php man page for stream_set_write_buffer

STREAM_SET_WRITE_BUFFER(3)						 1						STREAM_SET_WRITE_BUFFER(3)

stream_set_write_buffer - Sets write file buffering on the given stream

SYNOPSIS
       int stream_set_write_buffer (resource  $stream, int  $buffer)

DESCRIPTION
	Sets the buffering for write operations on the given $stream to $buffer bytes.

	Output	using  fwrite(3) is normally buffered at 8K. This means that if there are two processes wanting to write to the same output stream
       (a file), each is paused after 8K of data to allow the other to write.

PARAMETERS
	      o $stream
		- The file pointer.

	      o $buffer
		- The number of bytes to buffer. If $buffer is 0 then write operations are unbuffered. This ensures that all writes with fwrite(3)
		are completed before other processes are allowed to write to that output stream.

RETURN VALUES
	Returns 0 on success, or EOF if the request cannot be honored.

EXAMPLES
       Example #1

	      stream_set_write_buffer(3) example

	       The following example demonstrates how to use stream_set_write_buffer(3) to create an unbuffered stream.

	      <?php
	      $fp = fopen($file, "w");
	      if ($fp) {
		stream_set_write_buffer($fp, 0);
		fwrite($fp, $output);
		fclose($fp);
	      }
	      ?>

SEE ALSO 
fopen(3), fwrite(3).
PHP Documentation Group 												STREAM_SET_WRITE_BUFFER(3)