What is difference between following codes
void foo()
{
CRITICAL_SECTION csection;
InitializeCriticalSection(&csection);
EnterCriticalSection(&csection);
// some code goes here
delete csection;
}
void foo()
{
CRITICAL_SECTION csection;
InitializeCriticalSection(&csection);
EnterCriticalSection(&csection);
// some code goes here
DeleteCriticalSection(&csection);
}
which is best way to dispose the csection object ?
Keyword delete is for things allocated with new or gcnew, only. The only way to clean up a critical section is the DeleteCriticalSection method.
Related
Assume I have a class C that holds resources that need to be closed as member variables.
public class C {
private ClosableResource1 closableResource1;
private ClosableResource2 closableResource2;
.....
public C(){
closableResource1 = new ClosableResource1();
closableResource2 = new ClosableResource2();
.....
// some logic that can fail
}
close(){
closableResource1.close()
closableResource2.close()
.....
}
}
If the constructor succeeds I can be sure that close() will be called eventually by some entity manager and all the resources will be freed.
But how can I make sure I close the resources when the constructor fails? The failure can happen because I have additional logic in the constructor that can throw exception or I get some RuntimeException outside of my control?
Some things I though of:
Wrapping the constructor body with a try-catch block. Then, assuming I have a lot of closable members I'll have to have a big if statement in the catch block checking which resources were already initializing and only close them.
Offloading the ClosableResources creation to some init() function. Then I would have to make sure init() succeeded every time I try to use the object.
Is there some elegant solution? Or is this much more implementation specific then that?
You can do something like below:
public class C {
private List<AutoCloseable> closableResources = new ArrayList();
private ClosableResource1 closableResource1;
private ClosableResource2 closableResource2;
.....
public C() {
closableResource1 = new ClosableResource1();
closableResources.add(closableResource1)
closableResource2 = new ClosableResource2();
closableResources.add(closableResource2);
.....
try {
// some logic that can fail
} catch(Exception e) {
close();
}
}
close(){
for (AutoCloseable closableResource : closableResources) {
if (closableResource != null) {
closableResource.close();
}
}
}
}
Surrounding your code with try-catch and closing all your resources in catch is the correct solution here. Also read about method finalize() (Here is one tutorial). In general, I would recommend one method that cleans up all the resources (like you suggested method close(), I would call it though cleanup()) and call that method in your catch section and in your finalize() method
I asked and answered a very similar question here. It is very important that a constructor either succeeds or fails completely i.e. leaving no resources open. In order to achieve that I would follow each resource creation statement by a try-catch block. The catch block closes the resource and rethrows the exception so it is not lost:
public C() {
closableResource1 = new ClosableResource1();
closableResource2 = new ClosableResource2();
try {
// .....
// some logic that can fail and throw MyCheckedException or some RuntimeException
} catch (RuntimeException | MyCheckedException e) {
try {closableResource1.close();} catch (Exception ignore) {}
try {closableResource1.close();} catch (Exception ignore) {}
throw e;
}
}
If creating a resource can fail you need nested try-catch blocks as demonstrated here.
Here's a wild idea: create a class called something like DefusableCloser (that you can "defuse", like an explosive device being made safe):
class DefusableCloser implements AutoCloseable {
boolean active = true;
final AutoCloseable closeable;
DefusableCloser(AutoCloseable closeable) {
this.closeable = closeable;
}
#Override public void close() throws Exception {
if (active) closeable.close();
}
}
Now you can use this in a try-with-resources block:
c1 = new CloseableResource();
try (DefusableCloseable d1 = new DefusableCloseable(c1)) {
c2 = new CloseableResource();
try (DefusableCloseable d2 = new DefusableCloseable(c2)) {
// Do the other stuff which might fail...
// Finally, deactivate the closeables.
d1.active = d2.active = false;
}
}
If execution doesn't reach d1.active = d2.active = false;, the two closeables (or one, if the exception was in creating the second resource) will be closed. If execution does reach that line, they won't be closed and you can use them.
The advantage of doing it like this is that the exceptions will be correctly handled.
