CL commands and thread safety

The Integrated Language Environment^® (ILE) CL run time and compiler-generated code are threadsafe. Original program model (OPM) CL programs are not threadsafe.

For any ILE CL code that is compiled before Version 4 Release 3 or any OPM CL code, the CL run time sends a CPD000B diagnostic message and continues to run with unpredictable results. This might or might not be threadsafe, depending on the underlying code.

Command analyzer is threadsafe. For a given command, if the threadsafe attribute (THDSAFE) is *NO and the multithreaded job action attribute (MLTTHDACN) is set to *NORUN or *MSG, the command analyzer does one of the following when such a command is called in a job capable of multithreaded operations:

If MLTTHDACN is set to *NORUN in a multithreaded job, command analyzer sends a CPD000D diagnostic message, and the command does not run. A CPF0001 escape message then follows the CPD000D diagnostic message.
If MLTTHDACN is set to *MSG in a multithreaded job, command analyzer sends a CPD000D diagnostic message, and the program continues to run with unpredictable results.
If the job is capable of running multiple threads but is not actually multithreaded, command analyzer allows commands that are not threadsafe to run without interference.

If MLTTHDACN is set to *RUN, the command analyzer does not send a diagnostic message and allows the command to run. The results of this are unpredictable. Also, MLTTHDACN only applies to comments whose THDSAFE value is *NO. To determine the THDSAFE and MLTTHDACN values for a command, use Display Command (DSPCMD).

The MLTTHDACN value of some commands is set to *SYSVAL. In this case, command analyzer uses the QMLTTHDACN system value to decide how to process the command.

To display the setting of this value on i5/OS™:

DSPSYSVAL SYSVAL(QMLTTHDACN)

To change the setting of this value on i5/OS:

CHGSYSVAL SYSVAL(QMLTTHDACN) VALUE(x)

Sample output from DSPSYSVAL:

 Display System Value 

 System value . . . . . : QMLTTHDACN 
 Description . . . . . : Multithreaded job action 


 Multithreaded job 
 action . . . . . . . : 2 
 1=Perform the function that is not 
 threadsafe without sending a message 
 2=Perform the function that is not 
 threadsafe and send an informational 
 message 
 3=Do not perform the function that is 
 not threadsafe