New to Go and building a simple LRU cache in Go to get used to syntax and Go development.
Having an issue with the MoveToFront list method, it fails on the following check in the MoveToFront body
if e.list != l || l.root.next == e
I want to move the element (e) to the front of the list when I retrieve it from cache , like this
if elem, ok := lc.entries[k]; ok {
lc.list.MoveToFront(elem) // needs fixing
return elem
}
return nil
The Code can be seen here on line 32 the issue occurs
https://github.com/hajjboy95/golrucache/blob/master/lru_cache/lrucache.go#L32
There seem to be two problems, to me. First, this isn't how the List data type is meant to be used: lc.list.PushFront() will create a List.Element and return a pointer to it. That's not fatal, but at the least, it is kind of annoying—the caller has to dig through the returned List.Element when using Get, instead of just getting the value.
Meanwhile, presumably the failure you see is because you remove elements in Put when the LRU-list runs out of space, but you don't remove them from the corresponding map. Hence a later Put of the just-removed key will try to re-use the element in place, even though the element was removed from the list. To fix this, you'll need to hold both key and value. (In my simple experiment I did not see any failures here, but the problem became clear enough.)
I restructured the code somewhat and turned it into a working example on the Go Playground. I make no promises as to suitability, etc.
Related
I am implementing logging functionality in Unreal Engine 4.27 (in C++). A key part of my code is a function that is called once per game-tick. This function is responsible for iterating over an array of actors that I would like to log data for, checking whether a new log entry should be written at this point in time and calling the necessary functions to do that.
I am iterating over elements of a TArray of UStructs: LogObject->LoggingInfo = TArray<FActorLoggingInformation>. This array is defined as a UProperty of LogObject. In the loop I have to change the values of the elements so I want to work with the original items and "label" the current item as "ActorLoggingInfo". I have seen this done generally in cpp and also with TArrays. And yet my code does not work, there is no error message, but ActorLoggingInfo is undefined, thus the if-condition is never met.
This is the for-loop:
for (FActorLoggingInformation& ActorLoggingInfo : LogObject->LoggingInfo) {
if (ActorLoggingInfo.LogNextTick == true) {
ActorLoggingInfo.LogNextTick = false;
...
}
...
}
This is the definition of FActorLoggingInformation:
USTRUCT(BlueprintType)
struct FActorLoggingInformation
{
GENERATED_BODY()
public:
FActorLoggingInformation()
{
}
FActorLoggingInformation(int32 LogTimer, AActor* Actor, FString LogName)
{
this->LogTimer = LogTimer;
this->LogNextTick = false;
...
}
// Specifies Logging Frequency in ms
UPROPERTY(BlueprintReadOnly, VisibleAnywhere)
int32 LogTimer;
bool LogNextTick;
...
};
This is the debugger at run-time:
Additional Notes:
1. Something that consistently works for me is omitting the &, using:
for (FActorLoggingInformation ActorLoggingInfo : LogObject->LoggingInfo)
However, this is creating useless duplicates on a per-tick basis and complicates applying changes to the original objects from within in the for-loop, so it is not a viable option.
2. I have also tried auto& instead of FActorLoggingInformation& as used in the examples above, but I encountered the same issue, so I thought it would be best to be as explicit as possible.
I would be very thankful if you had any ideas how I can fix this :)
Thanks in advance!
Thanks to Avi Berger for helping me find my problem!
In fact, ActorLoggingInfo was actually never undefined and the code within the body of the if-clause was also executed (it just didn't do what it was intended to do).
When stepping through the code in the debugger it never showed the steps within the if-body and ActorLoggingInfo was shown as undefined so when no logs were written, I assumed it was something to do with that instead of my output function not working properly. So lesson learnt, do not blindly trust the debugger :)
This is my code in order to get the name of the item which has been selected in my CListViewCtrl:
LVITEM item = { LVIF_PARAM };
CString itemText;
clistViewCtrl.GetSelectedItem(&item);
clistViewCtrl.GetItemText(item.iItem, item.iSubItem, itemText);
Note that this code is working. I recently did another project, where I grabbed the name in exactly this way, however, I had no problems there with any assertion fails.
When I execute this with my current project, I always get a debug assertion:
"File: ... atlctrls.h"
Line: 3242
Expression: (GetStyle() & 0x0004) != 0
Even though the expression already states it pretty much, here is the line causing the failure:
ATLASSERT((GetStyle() & LVS_SINGLESEL) != 0);
I have barely any idea what the problem is. As I said, the exact same code worked on my other project, and I just went through both, trying to find any differences which could cause this behaviour, but nothing caught my eye.
