The documentation suggests I use nm-device-wifi-request-scan-async, but I don't understand how to understand when it's has finished scanning. What's the correct second parameter I should pass, how is it constructed and what do I pass to nm-device-wifi-request-scan-finish?
I've tried using nm-device-wifi-get-last-scan and determining whether the scan has just happened or the last scan was a long time ago, but it doesn't seem to update the time of the scan - i.e., after requesting the scan and printing out the time between nm-utils-get-timestamp-msec and the last scan, it only increases and and decreases only if I restart the whole program, for some reason...
All I really need is to request a scan every x seconds and understand whether it has happened or not. The deprecated synchronous functions seem to have allowed this with callback functions, but I don't understand async :(
nm_device_wifi_request_scan_async() starts the scan, it will take a while until the result is ready.
You will know when the result is ready when the nm_device_wifi_get_last_scan() timestamp gets bumped.
it only increases and and decreases only if I restart the whole program, for some reason...
last-scan should be in clock_gettime(CLOCK_BOOTTIME) scale. That is supposed to never decrease (unless reboot). See man clock_gettime.
but I don't understand async
The sync method does not differ from the async method in this regard. They both only kick off a new scan, and when they compete, NetworkManager will be about to scan (or start shortly). The sync method is deprecated for other reasons (https://smcv.pseudorandom.co.uk/2008/11/nonblocking/).
Related
I am trying to understand how the auto rescheduling logic is supposed to work.
The recommended values in nagios.cfg are:
auto_reschedule_checks=1
auto_rescheduling_interval=30
auto_rescheduling_window=45
Supposedly this is after they realized the default values (same as above but with window=180) had the potential to have checks that never actually get executed (See https://support.nagios.com/kb/print-19.html).
But.. How are these new values any different?
How I understand it, every 30sec, it takes the next 45sec of checks, finds checks that overlap, and reschedules those evenly across the 45sec.
Isnt it possible for a check to indefinitely get rescheduled into that last 15 seconds of the 45sec window?
Am I missing something? Do rescheduled checks get an elevated priority so they arent rescheduled again? Reading through the code, it doesnt appear they are given any special treatment.
Seems to me that the only way to prevent that is for the interval and window to be the same.
Which means maybe a couple checks occurring right at each 30sec transition may go unnoticed,
but Id rather that than what I am presuming the behavior is with the "recommended" interval=30sec , window=45sec.
Any insights would be helpful!
In my project, have a data provider, which provides data in every 2 milli seconds. Following is the delegate method in which the data is getting.
func measurementUpdated(_ measurement: Double) {
measurements.append(measurement)
guard measurements.count >= 300 else { return }
ecgView.measurements = Array(measurements.suffix(300))
DispatchQueue.main.async {
self.ecgView.setNeedsDisplay()
}
guard measurements.count >= 50000 else { return }
let olderMeasurementsPrefix = measurements.count - 50000
measurements = Array(measurements.dropFirst(olderMeasurementsPrefix))
print("Measurement Count : \(measurements.count)")
}
What I am trying to do is that when the array has more than 50000 elements, to delete the older measurement in the first n index of Array, for which I am using the dropFirst method of Array.
But, I am getting a crash with the following message:
Fatal error: Can't form Range with upperBound < lowerBound
I think the issue due to threading, both appending and deletion might happen at the same time, since the delegate is firing in a time interval of 2 millisecond. Can you suggest me an optimized way to resolve this issue?
So to really fix this, we need to first address two of your claims:
1) You said, in effect, that measurementUpdated() would be called on the main thread (for you said both append and dropFirst would be called on main thread. You also said several times that measurementUpdated() would be called every 2ms. You do not want to be calling a method every 2ms on the main thread. You'll pile up quite a lot of them very quickly, and get many delays in their updating, as the main thread is going to have UI stuff to be doing, and that always eats up time.
So first rule: measurementUpdated() should always be called on another thread. Keep it the same thread, though.
Second rule: The entire code path from whatever collects the data to when measurementUpdated() is called must also be on a non-main thread. It can be on the thread that measurementUpdated(), but doesn't have to be.
Third rule: You do not need your UI graph to update every 2ms. The human eye cannot perceive UI change that's faster than about 150ms. Also, the device's main thread will get totally bogged down trying to re-render as frequently as every 2ms. I bet your graph UI can't even render a single pass at 2ms! So let's give your main thread a break, by only updating the graph every, say, 150ms. Measure the current time in MS and compare against the last time you updated the graph from this routine.
