Threads considerations

 

A user-defined function (UDF) that is defined as FENCED runs in the same job as the SQL statement that calls the function. However, the UDF runs in a system thread, separate from the thread that is running the SQL statement.

Because the UDF runs in the same job as the SQL statement, it shares much of the same environment as the SQL statement. However, because it runs under a separate thread, the following threads considerations apply:

• The UDF will conflict with thread level resources held by the SQL statement's thread. Primarily, these are the table resources discussed above.

• UDFs do not inherit any program adopted authority that may have been active at the time the SQL statement was called. UDF authority comes from either the authority associated with the UDF program itself or the authority of the user running the SQL statement.

• The UDF cannot perform any operation that is blocked from being run in a secondary thread.

• The UDF program must be created such that it either runs under a named activation group or in the activation group of its caller (ACTGRP parameter). Programs that specify ACTGRP(*NEW) will not be allowed to run as UDFs.

 

Parent topic:

Writing UDFs as external functions

 

Related reference

Multithreaded applications
Fenced or unfenced considerations