stream_select Runs the equivalent of the select() system call on the given arrays of streams with a timeout specified by tv_sec and tv_usec &reftitle.description; intstream_select arrayread arraywrite arrayexcept inttv_sec inttv_usec0 The stream_select function accepts arrays of streams and waits for them to change status. Its operation is equivalent to that of the socket_select function except in that it acts on streams. &reftitle.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. When stream_select returns, the arrays read, write and except are modified to indicate which stream resource(s) actually changed status. You do not need to pass every array to stream_select. You can leave it out and use an empty array or &null; instead. Also do not forget that those arrays are passed by reference and will be modified after stream_select returns. tv_sec The tv_sec and tv_usec together form the timeout parameter, tv_sec specifies the number of seconds while tv_usec the number of microseconds. The timeout is an upper bound on the amount of time that stream_select will wait before it returns. If tv_sec and tv_usec 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 tv_sec 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). 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. tv_usec See tv_sec description. &reftitle.returnvalues; On success stream_select returns the number of stream resources contained in the modified arrays, which may be zero if the timeout expires before anything interesting happens. On error &false; is returned and a warning raised (this can happen if the system call is interrupted by an incoming signal). &reftitle.examples; This example checks to see if data has arrived for reading on either $stream1 or $stream2. Since the timeout value is 0 it will return immediately: 0) { /* At least on one of the streams something interesting happened */ } ?> ]]> &reftitle.notes; Due to a limitation in the current Zend Engine it is not possible to pass a constant modifier like &null; directly as a parameter to a function which expects this parameter to be passed by reference. Instead use a temporary variable or an expression with the leftmost member being a temporary variable: ]]> Be sure to use the === operator when checking for an error. Since the stream_select may return 0 the comparison with == would evaluate to &true;: ]]> If you read/write to a stream returned in the arrays be aware that they do not necessarily read/write the full amount of data you have requested. Be prepared to even only be able to read/write a single byte. Windows compatibility: stream_select used on a pipe returned from proc_open may cause data loss under Windows 98. Use of stream_select on file descriptors returned by proc_open will fail and return &false; under Windows. &reftitle.seealso; stream_set_blocking