Note that the ordering is important: don't be tempted to create the two CloseableResources first, then the two DefusableCloseables: doing that won't handle an exception from creating the second CloseableResource. And don't put the creation of the CloseableResources into the TWR, as that would guarantee their closure.
For closing the resources in your class' close() method, you can also use try-with-resources to ensure that both resources are closed:
try (c1; c2) {}
You don't actually have to declare a new variable in the TWR syntax: you can just effectively say "close the resource for this existing variable afterwards", as shown here.
When I use the IDEA, type the if/for/while, the parentheses will auto added.But CLion will not auto complete.
IDEA
CLion
How to solve this problem?
You need to use complete statement (Ctrl+Shift+Enter).
void foo() {
if|<Ctrl+Shift+Enter>
}
generates
void foo() {
if (true|<Ctrl+Shift+Enter>) {
}
}
one more complete moves you into the block:
void foo() {
if (true) {
|
}
}
It can be found in Settings/Editor/General/Smart Keys (Or just go to Help-> Find -> Smart Keys)
There you have an option to check Home, End (on blank line), Insert pair bracket, etc. Check Insert pair bracket. This should do it.
I'm working on a project for an intro to programming class, and I've run into a slight problem. We're making a side scroller, and I'm working on the score counter right now. My issue is that when I try to create a reference to the counter class in anything other than the act method(called once every frame) I get a null pointer exception error. You can download the zip file with my code in it here if you want to take a look.
EDIT:
Here's the offending code:
public class HeroMissile extends Missiles
{
/**
* Act - do whatever the HeroMissile wants to do. This method is called whenever
* the 'Act' or 'Run' button gets pressed in the environment.
*/
public void act()
{
move(8);
remove();
}
public void remove() {
if(isTouching(Drone.class)) {
removeTouching(Drone.class);
getWorld().addObject(new Explosion(), getX(), getY());
getWorld().removeObject(this);
addScore();
return;
}
}
public void addScore() {
City cityWorld = (City) getWorld();
**Counter scoreCounter = cityWorld.getCounter();**
scoreCounter.add(1);
}
}
You are calling getWorld() [in addScore()] after you removed yourself from the world. In this case, getWorld() will return null, so you will get a null pointer exception. Try changing the order in remove() to add the score before you remove yourself from the world.
In my title screen, i have a code saying that the first controller using A is the PlayerIndex.one.
Here is the code:
public override void HandleInput(InputState input)
{
for (int anyPlayer = 0; anyPlayer <4; anyPlayer++)
{
if (GamePad.GetState((PlayerIndex)anyPlayer).Buttons.A == ButtonState.Pressed)
{
FirstPlayer = (PlayerIndex)anyPlayer;
this.ExitScreen();
AddScreen(new Background());
}
}
}
My question is: How can i use the "FirstPlayer" in other classes? (without this, there is no interest in this code)
I tried the Get Set thing but i can't make it work. Does i need to put my code in another class? Do you use other code to make this?
Thanks.
You can make a static variable say : SelectedPlayer,
and assign first player to it!
then you can call the first player through this class,
for example
class GameManager
{
public static PlayerIndex SelectedPlayer{get;set;}
..
..
..
}
and right after the loop in your code, you can say:
GameManager.SelectedPlayer = FirstPlayer;
I hope this helps, if your code cold be clearer that would be easier to help :)
Ok, so to do this properly you're going to have to redesign a little.
First off, you should be checking for a new gamepad input (i.e. you should be exiting the screen only when 'A' has been newly pressed). To do this you should be storing previous and current gamepad states:
private GamePadState currentGamePadState;
private GamePadState lastGamePadState;
// in your constructor
currentGamePadState = new GamePadState();
lastGamePadState = new GamePadState();
// in your update
lastGamePadState = currentGamePadState;
currentGamePadState = GamePad.GetState(PlayerIndex.One);
Really what you need to do is modify your class that deals with input. The basic functionality from your HandleInput function should be moved into your input class. Input should have a collection of functions that test for new/current input. For example, for the case you posted:
public Bool IsNewButtonPress(Buttons buton)
{
return (currentGamePadState.IsButtonDown(button) && lastGamePadState.IsButtonUp(button));
}
Then you can write:
public override void HandleInput(InputState input)
{
if (input.IsNewButtonPress(Buttons.A)
{
this.ExitScreen();
AddScreen(new Background());
}
}
Note: this will only work for one controller. To extend the implementation, you'll need to do something like this:
private GamePadState[] currentGamePadStates;
private GamePadState[] lastGamePadStates;
// in your constructor
currentGamePadStates = new GamePadState[4];
currentGamePadStates[0] = new GamePadState(PlayerIndex.One);
currentGamePadStates[1] = new GamePadController(PlayerIndex.Two);
// etc.
