How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Question

For example, I have the following code: 
 bool interruptFlag;

void interruptHanler(void)
{
 interruptFlag = true;
}

void main(void)
{
 while (true)
 {
 if (interruptFlag)
 { interruptFlag = false;
 processThings(); // process heavier things here
 }
 // CRITICAL POINT: what if interrupt occurs here?
 sd_app_evt_wait();
 }
}
 
 What if the interrupt occurs after checking the flag, but just before entering sd_app_evt_wait()? Does the sd_app_evt_wait() then just block and the system eventually jams to wait for the next possible interrupt? 
 The question: If the above speculation is true, can I somehow disable interrupts in-between checking my software flag and entering the sd_app_evt_wait()? The code could then look something like: 
 sd_nvic_critical_region_enter(...);
while (interruptFlag) // loop again if interrupt occurs while processing previous
{ sd_nvic_critical_region_exit(...);
 interruptFlag = false;
 processThings();
 sd_nvic_critical_region_enter(...);
}
// Now we are inside critical region thus application interrupt cannot occur here.
sd_app_evt_wait(); // does this enable application interrupts automatically?
 
 So, can I enter sd_app_evt_wait() while inside critical region?

Susheel Nuguru · Accepted Answer

Hi Jarmo, 
 sd_app_evt_wait() calls wait in the sequence of
__WFE()
__SEV()
__WFE() 
 This way if the interrupt happened just before calling sd_app_evt_wait, then the above sequence will not sleep because 
__WFE() -> The internal event was set as an interrupt occured just before this , now the event is cleared and this _WFE does nothing, means it wont go to sleep 
 __SEV()-> Set the event register explicitly 
 __WFE-> since we set event register explicitly, this __WFE will also not do anything apart from clearing the event register. 
 The above sequence will also work perfectly if no interrupt happened before calling sd_app_evt_wait 
__WFE()-> since no internal event is set, this will make chip go to sleep (system idle) 
 __SEV -> executing this means the chip has woken up now or before in other context, we are setting internal event just to make sure 
 __WFE -> clear the internal event and do nothing, so now we are awake and all events handled and cleared. 
 sd_app_evt_wait also keeps track of application interrupts forwarded and acked by softdevice. So it avoids any race condition.

How to avoid interrupt handling is not missed with sd_app_evt_wait()?

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