niDCPower_UnlockSession

ViStatus niDCPower_UnlockSession(ViSession vi, ViBoolean *callerHasLock)

Purpose

Releases a lock that you acquired on an device session using niDCPower_LockSession. Refer to niDCPower_LockSession for additional information on session locks.

Parameters

Input
Name	Type	Description
vi	ViSession	Identifies a particular instrument session. vi is obtained from the niDCPower_init or niDCPower_InitWithOptions function.
Output
Name	Type	Description
callerHasLock	ViBoolean*	this attribute is optional. If you do not want to use this attribute, pass VI_NULL. Use this attribute in complex functions to keep track of whether you obtain a lock and therefore need to unlock the session. 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 niDCPower_LockSession or niDCPower_UnlockSessionin the same function. The parameter is an input/output parameter. niDCPower_LockSession and niDCPower_UnlockSessioneach inspect the current value and take the following actions. If the value is VI_TRUE, niDCPower_LockSession does not lock the session again. If the value is VI_FALSE, niDCPower_LockSession obtains the lock and sets the value of the parameter to VI_TRUE. If the value is VI_FALSE, niDCPower_UnlockSessiondoes not attempt to unlock the session. If the value is VI_TRUE, niDCPower_UnlockSessionreleases the lock and sets the value of the parameter to VI_FALSE. Thus, you can, call niDCPower_UnlockSession at the end of your function without worrying about whether you actually have the lock, as the following example shows. ViStatus TestFunc (ViSession vi, ViInt32 flags) { ViStatus error = VI_SUCCESS; ViBoolean haveLock = VI_FALSE; if (flags & BIT_1) { viCheckErr( niDCPower_LockSession(vi, &haveLock)); viCheckErr( TakeAction1(vi)); if (flags & BIT_2) { viCheckErr( niDCPower_UnlockSession(vi, &haveLock)); viCheckErr( TakeAction2(vi)); viCheckErr( niDCPower_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.*/ niDCPower_UnlockSession(vi, &haveLock); return error; }

Return Value

Name	Type	Description
Status	ViStatus	Reports the status of this operation. To obtain a text description of the status code, call the niDCPower_error_message function. To obtain additional information concerning the error condition, call the niDCPower_GetError function.