View Source TimeQueue (time_queue v1.1.1)
Implements a timers queue based on a list of maps. The queue can be encoded as JSON.
The performance will be worse for large queues in regard to the previous gb_trees based implementation, although the difference is negligible for small queues (<= 1000 entries).
All map keys are shrinked to a single letter as this queue is intended to be encoded and published to HTTP clients over the wire, mutiple times.
The queue keys are a map composed of the timestamp (t
) of an event
and an unique integer (u
).
No erlang timers or processes are used, as the queue is only a data structure. The advantage is that the queue can be persisted on storage and keeps working after restarting the runtime. The queue maintain its own list of unique integers to avoir relying on BEAM unique integers as they are reset on VM restarts.
The main drawback of a functional queue is that the queue entries must be manually checked for expired timers.
Link to this section Summary
Functions
Deletes an event from the queue and returns the new queue.
Deletes all entries from the queue whose values are equal to unwanted
.
Adds a new event to the queue with a TTL and the current system time as now/0
.
Adds a new event to the queue with a TTL relative to the given timestamp in milliseconds.
Adds a new event to the queue with an absolute timestamp.
Returns a new queue with entries for whom the given callback returned a truthy value.
Returns a new queue with entries for whom the given callback returned a truthy value.
Creates an empty time queue.
This function is used internally to determine the current time when using
functions enqueue/3
, pop/1
, pop_event/1
and peek_event/1
.
Returns the next value of the queue or a delay in milliseconds before the next value.
Returns the next value of the queue, or a delay, according to the given current time in milliseconds.
Returns the next event of the queue or a delay in milliseconds before the next value.
Returns the next event of the queue according to the given current time in milliseconds.
Extracts the next event in the queue or returns a delay.
Extracts the next event in the queue according to the given current time in milliseconds.
Extracts the next event in the queue with the current system time as now/0
.
Extracts the next event in the queue according to the given current time in milliseconds.
Returns the number of entries in the queue.
Returns the time to next event.
Returns the time to next event.
Provides a GenServer
compatible timeout from the queue, giving the time to
the next event.
Returns the absolute timestamp a queue event is scheduled for.
Returns the time reference of a queue event. This reference is used as a key to identify a unique event.
Returns the value of a queue event.
Link to this section Types
@opaque event()
@type event_value() :: any()
@opaque t()
@type timespec() :: {pos_integer(), timespec_unit()}
@type timespec_unit() ::
:ms
| :second
| :seconds
| :minute
| :minutes
| :hour
| :hours
| :day
| :days
| :week
| :weeks
@type timestamp_ms() :: pos_integer()
@opaque tref()
Link to this section Functions
Deletes an event from the queue and returns the new queue.
It accepts a time reference or a full event. When an event is given, its time reference will be used to find the event to delete, meaning the queue event will be deleted even if the value of the passed event was tampered.
The function does not fail if the event cannot be found and simply returns the queue as-is.
Deletes all entries from the queue whose values are equal to unwanted
.
Adds a new event to the queue with a TTL and the current system time as now/0
.
See enqueue/4
.
Adds a new event to the queue with a TTL relative to the given timestamp in milliseconds.
Returns {:ok, tref, new_queue}
where tref
is a timer reference.
Adds a new event to the queue with an absolute timestamp.
Returns {:ok, tref, new_queue}
where tref
is a timer reference.
Returns a new queue with entries for whom the given callback returned a truthy value.
Use filter_val/2
to filter only using values.
Returns a new queue with entries for whom the given callback returned a truthy value.
Unlinke filter/2
, the callback is only passed the event value.
@spec new() :: t()
Creates an empty time queue.
iex> tq = TimeQueue.new()
iex> TimeQueue.peek_event(tq)
:empty
@spec now() :: integer()
This function is used internally to determine the current time when using
functions enqueue/3
, pop/1
, pop_event/1
and peek_event/1
.
It is a simple alias to :erlang.system_time(:millisecond)
. TimeQueue does
not use monotonic time since it already manages its own unique identifiers for
queue entries.
@spec peek(t()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value()}
Returns the next value of the queue or a delay in milliseconds before the next value.
See peek/2
.
@spec peek(t(), now :: timestamp_ms()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value()}
Returns the next value of the queue, or a delay, according to the given current time in milliseconds.
Just like pop/2
vs. pop_event/2
, peek
wil only return {:ok, value}
when a timeout is reached whereas peek_event
will return {:ok, event}
.
@spec peek_event(t()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event()}
Returns the next event of the queue or a delay in milliseconds before the next value.
event values can be retrieved with TimeQueue.value/1
.
See peek_event/2
.
@spec peek_event(t(), now :: timestamp_ms()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event()}
Returns the next event of the queue according to the given current time in milliseconds.
