safearrayreleasetest.java

java 与COM组件的连接桥

package com.jacob.test.safearray;

import com.jacob.com.ComThread;
import com.jacob.com.SafeArray;
import com.jacob.com.Variant;

/**
 * <p>
 * May need to run with some command line options (including from inside Eclipse).  
 * Look in the docs area at the Jacob usage document for command line options.
 *  <p>
 * SF 1085370
	In my understatnding, an instance of SafeArray java
	class has a
	value of a pointer to VARIANT structure that contains a
	pointer to
	a SAFEARRAY strucuture.
	
	On the other hand, we can create a Variant object from
	the
	SafeArray object like this:
	SafeArray sa = ...;
	Variant val = new Variant(sa);
	the val object has a pointer to another VARIANT
	structure that
	contains a pointer to the same SAFEARRAY structure.
	
	In this case, the val object has a pointer to another
	VARIANT that
	contains a pointer to the same SAFEARRAY like this:
	
	+-----------+
	|SafeArray  | +------------+ 
	| m_pV--->VARIANT(a) |
	+-----------+ | VT_ARRAY| +---------+
	| parray---->SAFEARRAY|
	+------------+ +^--------+
	|
	+-----------+ |
	|Variant    | +------------+ |
	| m_pVariant--->VARIANT(b) | |
	+-----------+ | VT_ARRAY| |
	| parray-----+
	+------------+
	
	When previous objects are rereased by
	ComThread.Release(),
	first the VARIANT(a) is released by VariantClear()
	function,
	and second the VARIANT(b) is released by VariantClear()
	function too.
	But the SAFEARRAY was already released by the
	VARIANT(a).
	
	So, in my enviroment (WinXP + J2SDK 1.4.1) the
	following java program
	is sometimes crash with EXCEPTION_ACCESS_VIOLATION.

	
	To solve this problem, it is nessesary to copy the
	SAFEARRAY like this:
	
	+-----------+
	|Variant | +------------+
	| m_pVariant--->VARIANT(a) |
	+-----------+ | VT_ARRAY| +---------+
	| parray---->SAFEARRAY|
	+------------+ +|--------+
	|
	+-----------+ | copySA()
	|SafeArray | +------------+ |
	| m_pV--->VARIANT(b) | V
	+-----------+ | VT_ARRAY| +---------+
	| parray---->SAFEARRAY|
	+------------+ +---------+
 */

public class SafeArrayReleaseTest 
{
    final static int MAX = 300; 
    public static void main(String[] args) 
    {
        int count;
        System.out.println("Starting test for max = "+MAX);
        for(count = 1; count<MAX; count++)
        {
            int i = 0;
            try 
            {
                ComThread.InitMTA();
                for (i = 0; i < count; i++) 
                {
                    SafeArray a1 = new SafeArray(Variant.VariantVariant, 2);
                    a1.setVariant(0, new Variant("foo"));
                    a1.setVariant(1, new Variant("bar"));
                    Variant v = new Variant(a1);
                    SafeArray a2 = v.toSafeArray(true);
                    if (a2 == null){
                    	System.out.println("got null back from toSafeArray()");
                    }
                }
                ComThread.Release();
                System.gc();
                //System.out.print(".");
            } 
            catch (Exception e) 
            {
                System.out.println("\nTest fails with i = " + i + " (max = "+MAX+")");
                e.printStackTrace();
                break;
            }
        }
        System.gc();
        System.out.println("\nTest ends with count = " + count + " (max = "+MAX+")");
    }
}