21  Environment Variables

This chapter describes the OpenMP environment variables that specify the settings of the ICVs that affect the execution of OpenMP programs (see Chapter 2). The names of the environment variables must be upper case. Unless otherwise specified, the values assigned to the environment variables are case insensitive and may have leading and trailing white space. Modifications to the environment variables after the program has started, even if modified by the program itself, are ignored by the OpenMP implementation. However, the settings of some of the ICVs can be modified during the execution of the OpenMP program by the use of the appropriate directive clauses or OpenMP API routines.

The following examples demonstrate how the OpenMP environment variables can be set in different environments:

• csh-like shells:

 
setenv OMP_SCHEDULE "dynamic"
  

• bash-like shells:

 
export OMP_SCHEDULE="dynamic"
  

• Windows Command Line:

 
set OMP_SCHEDULE=dynamic
  

As defined following Section 2.2 in Section 2.2, device-specific environment variables extend many of the environment variables defined in this chapter. If the corresponding environment variable for a specific device number, including the host device, is set, then the setting for that environment variable is used to set the value of the associated ICV of the device with the corresponding device number. If the corresponding environment variable that includes the _DEV suffix but no device number is set, then the setting of that environment variable is used to set the value of the associated ICV of any non-host device for which the device-number-specific corresponding environment variable is not set. In all cases the setting of an environment variable for which a device number is specified takes precedence.

Restrictions

• Device-specific environment variables must not correspond to environment variables that initialize ICVs with global scope.