lastGamePadStates[0] = new GamePadState(PlayerIndex.One);
// etc.
// in your update
foreach (GamePadState s in currentGamePadStates)
{
// update all of this as before...
}
// etc.
Now, you want to test every controller for input, so you'll need to generalise by writing a function that returns a Bool after checking each GamePadState in the arrays for a button press.
Check out the MSDN Game State Management Sample for a well developed implementation. I can't remember if it supports multiple controllers, but the structure is clear and can easily be adapted if not.
I have a Windows Workflow application that uses classes I've written for COM automation. I'm opening Word and Excel from my classes using COM.
I'm currently implementing IDisposable in my COM helper and using Marshal.ReleaseComObject(). However, if my Workflow fails, the Dispose() method isn't being called and the Word or Excel handles stay open and my application hangs.
The solution to this problem is pretty straightforward, but rather than just solve it, I'd like to learn something and gain insight into the right way to work with COM. I'm looking for the "best" or most efficient and safest way to handle the lifecycle of the classes that own the COM handles. Patterns, best practices, or sample code would be helpful.
I can not see what failure you have that does not calls the Dispose() method. I made a test with a sequential workflow that contains only a code activity which just throws an exception and the Dispose() method of my workflow is called twice (this is because of the standard WorkflowTerminated event handler). Check the following code:
Program.cs
class Program
{
static void Main(string[] args)
{
using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
AutoResetEvent waitHandle = new AutoResetEvent(false);
workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e)
{
waitHandle.Set();
};
workflowRuntime.WorkflowTerminated += delegate(object sender, WorkflowTerminatedEventArgs e)
{
Console.WriteLine(e.Exception.Message);
waitHandle.Set();
};
WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(WorkflowConsoleApplication1.Workflow1));
instance.Start();
waitHandle.WaitOne();
}
Console.ReadKey();
}
}
Workflow1.cs
public sealed partial class Workflow1: SequentialWorkflowActivity
{
public Workflow1()
{
InitializeComponent();
this.codeActivity1.ExecuteCode += new System.EventHandler(this.codeActivity1_ExecuteCode);
}
[DebuggerStepThrough()]
private void codeActivity1_ExecuteCode(object sender, EventArgs e)
{
Console.WriteLine("Throw ApplicationException.");
throw new ApplicationException();
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
// Here you must free your resources
// by calling your COM helper Dispose() method
Console.WriteLine("Object disposed.");
}
}
}
Am I missing something? Concerning the lifecycle-related methods of an Activity (and consequently of a Workflow) object, please check this post: Activity "Lifetime" Methods. If you just want a generic article about disposing, check this.
Basically, you should not rely on hand code to call Dispose() on your object at the end of the work. You probably have something like this right now:
MyComHelper helper = new MyComHelper();
helper.DoStuffWithExcel();
helper.Dispose();
...
Instead, you need to use try blocks to catch any exception that might be triggered and call dispose at that point. This is the canonical way:
MyComHelper helper = new MyComHelper();
try
{
helper.DoStuffWithExcel();
}
finally()
{
helper.Dispose();
}
This is so common that C# has a special construct that generates the same exact code [see note] as shown above; this is what you should be doing most of the time (unless you have some special object construction semantics that make a manual pattern like the above easier to work with):
using(MyComHelper helper = new MyComHelper())
{
helper.DoStuffWithExcel();
}
EDIT:
NOTE: The actual code generated is a tiny bit more complicated than the second example above, because it also introduces a new local scope that makes the helper object unavailable after the using block. It's like if the second code block was surrounded by { }'s. That was omitted for clarify of the explanation.