Do I need to release the COM object on every 'foreach' iteration?
Here's the (potential) problem:
I create a COM object, an开发者_运维知识库d then use a 'foreach' to iterate through each element in a collection it returns. Do I need to release each individual element I iterate through in the collection? (See code below.) If so, I can't think of a way to effectively to release it from within a 'finally' statement, just in case there is an error as the item is being operated upon.
Any suggestions?
private static void doStuff()
{
ComObjectClass manager = null;
try
{
manager = new ComObjectClass();
foreach (ComObject item in manager.GetCollectionOfItems())
{
Log.Debug(item.Name);
releaseComObject(item); // <-- Do I need this line?
// It isn't in a 'finally' block...
// ...Possible memory leak?
}
}
catch (Exception) { }
finally
{
releaseComObject(manager);
}
}
private static void releaseComObject(object instance)
{
if (instance != null)
{
try
{
System.Runtime.InteropServices.Marshal.ReleaseComObject(instance);
}
catch
{
/* log potential memory leak */
Log.Debug("Potential memory leak: Unable to release COM object.");
}
finally
{
instance = null;
}
}
}
You should not use a foreach
statement with a COM object, as a reference is made behind the scenes to which you have no control over releasing. I would switch to a for
loop and make sure you never use two dots with COM objects.
The way this would look would be:
try
{
manager = new ComObjectClass();
ComObject comObject = null;
ComObject[] collectionOfComItems = manager.GetCollectionOfItems();
try
{
for(int i = 0; i < collectionOfComItems.Count; i++)
{
comObject = collectionOfComItems[i];
ReleaseComObject(comObject);
}
}
finally
{
ReleaseComObject(comObject);
}
}
finally
{
ReleaseComObject(manager);
}
Another way is to create your own iterator function :
IEnumerable<ComObject> GetChildItems(this ComObjectClass manager) {
ComObject comObject = null;
ComObject[] collectionOfComItems = manager.GetCollectionOfItems();
for (int i = 0; i < collectionOfComItems.Length; i++) {
try {
comObject = collectionOfComItems[i];
yield return comObject;
} finally {
if (comObject != null)
Marshal.ReleaseComObject(comObject);
}
}
yield break;
}
private static void doStuff() {
ComObjectClass manager = null;
try {
manager = new ComObjectClass();
foreach (ComObject item in manager.GetChildItems()) {
Log.Debug(item.Name);
}
} finally {
releaseComObject(manager);
}
}
I feel this makes your code much more readable, especially if you need to iterate through the child items at multiple times.
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