An amount of tokens

A configuration for TokenLimiter

A type synonym for a number of "monotonic time" nanoseconds.

This only exists because it is also a Word64 and would be too easy to confuse with a Count.

A token bucket-based rate limiter

This token limiter is thread-safe and guarantees that:

• There will be no thundering herd problem
• Fairness: Waiting processes will be serviced in a first-come first-service order.

Make a token limiter

The initial number of tokens will be the minimum of the tokenLimitConfigInitialTokens and the tokenLimitConfigMaxTokens,

Check if we can debit a number of tokens, and do it if possible.

The returned boolean represents whether the tokens were debited.

Note that there is a small race-condition in which tryDebit sometimes returns False eventhough it could (maybe) have debited because another thread was currently waitDebit-ing without actually waiting (because it didn't need to wait).

Wait until the given number of tokens can be debited.

Returns the time waited, for stats recording purposes.

Note: only reports the time waited due to rate-limiting this specific action, not the wall-clock time waited (that might include waiting for previous actions limited by this rate limiter to finish).

Note: debitor threads are serviced in FIFO order, so a request for a small (and currently satisfiable) number of tokens can still be delayed by a debit request for a larger amount of tokens.

Note: the wait time reported can be inflated due to scheduling inaccuracy. See https://gitlab.haskell.org/ghc/ghc/-/issues/16601.

Compute the current number of tokens in a bucket purely.

You should not need this function.