Overview of Firebird Client Library Thread-Safety

Last updated 2005.11.20 20:21 EST

The thread-safety properties of the standard Firebird client library vary according to the following:

• Firebird version
• operating system
• Firebird server architecture (SuperServer, Classic, Embedded)
• underlying connection protocol (embedded vs. local vs. IPC vs. remote)

Determining whether the client library you're using is thread-safe can be quite confusing. This document aims to reduce that confusion by defining what thread-safety means in the context of the Firebird client library, then presenting a table that specifies which client library configurations are thread-safe.

Note that this document deals only with the standard Firebird client library that underlies the Firebird C API. It has no relevance to the clean-slate reimplementations in access libraries such as Jaybird.

Currently, the highest level of concurrency supported by any version of the Firebird client library is "thread-safety at the connection level".

When we say that the Firebird client library is "thread-safe at the connection level", we mean that it is safe to use a particular connection in only one thread at a time, although the same connection can be manipulated by different threads in a serial fashion, and different connections can be manipulated by different threads in parallel.

For example, in a multithreaded application server, it is safe for a particular connection to be leased from a connection pool by Thread A, used, and returned to the pool for later lease by Thread B. It is not safe for Thread A and Thread B to use the same connection at the same time.

This document was written by David Rushby, with assistance from Dmitry Yemanov. Errors are attributable to Rushby rather than Yemanov, and should be reported by e-mail to woodsplitter@rocketmail.com.