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In practice, TrimExcess does nothing to "free memory" - look at the Reference Sources if you aren't sure: Reference Source[^]
You will find that in effect all it does is set the internal array to an empty array, it doesn't do anything "fancy" with the memory it no longer wants. Indeed, if you use TrimExcess to set a smaller size to the internal array, it will use more memory to do that, not less!
Don't mess with the GC - leave it alone and let it come in when it needs to. The best way to free memory is to set all references to the object to null and let the memory management handle it in it's own time. It's probably a lot better than you are at doing this! 
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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This explanation is not clear....please elaborate it if possible with example.
Indeed, if you use TrimExcess to set a smaller size to the internal array, it will use more memory to do that, not less!
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Look at the reference source that I linked to - it's the actual source code for the List<T> class.
Now look at what happens when you set a size half as big as it is at the moment, and follow that into the Capacity property setter. What does the code do when you halve the capacity?
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Calling GC.Collect() may not immediately release the memory. If you want to make sure it does that, you can do do this:
GC.Collect();
GC.WaitForPendingFinalizers();
Keep in mind that the WaitForPendingFinalizers method blocks the calling thread until it returns.
Like everyone else has said, you should probably leave the garbage collector alone, and be more vigilant about references to the object(s) in question. As long as another object holds a reference to another object, that referenced object remains in memory.
".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013
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what GC.WaitForPendingFinalizers(); does ? does it call garbage collector immediately or something else ?
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GC.WaitForPendingFinalizers Method (System) | Microsoft Docs[^]
".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013
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It is important to understand the difference between memory that is being used and memory that at one time was used. The first cannot be freed by any means. You must stop using it and when you do then it moves into the second category where it might be freed.
If your allocations are below 85,000 bytes then any allocation request will do a garbage collection itself if there is not enough free memory to meet the needs of the request. This will happen (basically) up until you run out of memory because you are 'using' all of it. It will not free memory if you are using(pointing) to it.
If the allocated size is larger than 85,000 bytes (bytes, not chars, ints, etc) then the memory handling is slightly different in that between allocating and free allocations, if those are not somewhat sequential one can end up with having enough free memory but not actually succeeding in getting it because the memory is fragmented. For more on that you must learn quite a bit about how "heaps" in general work (not just C#) and how those can become fragmented. Once you understand that then you can look at the C# "Large Object Heap".
Your loop has 1,000,000 items and for a 64 bit machine you would need to have an item in every member of that list and each item would need to be about 10,000 bytes in size before I would suspect it to be a problem.
Mou_kol wrote: button2_Click
Regardless of the above however that method suggests a UI. And a UI list with a million items in it is a BAD design.
Any UI with a list that attempts to contain more than 1000 items EVER, is a BAD design. And that might even be high.
Learn how to do paging instead. Also learn how to provide a method that allows the user to provide criteria and search for what they want in the list.
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What nobody has asked or said anything about is "What are you using to determine if memory is being freed?"
If you're looking in Task Manager to see how much memory your app is using, DO NOT DO THAT! Task Manager is lying to you. It's showing you how much memory is RESERVED for your app, not how much it's actually using.
When you start a .NET app, the .NET Common Language Runtime (CLR) gets a block of memory from Windows and makes that block the "managed heap". The code for you app is loaded and every object your app creates is allocated using memory from the managed heap. When your app is freeing objects up, the memory is returned to the managed heap, NOT to Windows. If the CLR needs more memory for your app, its asks Windows for another block of memory. If Windows needs more memory, it can ask the CLR to return any free memory its can spare, which the CLR will happily return.
Task Manager is showing you the memory the CLR is holding onto, not how much your app is actually using. If you want to see how much your app is using, you have to use PerfMon and the .NET Memory counters.
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private void button2_Click(object sender, EventArgs e)
{
var before = System.Diagnostics.Process.GetCurrentProcess().VirtualMemorySize64;
List<string> lst1 = new List<string>();
for (int i = 0; i <= 1000000; i++)
{
lst1.Add("Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test ");
}
var after = System.Diagnostics.Process.GetCurrentProcess().VirtualMemorySize64;
lst1.Clear();
lst1.TrimExcess();
var current = System.Diagnostics.Process.GetCurrentProcess().VirtualMemorySize64;
}
i saw TrimExcess() clear memory for list instantly and it is bit better than list = null & GC.Collect....am i right?
one request that please tell me what List TrimExcess() does and when to use it ?
please come with a example which explain the objective of List TrimExcess() .
i want to understand the actual usage of TrimExcess() function.
thanks
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I have a form with a lot of controls on it like Buttons, TextBoxes, Panels and so on, and I've defined some properties such as Button_BackColor, Panel_Width, Label_ForColor, App_Font in the Settings.settings file. All things work at runtime but I want to apply this settings as design time, so that I could feel it without running. What can i do?
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As I understood those new Properties are belonging to the Form / are declared on the Form - I call it myForm.
If you want to see them at DesignTime you must use this Form as a template - that means you must derive your new Form from this (allready defined) myForm.
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I know that, but modifying template is not so easy in visual studio. In the android studio by changing XML file, All change would be applied all element at design time. but it seems, it's not good way in visual studio to do this.
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This is the answer:
https://stackoverflow.com/a/55632847/579381
thanks anyway.