Fourth rule: don't change any array (or any object) in two different threads without doing a mutex lock, as they'll sometimes collide (one thread will be trying to do an operation on it while another is too). An excellent article that covers all the current swift ways of doing mutex locks is Matt Gallagher's Mutexes and closure capture in Swift. It's a great read, and has both simple and advanced solutions and their tradeoffs.
One other suggestion: You're allocating or reallocating a few arrays every 2ms. It's unnecessary, and adds undue stress on the memory pools under the hood, I'd think. I suggest not doing append and dropsFirst calls. Try rewriting such that you have a single array that holds 50,000 doubles, and never changes size. Simply change values in the array, and keep 2 indexes so that you always know where the "start" and the "end" of the data set is within the array. i.e. pretend the next array element after the last is the first array element (pretend the array loops around to the front). Then you're not churning memory at all, and it'll operate much quicker too. You can surely find Array extensions people have written to make this trivial to use. Every 150ms you can copy the data into a second pre-allocated array in the correct order for your graph UI to consume, or just pass the two indexes to your graph UI if you own your graph UI and can adjust it to accommodate.
I don't have time right now to write a code example that covers all of this (maybe someone else does), but I'll try to revisit this tomorrow. It'd actually be a lot better for you if you made a renewed stab at it yourself, and then ask us a new question (on a new StackOverflow) if you get stuck.
Update As #Smartcat correctly pointed this solution has the potential of causing memory issues if the main thread is not fast enough to consume the arrays in the same pace the worker thread produces them.
The problem seems to be caused by ecgView's measurements property: you are writing to it on the thread receiving the data, while the view tries to read from it on the main thread, and simultaneous accesses to the same data from multiple thread is (unfortunately) likely to generate race conditions.
In conclusion, you need to make sure that both reads and writes happen on the same thread, and can easily be achieved my moving the setter call within the async dispatch:
let ecgViewMeasurements = Array(measurements.suffix(300))
DispatchQueue.main.async {
self.ecgView.measurements = ecgViewMeasurements
self.ecgView.setNeedsDisplay()
}
According to what you say, I will assume the delegate is calling the measuramentUpdate method from a concurrent thread.
If that's the case, and the problem is really related to threading, this should fix your problem:
func measurementUpdated(_ measurement: Double) {
DispatchQueue(label: "MySerialQueue").async {
measurements.append(measurement)
guard measurements.count >= 300 else { return }
ecgView.measurements = Array(measurements.suffix(300))
DispatchQueue.main.async {
self.ecgView.setNeedsDisplay()
}
guard measurements.count >= 50000 else { return }
let olderMeasurementsPrefix = measurements.count - 50000
measurements = Array(measurements.dropFirst(olderMeasurementsPrefix))
print("Measurement Count : \(measurements.count)")
}
}
This will put the code in an serial queue. This way you can ensure that this block of code will run only one at a time.
I have been making a labview program for kids to moniter energy production from various types of power sources. I have a condition where if they are underproducing a warning will fire, and if they are overproducing by a certian threshold, another warning will fire.
I would like to time how long throughout the activity, each type of warning is fired so each group will have a score at the end. This is just to simulate how the eventual program will behave.
Currently I have a timer which can derrive the amount of time the warning is true, but it will overwrite itself each time the warning goes off and on again.
So basically I need to to sum up the total time that the value has been true, even when it has flitted between true and false.
One method of tabulating the total time spent "True" would be exporting the Warning indicator from the While-loop using an indexed tunnel. If you also export from the loop a millisecond counter value of when the indicator was triggered, you can post process what will be an array of True/False values with the corresponding time at which the value transitioned.
The post processing could be a for-loop that keeps a running total of time spent true.
P.s. if you export your code as a VI snippet, others will be able to directly examine and modify the code without needing to remake it from scratch. See the NI webpage on the subject:
http://www.ni.com/white-paper/9330/en/
I would suggest going another way. Personally, I found the code you used confusing, since you subtract the tick count from the value in the shift register, which may work, but doesn't make any logical sense.
Instead, I would suggest turning this into a subVI which does the following:
Keep the current boolean value, the running total and the last reset time in shift registers.
Initialize these SRs on the first call using the first call primitive and a case structure.
If the value changes from F to T (compare the input to the SR), update the start time.
If it changes from T to F, subtract the start time from the current time and add that to the total.
I didn't actually code this now, so there may be holes there, but I'm leaving that as an exercise. Also, I would suggest making the VI reentrant. That way, you can simply call it a second time to get the same functionality for the second timer.
Someone can show me how to create a non-blocking timer to delete data of a struct?
I've this struct:
struct info{
char buf;
int expire;
};
Now, at the end of the expire's value, I need to delete data into my struct. the fact is that in the same time, my program is doing something else. so how can I create this? even avoiding use of signals.
