niSwitch_UnlockSession
Specific Function
C Function Prototype
ViStatus niSwitch_UnlockSession (ViSession vi, ViBoolean* callerHasLock);
Purpose
This function releases a lock that you acquired on an instrument session using niSwitch_LockSession.
Refer to niSwitch_LockSession for additional information on session locks.
Parameters
| Name | Type | Description |
|---|---|---|
| vi | ViSession | A particular NI-SWITCH session established with niSwitch_InitWithTopology, niSwitch_InitWithOptions, or niSwitch_init and used for all subsequent NI-SWITCH calls. |
| callerHasLock | ViBoolean | This parameter serves as a convenience. If you do not want to use this parameter, pass VI_NULL. Use this parameter 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 niSwitch_LockSession or niSwitch_UnlockSession in the same function. The parameter is an input/output parameter. niSwitch_LockSession and niSwitch_UnlockSession each inspect the current value and take the following actions: - If the value is VI_TRUE, niSwitch_LockSession does not lock the session again. If the value is VI_FALSE, niSwitch_LockSession obtains the lock and sets the value of the parameter to VI_TRUE. - If the value is VI_FALSE, niSwitch_UnlockSession does not attempt to unlock the session. If the value is VI_TRUE, niSwitch_UnlockSession releases the lock and sets the value of the parameter to VI_FALSE. Thus, you can, call niSwitch_UnlockSession at the end of your function without worrying about whether you actually have the lock. Example: ViStatus TestFunc (ViSession vi, ViInt32 flags) { ViStatus error = VI_SUCCESS; ViBoolean haveLock = VI_FALSE; if (flags & BIT_1) { viCheckErr( niSwitch_LockSession(vi, &haveLock)); viCheckErr( TakeAction1(vi)); if (flags & BIT_2) { viCheckErr( niSwitch_UnlockSession(vi, &haveLock)); viCheckErr( TakeAction2(vi)); viCheckErr( niSwitch_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. */ niSwitch_UnlockSession(vi, &haveLock); return error; } |