Using windows' CreateEvent() function from java using JNA

Question

I've written the following class to wrap the creation of a win32 event object

import com.sun.jna.*;
import com.sun.jna.Native;
import com.sun.jna.platform.win32.*;
import com.sun.jna.platform.win32.Kernel32;

/**
 * Wraps a (newly-created) native win32 event object and allows you to signal it.
 * 
 * The created event object is manual-reset and is initially un-set.
 */
public final class Win32Event
{
    private static final Kernel32 INSTANCE = (Kernel32) Native.loadLibrary("Kernel32", Kernel32.class);

    private WinNT.HANDLE m_handle = null;

    public Win32Event(String in_eventName)
    {
        assert null != in_eventName;

        m_handle = INSTANCE.CreateEvent(null, true, false, in_eventName);

        assert !Pointer.NULL.equals(m_handle.getPointer());
    }

    public void signal()
    {
        assert isValid();

        INSTANCE.SetEvent(m_handle);
    }

    /**
     * @return True if the event handle hasn't been freed with free().
     */
    public boolean isValid()
    {
        return null != m_handle;
    }

    /**
     * Frees the wrapped event handle. This must be done to prevent handle leaks.
     */
    public void free()
    {
        if (isValid())
        {
            INSTANCE.CloseHandle(m_handle);

            m_handle = null;
        }
    }

    @Override
    protected void finalize()
    {
        free();
    }
}

I'm using jna 3.3 on a windows 7 machine, and when I try to create an instance of this class, I get the following stack trace.

Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'CreateEvent': The specified procedure could not be found.

at com.sun.jna.Function.(Function.java:179) at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:347) at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:327) at com.sun.jna.Library$Handler.invoke(Library.java:203) at $Proxy0.CreateEvent(Unknown Source) at Win32Event.(Win32Event.java:23)

I'm really new to JNA, not sure what I'm doing wrong.

Answer 1

I fixed it by changing the code from doing INSTANCE.[method] with that static variable I defined at the top to instead use kernel32.INSTANCE.[method] .

I figured it out by looking at the definition of kernel32 and noticing it had that static INSTANCE variable.