It won't work. The time it takes to delete the structure is most likely much less than the time it would take to arrange for the structure to be deleted later. The reason is that in order to delete the structure later, some structure has to be created to hold the information needed to find the structure later when we get around to deleting it. And then that structure itself will eventually need to be freed. For a task so small, it's not worth the overhead of dispatching.
In a difference case, where the deletion is really complicated, it may be worth it. For example, if the structure contains lists or maps that contain numerous sub-elements that must be traverse to destroy each one, then it might be worth dispatching a thread to do the deletion.
The details vary depending on what platform and threading standard you're using. But the basic idea is that somewhere you have a function that causes a thread to be tasked with running a particular chunk of code.
Update: Hmm, wait, a timer? If code is not going to access it, why not delete it now? And if code is going to access it, why are you setting the timer now? Something's fishy with your question. Don't even think of arranging to have anything deleted until everything is 100% finished with it.
If you don't want to use signals, you're going to need threads of some kind. Any more specific answer will depend on what operating system and toolchain you're using.
I think the motto is to have a timer and if it expires as in case of Client Server logic. You need to delete those entries for which the time is expired. And when a timer expires, you need to delete that data.
If it is yes: Then it can be implemented in couple of ways.
a) Single threaded : You create a sorted queue based on the difference of (interval - now ) logic. So that the shortest span should receive the callback first. You can implement the timer queue using map in C++. Now when your work is over just call the timer function to check if any expired request is there in your queue. If yes, then it would delete that data. So the prototype might look like set_timer( void (pf)(void)); add_timer(void * context, long time_to_expire); to add the timer.
b) Multi-threaded : add_timer logic will be same. It will access the global map and add it after taking lock. This thread will sleep(using conditional variable) for the shortest time in the map. Meanwhile if there is any addition to the timer queue, it will get a notification from the thread which adds the data. Why it needs to sleep on conditional variable, because, it might get a timer which is having lesser interval than the minimum existing already.
So suppose first call was for 5 secs from now
and the second timer is 3 secs from now.
So if the timer thread only sleeps and not on conditional variable, then it will wake up after 5 secs whereas it is expected to wake up after 3 secs.
Hope this clarifies your question.
Cheers,
I have this code
n_userobject inv_userobject[]
For i = 1 to dw_1.Rowcount()
inv_userobject[i] = create n_userobject
.
.
.
NEXT
dw_1.rowcount() returns only 210 rows. Its so odd that in the range of 170 up, the application stop and crashes on inv_userobject[i] = create n_userobject.
My question, is there any limit on array or userobject declaration using arrays?
I already try destroying it after the loop so as to check if that will be a possible solution, but it is still crashing.
Or how can i be able to somehow refresh the userobject?
Or is there anyone out there encounter this?
Thanks for all your help.
First, your memory problem. You're definitely not running into an array limit. If I was to take a guess, one of the instance variables in n_userobject isn't being cleaned up properly (i.e. pointing to a class that isn't being destroyed when the parent class is destroyed) or pointing to a class that similarly doesn't clean itself up. If you've got PB Enterprise, I'd do a profiling trace with a smaller loop and see what is being garbage collected (there's a utility called CDMatch that really helps this process).
Secondly, let's face it, you're just doing this to avoid writing a reset method. Even if you get this functional, it will never be as efficient as writing your own reset method and reusing the same instance over again. Yes, it's another method you'll have to maintain whenever the instance variable list changes or the defaults change, but you'll easily gain that back in performance.
Good luck,
Terry.
I'm assuming the crash you're facing is at the PBVM level, and not a regular PB exception (which you can catch in your code). If I'm wrong, please add the exception details.
A loop of 170-210 iterations really isn't a large one. However, crashes within loops are usually the result of resource exhaustion. What we usually do in long loops is call GarbageCollect() occasionally. How often should it be called depends on what your code does - using it frequently could allow the use of less memory, but it will slow down the run. Read this for more.
If this doesn't help, make sure the error does not come from some non-PB code (imported DLL or so). You can check the stack trace during the crash to see the exception's origin.
Lastly, if you're supported by Sybase (or a local representative), you can send them a crash dump. They can analyze it, and see if it's a bug in PB, and if so, let you know when it was (or will be) fixed.
What I would normally do with a DataWindow is to create an object that processes the data in a row and call it for each row.
the only suggestion i have for this is to remove the rowcount from the for (For i = 1 to dw_1.Rowcount()) this will cause the code to recount the rows every time it uses one. get the count into a variable and then use the variable. it should run a bit better and be far more easy to debug.