EvIo and polling backends unable to use php://memory or php://temp

[Mark K]

On linux, the default backend is EVBACKEND_EPOLL. Both epoll and regular poll cannot handle php:// file streams.

With epoll we get Bad File Descriptor errors

With poll we get Inappropriate ioctl for device errors.

<?php
//works fine with select backend, comment this line to see problem
$defaultLoop =  EvLoop::defaultLoop(Ev::BACKEND_SELECT);

//comment out select and try poll backend
//$defaultLoop =  EvLoop::defaultLoop(Ev::BACKEND_POLL);

//php://memory and php://temp fail with polling backends
$pathToTest = 'php://temp';

//try a regular file
//$pathToTest = '/tmp/foo';

$f = fopen($pathToTest, 'r+');

// Wait until STDIN is readable
$w = new EvIo($f, Ev::READ, function ($watcher, $revents) use ($pathToTest) { 
    echo "$pathToTest is readable\n";
});


//on Linux should dump 4 EPOLL
if (Ev::backend() == Ev::BACKEND_EPOLL || Ev::backend() == Ev::BACKEND_POLL) { 
    echo "using (e)poll backend, warnings about file descriptors...\n";
}

Ev::run(Ev::RUN_ONCE | Ev::RUN_NOWAIT);
usleep(1000);
Ev::run(Ev::RUN_ONCE | Ev::RUN_NOWAIT);
usleep(1000);
Ev::run(Ev::RUN_ONCE | Ev::RUN_NOWAIT);

[Mark K]

This might just need a documentation point about poll backends not working with not real FD.

[Ruslan Osmanov]

The memory based streams have no associated file descriptors, so we can not listen to read/write events there.

This is how data is written to memory stream: https://github.com/php/php-src/blob/PHP-5.6/main/streams/memory.c#L100 . Just plain memcpy(). Well, the "php://temp" stream wrapper implements a cast to STDIO, but it is done by flushing the data to file, which is not what you probably want: https://github.com/php/php-src/blob/PHP-5.6/main/streams/memory.c#L475

EvIo::__construct() and EvIo::set() from now on will throw exception in case of memory based stream. Plus warnings replaced with exceptions.

Actually, the Linux kernel(version 3.17 and above) allows to create a file in RAM with memfd_create() syscall. However, PHP doesn't support this feature yet.

We might introduce a new stream as well. I don't feel like bloating the ext. with custom streams, though.

Probably, the simplest solution now is to create a regular file in tmpfs.

[Mark K]

Yes, warning or exception is fine. Thank you.