We've been facing an issue with PHPMailer (PHPMailer/PHPMailer#3183) where stream_select() returns false, but because our application uses setlocale(LC_ALL, 'de_DE.UTF-8'), the PHP warning does NOT contain the string 'interrupted system call' which results in unexpected behavior (no retry happening).

We did found a fix for this: PHPMailer/PHPMailer#3193

I received a great hint by @teefax – who pointed out that the stream_select(): Unable to select part of the php warning message is not translated for other locales. Only the interrupted system call part is translated.

That Unable to select is followed by an error number in square brackets. However that number can be different based on the operating system of the server. But PHP has a constant SOCKET_EINTR for that.

So the recommendation is to check for the SOCKET_EINTR constant which is defined under Windows and UNIX-like platforms (if available on the platform) and use that with the other english warning text to catch those interrupted system calls for non-english locale applications.

I left the existing check to avoid any potential unknown breaking change and extended the if-condition.

As I known Symfony was using a similar approach, I'm recommending to apply this enhancement to the "interrupted check" as well.