Question: When does ConcurrentDictionary<TKey, TValue>.TryRemove(TKey, out TValue)

[RenderMichael]

I'm trying to use a concurrent dictionary for thread-safe access, and although it's not the main concern, high performance and low code complexity are something I'm interested in.

Looking at the documentation for ConcurrentDictionary<TKey, TValue>.TryRemove(TKey, out TValue), The comment about the return value is "true if the object was removed successfully; otherwise, false".

What does "removed successfully" mean? Does it mean the key was found, or is it possible for a key to exist while being failed to be removed? It's not inherently clear to me from this phrasing.

Right now I'm being defensive and writing code like this:

internal void Clear(string context)
{
    while (_outputs.ContainsKey(context))
    {
        if (_outputs.TryRemove(context, out StringWriter? writer))
        {
            writer.Dispose();
        }
    }
}

And I want to know if it's still safe to write

internal void Clear(string context)
{
    if (_outputs.TryRemove(context, out StringWriter? writer))
    {
        writer.Dispose();
    }
}

If possible, could the documentation be changed so its more clear to anyone not familiar enough with ConcurrentDictionary<TKey, TValue> internals to know this?

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Issue Details

---

I'm trying to use a concurrent dictionary for thread-safe access, and although it's not the main concern, high performance and low code complexity are something I'm interested in.

Looking at the documentation for ConcurrentDictionary<TKey, TValue>.TryRemove(TKey, out TValue), The comment about the return value is "true if the object was removed successfully; otherwise, false".

What does "removed successfully" mean? Does it mean the key was found, or is it possible for a key to exist while being failed to be removed? It's not inherently clear to me from this phrasing.

Right now I'm being defensive and writing code like this:

internal void Clear(string context)
{
    while (_outputs.ContainsKey(context))
    {
        if (_outputs.TryRemove(context, out StringWriter? writer))
        {
            writer.Dispose();
        }
    }
}

And I want to know if it's still safe to write

internal void Clear(string context)
{
    if (_outputs.TryRemove(context, out StringWriter? writer))
    {
        writer.Dispose();
    }
}

If possible, could the documentation be changed so its more clear to anyone not familiar enough with ConcurrentDictionary<TKey, TValue> internals to know this?

Author:	RenderMichael
Assignees:	-
Labels:	area-System.Collections, untriaged
Milestone:	-

[stephentoub]

If it's found, it'll be removed. (Of course, concurrently someone else could add it back.)

[RenderMichael]

What if it exists but it's not found? The documentation makes it not perfectly clear for me.

Basically what I'm asking is whether the second code block is just as correct as the first code block.

[stephentoub]

If it exists, it'll be found and removed and true will be returned.