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HI,
I have one circle with radius & center point, I have to place multiple circles with radius known but center point unknown (needs to be calculated based on 1st circle-non intersecting). I can move circle in x direction till it is not intersecting with 1st circle. Similarly 3rd circle, 4th circle. NOw 5th circle needs to moved in y direction till it is non intersecting, (7th,8th,9th in increasing value of x & y value same as that of 5th. Please if anyone has some code , can please share ?
Thanks
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We are more than willing to help those that are stuck: but that doesn't mean that we are here to do it all for you! We can't do all the work, you are either getting paid for this, or it's part of your grades and it wouldn't be at all fair for us to do it all for you.
So we need you to do the work, and we will help you when you get stuck. That doesn't mean we will give you a step by step solution you can hand in!
Start by explaining where you are at the moment, and what the next step in the process is. Then tell us what you have tried to get that next step working, and what happened when you did.
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Use WPF and a DockPanel or a WrapPanel or a combination to load Ellipses into the panel(s): left-to-right, bottom up. In whatever order and direction that works.
Hosted in a top level Grid and with "Stretch" alignment, the "circles" will rearrange as the Window is resized.
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal
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Hi,
if all circles have the same radius R (you did not state this essential information) then it is very simple:
1. for an orthogonal packing, the center will move by 2*R in both directions, so all centers form a simple grid.
2. for the "triangular packing" shown in the reference Dave gave you, the center distances are 2*R in one direction and R*SQRT(3) in the transversal direction.
Proof: the centers form equilateral triangles, so all angles are 60 degrees, and SIN(60)=0.5*SQRT(3).
Coding this is up to you.
If the radii are different, you have a special (and not an easy) knapsack problem!
modified 11-Apr-19 8:43am.
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I defined a CrawlerTimeoutException that is inherited from task exception， when I throw it in my code，I can't catch it in the main thread， the code is below：
try
{
Random rand = new Random();
await Task.Delay(rand.Next(300, 1000));
var webcontent = await task.Crawl().Timeout(timeout);
}
catch (CrawlerTimeoutException)
{
}
catch (Exception exp)
{
}
I threw the
CrawlerTimeoutException in function
task.Crawl().Timeout(timeout);
the code is below：
public static Task<T> Timeout<T>(this Task<T> task, int millisecondsTimeout)
{
return Task.Factory.StartNew(() =>
{
bool succ = task.Wait(millisecondsTimeout);
if (succ)
return task.Result;
else
throw new CrawlerTimeoutException("Task timeout");
});
}
when it times out, it will throw a exception, but the program will crash because it says: there is a exception that user-unhandled.
I don't know the reason, because I catch it in the main thread twice, but still don't catch it.
if you know the reason, please tell me！
thanks so much!
modified 10-Apr-19 0:04am.
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I just replaced the Task.Factory.StartNew() by Task.run() in Timeout function following this, but it didn't work for my program.
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THreads get complicated, but what it boils down to is that each thread has its own "execution space" which are completely separate: an exception thrown in ThreadA will not be caught in the main thread because they are totally separate. Think about it: the main thread has a totally separate stack to ThreadA so which try...catch block should catch the ThreadA exception?
YOu can do it - the simplest solution is to use a BackgroundWorker which can catch teh error and "pass it on up" to the calling thread:
private void FrmMain_Shown(object sender, EventArgs e)
{
BackgroundWorker work = new BackgroundWorker();
work.DoWork += Work_DoWork;
work.RunWorkerCompleted += Work_RunWorkerCompleted;
work.RunWorkerAsync();
}
private void Work_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
Exception ex = e.Error;
if (ex != null) Console.WriteLine(ex.Message);
}
private void Work_DoWork(object sender, DoWorkEventArgs e)
{
throw new NotImplementedException();
}
But there are also ways using asynchronous delegates and the Task Parallel Library, but I haven't needed to use those yet.
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Yeah, exceptions thrown in an asynchronous context do not trigger exceptions in a synchronous one (I mean, how could it?)
So, first off, the "built-in" mechanism to do what you're trying to do here is to define a CancellationTokenSource with a timeout and pass that token to your task. You don't need to reinvent the wheel here.
Secondly, there are 2 contexts that you need to consider when handling exceptions in tasks. The first is a try-catch block as part of the task itself for block-level handling, and the second is an external handler for logging or any appropriate module-level responses. The block-level is the basic try-catch we know and love; the external looks sort of like this:
class Program
{
static void Main(string[] args)
{
Task.Run(() =>{throw new NotImplementedException();})
.ContinueWith(task => {
if(task.IsFaulted)
{
Console.WriteLine($"Exception thrown: {task.Exception?.Message}");
}
else
{
Console.WriteLine("You shouldn't see this"));
}
});
var k = Console.ReadLine();
}
}
"Never attribute to malice that which can be explained by stupidity."
- Hanlon's Razor
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One simple way to fix your method would be:
public static async Task<T> Timeout<T>(this Task<T> task, int millisecondsTimeout)
{
Task timeoutTask = Task.Delay(millisecondsTimeout);
Task completedTask = await Task.WhenAny(task, timeoutTask).ConfigureAwait(false);
if (completedTask == timeoutTask) throw new TimeoutException("Task timeout");
return await task.ConfigureAwait(false);
}
Alternatively, as Nathan suggested, you can use a CancellationTokenSource to cooperatively cancel your task when the timeout expires:
Cancel Async Tasks after a Period of Time (C#) | Microsoft Docs[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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