Find if the installed PHP is threadsafe or nonthreadsafe?

Open a phpinfo() and search for the line Thread safety. For a thread-safe build you should find enable.

As specified in the comments by Muhammad Gelbana you can also use:

• On Windows : php -i|findstr "Thread"
• On *nix: php -i|grep Thread

If you prefer to use the command line:

• *nix:

  php -i | grep -i "Thread"
  

• Windows:

  php -i | findstr -i "thread"
  

This should give you something like this:

Thread Safety => enabled

or

Thread Safety => disabled