attempt v0.2.0 Attempt.Bucket.Token
Implementation of a Token Bucket
A token bucket provides a form of rate limiting
This implmentation is designed to allow for both synchronous and asynchronous token requests. The intent is to simplify the higher level APIs by giving them a soft guarantee of token return.
Since the implementation uses timers (via Process.send_after/3) neither the timing precision not the minimum time window are likely to be useful for all applications.
The primary purpose of this token bucket is to support “longer liver” functions such as 3rd party API calls and calls to other external services like databases.
Implementation
A bucket is defined to hold a maximum number of tokens
The token count is reduced by each call to
get_token/2
When the token count reaches 0, the request is placed in a queue.
Every
:increment_every
milliseconds a new token is created. The increment is calculated as therefill_every / bucket_size
so that the number of tokens is added in time consistent manner.When the timer is reached and a new token is added the pending queue is processed
Link to this section Summary
Functions
Invoked when the server is started. start_link/3
or start/3
will
block until it returns
Link to this section Functions
Invoked when the server is started. start_link/3
or start/3
will
block until it returns.
args
is the argument term (second argument) passed to start_link/3
.
Returning {:ok, state}
will cause start_link/3
to return
{:ok, pid}
and the process to enter its loop.
Returning {:ok, state, timeout}
is similar to {:ok, state}
except handle_info(:timeout, state)
will be called after timeout
milliseconds if no messages are received within the timeout.
Returning {:ok, state, :hibernate}
is similar to
{:ok, state}
except the process is hibernated before entering the loop. See
c:handle_call/3
for more information on hibernation.
Returning :ignore
will cause start_link/3
to return :ignore
and the
process will exit normally without entering the loop or calling c:terminate/2
.
If used when part of a supervision tree the parent supervisor will not fail
to start nor immediately try to restart the GenServer
. The remainder of the
supervision tree will be (re)started and so the GenServer
should not be
required by other processes. It can be started later with
Supervisor.restart_child/2
as the child specification is saved in the parent
supervisor. The main use cases for this are:
- The
GenServer
is disabled by configuration but might be enabled later. - An error occurred and it will be handled by a different mechanism than the
Supervisor
. Likely this approach involves callingSupervisor.restart_child/2
after a delay to attempt a restart.
Returning {:stop, reason}
will cause start_link/3
to return
{:error, reason}
and the process to exit with reason reason
without
entering the loop or calling c:terminate/2
.
Callback implementation for GenServer.init/1
.