Honestly, I don't even know if this is related to my code at all, considering the two compared elements seem to be predefined.
My first guess would have been that this part is being called before the items are created, but all items in the listview are created at the point I try to call this code passage.
Can anyone point me to a solution?
Your control is not created with style flag LVS_SINGLESEL. So calling GetSelectedItem is causing an assert. In case of multi selection use GetFirstSelectedItem and GetNextSelectedItem instead of GetSelectedItem. For single selection you can continue useing GetSelectedItem, but you have to add LVS_SINGLESEL style flag to your control.
I'm getting the error Element XMLZONE is undefined in REQUEST a few dozen times a day.
PageDisplay.cfm calls request.xmlzone which is set via the page ZoneManager.cfm, using the following (cut down) code
<cfscript>
variables.aZoneInfo = XmlSearch(application.xmlZones, "//zone[position() = 1]");
try {
request.xmlZone = ToString(variables.aZoneInfo[1]);
}
catch(any expt)
{
variables.objZoneDAO = CreateObject("component", "#application.sComponentDir#ZoneDAO").init(application.sDSN);
variables.objZoneDAO.Read(variables.objZone, 1); }
</cfscript>
Now, the XML will never ever change so is it worth adding the XML file/node to PageDisplay.cfm as a variable? I'd also like to know why it fails - any reason why?
Thanks,
JJ
Well, if the call to ToString(variables.aZoneInfo[1]); fails, then request.xmlZone won't get set. It's doubtful toString() itself will fail, but if variables.aZoneInfo isn't an array with at least one element, then that'll cause you grief. You should be checking this, rather than assuming it.
If it's essential that request.xmlZone is set, then you need to do more in your catch block than what you're currently doing. At the very least you should be logging the exception that was caught, so that when you go "I wonder why that happened?" you have a log to refer to.
I suspect your application is timing out, and when you're doing your xmlSearch(), application.xmlZones doesn't contain what you think it contains. But that's a guess.
I am trying to use the Google geocoder to do a reverse-geocoder lookup. I am running the exact same command on 8 values, and I am only having an error on two of them, which has me confused as one of the failing values is identical to one of the working values. (The 'working' values aren't really working- they still return a value of undefined from the 'formatted_address' field, but they aren't throwing errors). The command that I am running is as follows:
geocoder.geocode({latLng: new google.maps.LatLng(machineList[i].y, machineList[i].x)}, function(results, status) { address = results[0]; });
I am receiving a type error from Javascript, claiming that results is null. I'm not sure why this is happening. Any ideas?
Well, it turns out this was a timing issue. The geocode() command was taking longer to complete for certain locations than for others, which caused the value to show up as null. I ended up eliminating the problem by moving all the subsequent code into the callback function (I hadn't done this earlier because the whole thing is running inside of a loop, and I was having some difficulty getting it to pass in the iterator as a parameter). Now everything seems to be working well and the locations are showing up as they should.
I'm not getting any error messages, simply my vector is not populating. Looking at the vector in the watch list, nothing is being copied. Why is this?
I've tried two ways.
The first
std::vector<Point3D*> hitpoints;
local_hit_point = sr.local_hit_point; //local_hit_point class Point3D
hitpoints.push_back(local_hit_point);
The second way I tried to use pointers
std::vector<Point3D*> hitpoints;
Point3D* hittingpoint_ptr = new Point3D;
local_hit_point = sr.local_hit_point;
hittingpoint_ptr = &local_hit_point;
hitpoints.push_back(hittingpoint_ptr);
I got vectors in other places in my code which work. Am I really just being daft, but I can't seem to figure out why its not working.
My best guess is that you have an issue with you debugger..
First Suggestion;
Clear everything in your watchlist because they can change the behaviour of the execution
check it again..
Second suggestion;
Create a new project and write a simple code like the one above and see whether your vector is populating..If this simple project works, you should provide us more code and details..
simply my vector is not populating.
It is populating. However
Looking at the vector in the watch list ...
I used hitpoint.size()
Results of function/method calls (size() is a method) are not automatically updated in visual studio watch list (because you haven't told what os/compiler you use I had to assume it is visual studio). I.e. if you enter function call into watch list, it'll calculate results, but will not call function again until you manually refresh it. Instead of function call, add vector itself into watch list.