Streams as Resources
All streams are registered as resources when they are created. This ensures
that they will be properly cleaned up even if there is some fatal error.
All of the filesystem functions in PHP operate on streams resources - that
means that your extensions can accept regular PHP file pointers as
parameters to, and return streams from their functions.
The streams API makes this process as painless as possible:
Example 43-2. How to accept a stream as a parameter
if (FAILURE == zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "r", &zstream))
/* you can now use the stream. However, you do not "own" the
stream, the script does. That means you MUST NOT close the
stream, because it will cause PHP to crash! */
Example 43-3. How to return a stream from a function
stream = php_stream_open_wrapper("http://www.php.net", "rb", REPORT_ERRORS, NULL);
/* after this point, the stream is "owned" by the script.
If you close it now, you will crash PHP! */
Since streams are automatically cleaned up, it's tempting to think that we can get
away with being sloppy programmers and not bother to close the streams when we
are done with them. Although such an approach might work, it is not a good idea
for a number of reasons: streams hold locks on system resources while they are
open, so leaving a file open after you have finished with it could prevent other
processes from accessing it. If a script deals with a large number of files,
the accumulation of the resources used, both in terms of memory and the
sheer number of open files, can cause web server requests to fail. Sounds
bad, doesn't it? The streams API includes some magic that helps you to
keep your code clean - if a stream is not closed by your code when it should
be, you will find some helpful debugging information in you web server error
Always use a debug build of PHP when developing an extension
(--enable-debug when running configure), as a lot of
effort has been made to warn you about memory and stream leaks.
In some cases, it is useful to keep a stream open for the duration of a request,
to act as a log or trace file for example. Writing the code to safely clean up
such a stream is not difficult, but it's several lines of code that are not
strictly needed. To save yourself the trouble of writing the code, you
can mark a stream as being OK for auto cleanup. What this means is
that the streams API will not emit a warning when it is time to auto-cleanup
a stream. To do this, you can use php_stream_auto_cleanup().