Bug #80234 Client library fails to close handle on mutex used by shared memory connections

• Submitted: 2 Feb 2016 11:58
• Modified: 15 Feb 2016 17:42
• Reporter: Daniel Blanchard
• Status: Closed
• Category: MySQL Server: C API (client library)
• Severity: S2 (Serious)
• Version: 5.7
• OS: Any
• CPU Architecture: Any

[2 Feb 2016 11:58] Daniel Blanchard

Description:
The Windows client library opens a handle on a mutex for shared memory connections but does not explicitly close it.

An attempt to restart the MySQL server (configured to use shared memory connections) will fail if a client process still has a handle open on the shared memory mutex as the server will fail to (re)create the mutex.

How to repeat:
1) Start MySQL server with shared memory connections enabled.
2) Connect to the server using a shared memory connection - e.g. use 
mysql.exe --protocol=memory -u root
3) Shut the server down whilst leaving the client running
4) Attempt to start the server again: Startup of server fails with error "Can't create shared memory service: Another instance of application already running.. : No such file or directory"

Suggested fix:
Call CloseHandle(connect_named_mutex) and set connect_named_mutex = NULL in the create_shared_memory function in sql-common\client.c after the ReleaseMutex(connect_named_mutex) call and in the err: code block.

[15 Feb 2016 17:42] Paul DuBois

Noted in 5.7.12, 5.8.0 changelogs.

For shared-memory connections on Windows, the client library opened a
handle on a mutex but did not close it. Subsequent attempts to
restart the server on the other end of the connection failed if the
client still had the mutex handle open.