For example I have var linkedList = new LinkedList<int>();
Then I add one node. linkedList.AddLast(1);
After that I have two threads respectively calling linkedList.AddLast(2); (same statement).
So can I safely expect it becomes 1->2->2 linked list?
Or it can become 1->2 when race condition happens?
(Maybe it also has visibility issue, but before that I firstly wonder if such race condition can happen.)
This is a question that can easily be answered with a quick little test app. The answer is 1->2 will happen sometimes.
private static void RunTest()
{
for (int i = 0; i < 100; i++)
{
var lst = new LinkedList<int>();
Parallel.For(1, 51, j =>
{
lst.AddLast(j);
});
if (lst.Count < 50)
{
Console.WriteLine(lst.Count);
}
}
}
As has been mentioned, this collection is not thread-safe. You will need to serialize the access or use a built-in thread-safe collection.
So can I safely expect it becomes 1->2->2 linked list?
No, you can't. LinkedList<T> is not thread safe.
From MSDN:
This type is not thread safe. If the LinkedList needs to be accessed by multiple threads, you will need to implement their own synchronization mechanism. A LinkedList can support multiple readers concurrently, as long as the collection is not modified. Even so, enumerating through a collection is intrinsically not a thread-safe procedure.
Stephan Toub in one of his answers says:
A ConcurrentLinkedList was originally introduced in preview and beta releases of .NET 4, but it was subsequently removed prior to .NET 4 RTM because the type imposed a rigid programming model and its performance benefits over just locking on access to a linked list weren't significant enough for the primary scenarios to warrant the type's inclusion.
You may implement your own safe LinkedList<T> with a simple locking mechanism around critical sections.
You can't use LinkedList right-away for multi-threading as it is not a thread safe collection. See how make it thread safe or suggest to choose one of thread safe collections.
From MSDN: This type is not thread safe. If the LinkedList needs to be accessed by multiple threads, you will need to implement their own synchronization mechanism.
