Overview of Firebird Client Library Thread-Safety

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.

Definition of “Thread-Safety”

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.

Thread-Safety Table

FB Version	OS	FB Architecture	Remote / Local	Thread-Safe?
1.0.3	Windows	SuperServer	Local	No
			Remote	Yes
		Classic	Local	No such config.
			Remote	No such config.
		Embedded	Local	No such config.
			Remote	No such config.
	Linux	SuperServer	Local	No such config.
			Remote	No
		Classic	Local	No
			Remote	No
1.5	Windows	SuperServer	Local	No
			Remote	Yes
		Classic	Local	No such config.
			Remote	Yes
		Embedded	Local	Yes
			Remote	No such config.
	Linux	SuperServer	Local	No such config.
			Remote	Yes
		Classic	Local	No
			Remote	No
2.0/2.1	Windows	SuperServer	Local	Yes
			Remote	Yes
		Classic	Local	Yes
			Remote	Yes
		Embedded	Local	Yes
			Remote	No such config.
	Linux	SuperServer	Local	No such config.
			Remote	Yes
		Classic	Local	No
			Remote	No

This document was written by David Rushby, with assistance from Dmitry Yemanov. Errors are attributable to Rushby rather than Yemanov.