(PECL eio >= 0.0.1dev)
eio_open — Opens a file
$path
   , int $flags
   , int $mode
   , int $pri
   , callable $callback
   [, mixed $data = NULL
  ] )
  eio_open() opens file specified by
  path in access mode mode with
  
pathPath of the file to be opened.
In some SAPIs(e.g. PHP-FPM) it could fail, if you don't specify full path.
flagsOne of EIO_O_* constants, or their
    combinations. EIO_O_* constants have the same
    meaning, as their corresponding O_* counterparts
    defined in fnctl.h C header file. Default is
    EIO_O_RDWR.
    
modeOne of EIO_S_I* constants, or their combination (via bitwise OR operator). The constants have the same meaning as their S_I* counterparts defined in » sys/stat.h C header file. Required, if a file is created. Otherwise ignored.
priThe request priority: EIO_PRI_DEFAULT, EIO_PRI_MIN, EIO_PRI_MAX, or NULL.
If NULL passed, pri internally is set to
EIO_PRI_DEFAULT.
callback
callback function is called when the request is done.
It should match the following prototype: 
void callback(mixed $data, int $result[, resource $req]);
datais custom data passed to the request.
resultrequest-specific result value; basically, the value returned by corresponding system call.
reqis optional request resource which can be used with functions like eio_get_last_error()
data
      Arbitrary variable passed to callback.
     
   eio_open() returns file descriptor in
   result argument of callback
   on success; otherwise, result is equal to -1.
  
Example #1 eio_open() example
<?php
$temp_filename = "eio-temp-file.tmp";
/* Is called when eio_close() finishes */
function my_close_cb($data, $result) {
 // Zero indicates success
    var_dump($result == 0);
 @unlink($data);
}
/* Is called when eio_open() finishes */
function my_file_opened_callback($data, $result) {
 // $result should contain the file descriptor
    var_dump($result > 0);
    if ($result > 0) {
  // Close the file
        eio_close($result, EIO_PRI_DEFAULT, "my_close_cb", $data);
        eio_event_loop();
    }
}
// Create new file for reading and writing
// Deny group and others to do anything with that file
eio_open($temp_filename, EIO_O_CREAT | EIO_O_RDWR, EIO_S_IRUSR | EIO_S_IWUSR,
  EIO_PRI_DEFAULT, "my_file_opened_callback", $temp_filename);
eio_event_loop();
?>
The above example will output something similar to:
bool(true) bool(true)