Many posix functions give very useful information in the errno code when an error occurs. For instance, stream_select(), when it generates an error, according to the man page (man 2 select) may return one of four different errors which are listed as: EBADF, EINTR, EINVAL, ENOMEM. See the man page for more specific information about these. In this example, when the stream_select() function returns false, posix_get_last_error() will return a non-zero value that will be set to one of these constants. For instance, if stream_select() == false, and posix_get_last_error() == EBADF, then one of the file descriptors given to the select() function has probably closed somehow. If, on the other hand, posix_get_last_error() returns EINTR then stream_select() returned FALSE not because of any true error condition, but only because the process handled a signal. When the signal arrives while stream_select() is blocking it will always stop blocking and return false immediately. This behavior makes sense, though it can seem inconvenient. You just have to handle it correctly. (not many do, in php.)
From this example it should probably be clear that one should at least consider handling different error types in different ways. EINTER should probably be ignored for instance, unless your program uses signalling to open or close file handles or sockets.
These error constants listed in the related POSIX man pages are not part of the PHP interface. When you call posix_get_last_error() it will return an integer. The problem with getting an unnamed integer return code is that these integers may mean different things on different systems. You can (and probably should) pass the resulting integer to the posix_strerror() function, which will return an accurate human-readable description of what the error is. This is useful of course, but mainly for logging. (String descriptions of errors are far more prone to change than are the actual integer value codes.) Truly, when using the result of posix_errno() it is best to check the value against a set of possible constants. The constants you compare them to are system specific, as stated earlier, so you need to look them up on that system. Here is an easy and reliable way to do that.
Look at the errno man page ($ man errno) and copy all of the constant names into a very basic C file. like this.
===================================
#include <errno.h>
#include <stdio.h>
int main(){
printf("define('E2BIG', %d);\n", E2BIG);
printf("define('EACCES', %d);\n", EACCES);
printf("define('EADDRINUSE', %d);\n", EADDRINUSE);
printf("define('EADDRNOTAVAIL', %d);\n", EADDRNOTAVAIL);
// ... etc. etc.
}
===================================
Now, if you just run this code through the C pre-processor (i.e. 'gcc -E cfile.c'), then those constant names will be replaced by the numbers which are used on your system. (warning: running the C compiler/pre-processor needs to take place on the system where the PHP code will be running. keep track of whether nfs is in use or something else along those lines which may separate your coding environment from the runtime environment.) In addition to running the C pre-processor you also simply compile and run the above program (i.e. 'gcc cfile.c && ./a.out'). Running it will generate a PHP compatible list of define() calls that will correctly define these constants in your PHP program on the target system, so will be usable. Simply copy the definitions into a php file.
To finish the example, you might use these constants like this:
$selret = stream_select( $r, $w, $e, $to );
if( $selret === false )
{
switch( posix_get_last_error() )
{
case EBADF: /* one of the handles is bad. fix it. */ break;
case EINVAL: /* $to is negative? woops. */ break;
case ENOMEM:
throw new exception("probable memory leak. restart.");
break;
case EINTR:
break; // usually ignore EINTR after select() is fine.
}
}