Possible return values are:
:empty
{:ok, event}
if the timestamp of the first event is<=
to the given current time.{:delay, tref, ms}
if the timestamp of the first event is>
to the given current time. The remaining amount of milliseconds is returned.
example
Example
iex> {:ok, tref, tq} = TimeQueue.new() |> TimeQueue.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.peek_event(tq, _now = 20)
iex> {:ok, _} = TimeQueue.peek_event(tq, _now = 100)
@spec pop(t()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value(), t()}
Extracts the next event in the queue or returns a delay.
See pop/2
.
@spec pop(t(), now :: timestamp_ms()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value(), t()}
Extracts the next event in the queue according to the given current time in milliseconds.
Much like pop_event/2
but the tuple returned when an event time is reached
(returns with :ok
) success will only contain the value inserted in the
queue.
Possible return values are:
:empty
{:ok, value, new_queue}
if the timestamp of the first event is<=
to the given current time. The event is deleted fromnew_queue
.{:delay, tref, ms}
if the timestamp of the first event is>
to the given current time. The remaining amount of milliseconds is returned.
example
Example
iex> {:ok, tref, tq} = TimeQueue.new() |> TimeQueue.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.pop(tq, _now = 20)
iex> {:ok, value, _} = TimeQueue.pop(tq, _now = 100)
iex> value
:hello
@spec pop_event(t()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event(), t()}
Extracts the next event in the queue with the current system time as now/0
.
See pop_event/2
.
@spec pop_event(t(), now :: timestamp_ms()) :: :empty | {:delay, tref(), non_neg_integer()} | {:ok, event(), t()}
Extracts the next event in the queue according to the given current time in milliseconds.
Possible return values are:
:empty
{:ok, event, new_queue}
if the timestamp of the first event is<=
to the given current time. The event is deleted fromnew_queue
.{:delay, tref, ms}
if the timestamp of the first event is>
to the given current time. The remaining amount of milliseconds is returned.
example
Example
iex> {:ok, tref, tq} = TimeQueue.new() |> TimeQueue.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.pop_event(tq, _now = 20)
iex> {:ok, event, _} = TimeQueue.pop_event(tq, _now = 100)
iex> TimeQueue.value(event)
:hello
Returns the number of entries in the queue.
Returns the time to next event.
Same as timeout(tq, :infinity, now())
. See timeout/3
.
Returns the time to next event.
Accepts either the current time or an atom to return when the queue is empty.
- If an integer is given, it will has the same result as
timeout(tq, :infinity, integer)
. - If an atom is given, it will has the same result as
timeout(tq, atom, now())
.
See timeout/3
.
@spec timeout(t(), :infinity | :hibernate | atom(), now :: timestamp_ms()) :: non_neg_integer() | :infinity | :hibernate | atom()
Provides a GenServer
compatible timeout from the queue, giving the time to
the next event.
Accepts the current time as a third argument or will default to the current system time.
Returns:
if_empty
when the queue is empty. A common value in that case is either:infinity
or:hibernate
.0
when there the next event time has been reached.- The delay to the next event otherwise.
For instance, when used in a GenServer
, this function can tell when to
automatically wakeup the process.
def handle_call(request, _from, state) do
state = do_stuff(state, request)
timeout = TimeQueue.timeout(state.time_queue)
{:reply, :ok, state, timeout}
end
By default, timeout/1
and timeout/2
(if called with an integer for the
current time) will return :infinity
if the queue if empty. But you may
pass :hibernate
as the second argument for timeout/2
or timeout/3
to
return :hibernate
instead.
Note that any other atom than :infinity
or :hibernate
will be returned
as-is if as well if the queue is empty.
@spec timestamp(event()) :: pos_integer()
Returns the absolute timestamp a queue event is scheduled for.
iex> tq = TimeQueue.new()
iex> {:ok, _, tq} = TimeQueue.enqueue_abs(tq, 1234, :my_value)
iex> {:ok, event} = TimeQueue.peek_event(tq)
iex> TimeQueue.timestamp(event)
1234
Returns the time reference of a queue event. This reference is used as a key to identify a unique event.
iex> tq = TimeQueue.new()
iex> {:ok, tref, tq} = TimeQueue.enqueue(tq, 10, :my_value)
iex> Process.sleep(10)
iex> {:ok, event} = TimeQueue.peek_event(tq)
iex> tref == TimeQueue.tref(event)
true
Returns the value of a queue event.
iex> tq = TimeQueue.new()
iex> {:ok, _, tq} = TimeQueue.enqueue(tq, 10, :my_value)
iex> Process.sleep(10)
iex> {:ok, event} = TimeQueue.peek_event(tq)
iex> TimeQueue.value(event)
:my_value