Closing PDO descriptors for child processes

Description

At least on Unix systems, whenever PHP creates a child process, whether through conventional means like shell_exec(), passthru(), or proc_open(), or through stuff like pcntl_fork(), the child process inherits all of the open file descriptors, including any open authenticated PDO database connections.

This is generally not desirable. Even in contexts where it's not a security concern, two processes should not share one connection to a database because the first one to use it will mess it up for the other one.

In other languages, this is avoided by calling something like:

fcntl( fd, F_SETFD, F_CLOEXEC );

on the database's file handle. But PHP doesn't provide this functionality (that I'm aware of) without exotic extensions and even if it did, there's no way (that I'm aware of) to get at the system file descriptor corresponding to a PDO connection.

Would it be possible/reasonable to add something to PDO::setAttribute() that would, when invoked, set that flag on the underlying descriptor where it is applicable?

Start with PDO::setAttribute() and the Unix process paths named in the issue: shell_exec(), passthru(), proc_open(), and pcntl_fork(). Determine how PDO connections expose or inherit descriptors and define coverage for the requested behavior; done when the supported setting prevents inheritance where applicable.