This parameter serves as a convenience. If you do not want to use this parameter, pass VI_NULL.

Pass the address of a local ViBoolean variable. In the declaration of the local variable, initialize it to VI_FALSE. Pass the address of the same local variable to any other calls you make to the niFgen_LockSession function or the niFgen_UnlockSession function in the same function.

The parameter is an input/output parameter. The niFgen_LockSession function and the niFgen_UnlockSession function each inspect the current value and take the following actions:

• If the value is VI_TRUE, the niFgen_LockSession function does not lock the session again. If the value is VI_FALSE, the niFgen_LockSession function obtains the lock and sets the value of the parameter to VI_TRUE.
• If the value is VI_FALSE, the niFgen_UnlockSession function does not attempt to unlock the session. If the value is VI_TRUE, the niFgen_UnlockSession function releases the lock and sets the value of the parameter to VI_FALSE.

Thus, you can, call the niFgen_UnlockSession function at the end of your function without worrying about whether you actually have the lock.

Example:

ViStatus error = VI_SUCCESS;
ViBoolean haveLock = VI_FALSE;

if (flags & BIT_1)
{

viCheckErr(niFgen_LockSession(vi, &haveLock));
viCheckErr( TakeAction1(vi));
if (flags & BIT_2)
{

viCheckErr( niFgen_UnlockSession(vi, &haveLock));
viCheckErr( TakeAction2(vi));
viCheckErr( niFgen_LockSession(vi, &haveLock);

}
if (flags & BIT_3)

viCheckErr( TakeAction3(vi));

}

Error:

/*
At this point, you cannot really be sure that
you have the lock. Fortunately, the haveLock
variable takes care of that for you.
*/
niFgen_UnlockSession(vi, &haveLock);
return error;