Detailed explanation of the writing of classic memory leak scenarios in C#

Memory leak refers to the inability to release the memory in the program correctly, which causes the program to continuously occupy memory without releasing, which may ultimately lead to insufficient system resources.

In C#, common memory leak scenarios include:

Event handler is not removed correctly: When using events, if the event handler is not removed correctly, the event subscriber object cannot be garbage collected, resulting in a memory leak.

Circular reference: Objects refer to each other, but no reference relationship is released, resulting in the object being unable to be garbage collected.

Long-lifetime object holds references to short-lifetime object: If a long-lifetime object holds references to a short-lifetime object, and this short-lifetime object should actually be recycled, it will lead to memory leaks.

Static collection: A large number of objects are stored in the static collection and are not cleaned up in time, resulting in the object being unable to be released.

Large objects or large arrays are not released: When using large objects or large arrays, if not released in time, memory leaks may occur.

Using unmanaged functions When using unmanaged resources (such as memory, handles, etc.), these resources must be manually released. If the resource is not released correctly, it will cause a memory leak.

Causes of memory leaks usually include:

• Error object reference management
• Weak reference not used correctly
• Cache not cleaned correctly
• Large objects are not handled correctly
• Object pool is not managed correctly

To find and analyze memory leaks, you can take the following steps:

• Use memory analysis tools: tools such as .NET Memory Profiler, ANTS Memory Profiler, etc. can help detect memory leaks and locate problem code.
• Analyze stack information: By viewing stack information, you can understand the creation and release process of objects, helping to locate the causes of memory leaks.
• Check code logic: Check the code carefully to ensure that the object's reference relationship and lifecycle management are correct.

Common error examples:

Memory leaks caused by event handler not properly removed:

using System;

public class EventLeakExample
{
    public event EventHandler MyEvent;

    public void Subscribe()
    {
        MyEvent += MyEventHandler;
    }

    public void Unsubscribe()
    {
        // Forgot to remove the event handler        // MyEvent -= MyEventHandler;
    }

    private void MyEventHandler(object sender, EventArgs e)
    {
        ("Event handled.");
    }
}

class Program
{
    static void Main(string[] args)
    {
        EventLeakExample example = new EventLeakExample();
        ();

        // The mock object is no longer needed, but is not released correctly        // ();

        // If you do not call the Unsubscribe method, it will cause memory leaks        // Event handler still maintains a reference to the example object, making it impossible to garbage collect
        example = null; // At this time the example object should be released, but the memory leak may occur because the event handler is not removed.
        // Garbage collection may not be possible to release the example object        ();
        ();
        ();

        ("Memory leak check complete. Press any key to exit.");
        ();
    }
}

Memory leaks that may occur when using unmanaged function calls

using System;
using ;

public class UnmanagedLeakExample
{
    [DllImport("")]
    private static extern IntPtr LocalAlloc(int uFlags, IntPtr uBytes);

    [DllImport("")]
    private static extern IntPtr LocalFree(IntPtr hMem);

    private IntPtr _unmanagedMemory;

    public void AllocateMemory()
    {
        // Allocate unmanaged memory        _unmanagedMemory = LocalAlloc(0x40, new IntPtr(1000)); // LPTR: zero-initialized, 1000 bytes
    }

    public void FreeMemory()
    {
        // Release unmanaged memory        if (_unmanagedMemory != )
        {
            LocalFree(_unmanagedMemory);
            _unmanagedMemory = ;
        }
    }

    ~UnmanagedLeakExample()
    {
        // Release unmanaged resources in destructor        FreeMemory();
    }
}

class Program
{
    static void Main(string[] args)
    {
        UnmanagedLeakExample example = new UnmanagedLeakExample();
        ();

        // Unmanaged resources are not released after use        // ();

        example = null; // At this time the example object should be released, but due to the unmanaged resource not being released, memory leaks may occur.
        // Garbage collection may not be possible to release the example object        ();
        ();
        ();

        ("Memory leak check complete. Press any key to exit.");
        ();
    }
}

To avoid memory leaks caused by unmanaged functions, you need to ensure the following:

Properly release unmanaged resources: Use methods in the Marshal class to release unmanaged resources, such as releasing global memory, freeing
COM objects, etc.

Check unmanaged code: For cases where unmanaged functions are called, you need to make sure that memory management in the unmanaged code is correct and there are no memory leaks.

Use secure encapsulation: Encapsulate unmanaged functions in a secure managed class and release unmanaged resources in the destructor of that class to ensure that the resources are released correctly.

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