Why did entering a lock on a UI thread trigger an OnPaint event?

Question

I came across something I simply don\'t understand. In my application I have several threads all adding (and removing) items to a shared collection (using a shared lock). Th

Answer 1

I found this question while having issue of blocking on wait handle. Answers to this gave me hint to implement next:

 public static class NativeMethods
{
    [DllImport("kernel32.dll", SetLastError = true)]
    internal static extern UInt32 WaitForSingleObject(SafeWaitHandle hHandle, UInt32 dwMilliseconds);
}

public static class WaitHandleExtensions
{
    const UInt32 INFINITE = 0xFFFFFFFF;
    const UInt32 WAIT_ABANDONED = 0x00000080;
    const UInt32 WAIT_OBJECT_0 = 0x00000000;
    const UInt32 WAIT_TIMEOUT = 0x00000102;
    const UInt32 WAIT_FAILED = INFINITE;

    /// 

    /// Waits preventing an I/O completion routine or an APC for execution by the waiting thread (unlike default `alertable`  .NET wait). E.g. prevents STA message pump in background. 
    /// 
    /// 
    /// 
    /// Why did entering a lock on a UI thread trigger an OnPaint event?
    /// 
    public static bool WaitOneNonAlertable(this WaitHandle current, int millisecondsTimeout)
    {
        if (millisecondsTimeout < -1)
            throw new ArgumentOutOfRangeException("millisecondsTimeout", millisecondsTimeout, "Bad wait timeout");
        uint ret = NativeMethods.WaitForSingleObject(current.SafeWaitHandle, (UInt32)millisecondsTimeout);
        switch (ret)
        {
            case WAIT_OBJECT_0:
                return true;
            case WAIT_TIMEOUT:
                return false;
            case WAIT_ABANDONED:
                throw new AbandonedMutexException();
            case WAIT_FAILED:
                throw new System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error());
            default:
                return false;
        }
    }
}