Set blocking/non-blocking mode on a stream
(PHP 4 >= 4.3.0, PHP 5)
Code Examples / Notes » stream_set_blocking
When you use fwrite() on a non-blocking stream, data isn't discarded silently as t dot starling said.
Remember that fwrite() returns an int, and this int represents the amount of data really written to the stream. So, if you see that fwrite() returns less than the amount of written data, it means you'll have to call fwrite() again in the future to write the remaining amount of data.
You can use stream_select() to wait for the stream to be available for writing, then continue writing data to the stream.
Non-blocking streams are useful as you can have more than one non-blocking stream, and wait for them to be available for writing.
t dot starling
Warning: if you write too much data to a stream in non-blocking mode and fill the buffer, the excess will be silently discarded. Observed in PHP 4.4.0 under linux.
Please notice that this function will not work as for PHP 5.2.0 at least on Win32 systems. It probably won't work on Linux boxes either.
PHP just ignores the function and blocking remains active.
For more information take a look at Bug #36918.
A concise description of Blocking vs. Non-blocking:
5.2.1 Blocking behavior in simple-streams
There are three modes of blocking behavior when writing
items in a sequence to a stream or filling a sequence with items read from a stream. The issue is what to do when (for writing) the entire sequence cannot be written and (for reading) the entire sequence cannot be filled, but no EOF is encountered. (By `the entire sequence', we mean that part specified by start and end if those are supplied.) Here are the modes and a description of what happens in that mode if the whole operation does not complete and no EOF is encountered.
1. Blocking mode: the system blocks (waits or hangs) until the operation can be completed.
2. Blocking/Non-Blocking (B/NB) mode: the system only blocks on the first element of the sequence: if it cannot be written or read, the system blocks. If the first element is successfully written or read, and a subsequent element cannot be written or read, the function doing the writing/reading returns, typically with the return value(s) indicating exactly what was accomplished.
3. Non-Blocking mode: the system never blocks. If an element cannot be written or read, the function doing the writing/reading returns, typically with the return value(s) indicating exactly what was accomplished.