handle2);
fclose($handle1);