Since PHPC-912, php_phongo_pclient_destroy (called during MSHUTDOWN) allows libmongoc clients created by parent processes to leak rather than call mongoc_client_destroy on them. That issue was released in 1.2.6 and was a necessary work-around to ensure that destroying a libmongoc client within a child process did not affect sockets created by parent processes; however, that CDRIVER-2049 (released in libmongoc 1.7.0) formally addressed that by adding pid-tracking to libmongoc's socket structs. Since then, socket fds are merely closed rather than shutdown.

PHPC-1274 adds additional logic to reset libmongoc clients (CDRIVER-2857) created by parent processes, which will avoid a child killing sessions and cursors. This reset behavior has no effect on sockets (per CDRIVER-3116).

We should investigate whether it's possible to remove the behavior in PHPC-912 and always destroy clients during MSHUTDOWN, after conditionally freeing the client if it was created by a parent process.

One outstanding question is whether there might still be adverse effects for SSL connections as described in CDRIVER-3116, despite the socket pid-tracking from CDRIVER-2049. If there is any chance that the child process could disturb a parent's SSL connections, we should leave the current behavior as-is.