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6 years, 6 months ago.
How to tell if an EventQueue is starved?
Great talk on Event Queues, sorry I missed the live feed.
One question that occurred to me, is there any mechanism or method to indicate if an EventQueue is being starved for execution?
The queue.call_every(1000, printf, "called every 1 seconds\n"); call within the example code of the EventQueue reference page got me thinking down this path.
Below is a scenario which would cause timing violation of the "call_every()" which would be useful to be able to detect or be aware of:
Example_EventQueue_Starvation
#include "mbed.h"
#include "mbed_events.h"
#include <stdio.h>
void main_action(){
// Do something that takes longer than desired call_every time...
wait(1.5); // something like this
printf("trying to call every 1 second\n");
}
int main() {
// creates a queue with the default size
EventQueue queue;
// events are simple callbacks
queue.call_every(1000, main_action);
// events are executed by the dispatch method
queue.dispatch();
}
Question relating to:
1 Answer
6 years, 6 months ago.
Hello Mark,
I think one method could be to measure the actual interval of event execution. For example as below:
#include "mbed.h"
#include "mbed_events.h"
#include <stdio.h>
Timer timer;
void main_action(){
int interval = timer.read_ms();
timer.reset();
// Do something that takes longer than desired call_every time...
wait(1.5); // something like this
printf("trying to call every 1 second\r\n");
printf("but actually called after %d ms\r\n", interval);
}
int main() {
// creates a queue with the default size
EventQueue queue;
// events are simple callbacks
queue.call_every(1000, main_action);
timer.start();
// events are executed by the dispatch method
queue.dispatch();
}
Great answer Zoltan, this is the best API we have for checking for starvation. You can also use a LowPowerTimer if you want to make sure the device can enter low-power states, at the cost of losing microsecond accuracy.
In this case, I'm not sure the event queue could provide a better API, and using an external timer would give you more control over what condition you want to check for.
posted by 04 Jun 2018