time_queue v0.9.0 TimeQueue.GbTrees

Implements a timers queue based on gb_trees.

The queue keys are a two-tuple composed of the timestamp of an event and an unique integer.

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 keep 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 restart.

The main drawback is that the queue entries must be manually checked for expired timers.

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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.

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.

peek_entry(tq) deprecated

Alias for peek_event/1.

Alias for peek_event/2.

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.

pop_entry(tq) deprecated

Alias for pop_event/1.

Alias for pop_event/2.

Extracts the next event of the queue with the current system time as now/0.

Extracts the next event of the queue according to the given current time in milliseconds.

Returns the numer of entries in the queue.

Returns the time reference of an queue event. This reference is used as a key to identify a unique event.

Returns the value of an queue event.

Link to this section Types

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enqueue_return()

enqueue_return() :: {:ok, tref(), t()}
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event()

(opaque)
event()
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event_value()

event_value() :: any()
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id()

(opaque)
id()
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peek_event_return()

peek_event_return() ::
  :empty | {:delay, tref(), non_neg_integer()} | {:ok, event()}
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peek_return()

peek_return() ::
  :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value()}
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pop_event_return()

pop_event_return() ::
  :empty | {:delay, tref(), non_neg_integer()} | {:ok, event(), t()}
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pop_return()

pop_return() ::
  :empty | {:delay, tref(), non_neg_integer()} | {:ok, event_value(), t()}
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t()

(opaque)
t()
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timespec()

timespec() :: {pos_integer(), timespec_unit()}
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timespec_unit()

timespec_unit() ::
  :ms
  | :second
  | :seconds
  | :minute
  | :minutes
  | :hour
  | :hours
  | :day
  | :days
  | :week
  | :weeks
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timestamp_ms()

timestamp_ms() :: pos_integer()
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tref()

(opaque)
tref()
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ttl()

ttl() :: timespec() | integer()

Link to this section Functions

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delete(tq, tref)

delete(t(), event() | tref()) :: t()

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.

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delete_val(tq, unwanted)

delete_val(t(), any()) :: t()

Deletes all entries from the queue whose values are equal to unwanted.

This function is slow with gb_trees, see filter/2.

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enqueue(tq, ttl, val)

enqueue(t(), ttl(), any()) :: enqueue_return()

Adds a new event to the queue with a TTL and the current system time as now/0.

See enqueue/4.

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enqueue(tq, ttl, val, now_ms)

enqueue(t(), ttl(), any(), now :: integer()) :: enqueue_return()

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.

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enqueue_abs(arg, ts, val)

enqueue_abs(t(), end_time :: integer(), value :: any()) :: enqueue_return()

Adds a new event to the queue with an absolute timestamp.

Returns {:ok, tref, new_queue} where tref is a timer reference.

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filter(arg, fun)

filter(t(), (event() -> bool())) :: t()

Returns a new queue with entries for whom the given callback returned a truthy value.

With the gbtrees implementation, this operation is _very expensive as we convert the tree to and ordered list, filter the list, and convert back to a tree.

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filter_val(tq, fun)

filter_val(t(), (any() -> bool())) :: t()

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.

This function is slow with gb_trees, see filter/2.

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new()

new() :: t()

Creates an empty time queue.

iex> tq = TimeQueue.GbTrees.new()
iex> TimeQueue.GbTrees.peek_event(tq)
:empty
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peek(tq)

peek(t()) :: peek_return()

Returns the next value of the queue or a delay in milliseconds before the next value.

See peek/2.

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peek(tq, now)

peek(t(), now_ms :: timestamp_ms()) :: peek_return()

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}.

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peek_entry(tq)

peek_entry(t()) :: peek_event_return()
This function is deprecated. Use peek_event/1 instead.

Alias for peek_event/1.

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peek_entry(tq, now_ms)

peek_entry(t(), now_ms :: timestamp_ms()) :: peek_event_return()
This function is deprecated. Use peek_event/2 instead.

Alias for peek_event/2.

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peek_event(tq)

peek_event(t()) :: peek_event_return()

Returns the next event of the queue or a delay in milliseconds before the next value.

event values can be retrieved with TimeQueue.GbTrees.value/1.

See peek_event/2.

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peek_event(arg, now)

peek_event(t(), now_ms :: timestamp_ms()) :: peek_event_return()

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

iex> {:ok, tref, tq} = TimeQueue.GbTrees.new() |> TimeQueue.GbTrees.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.GbTrees.peek_event(tq, _now = 20)
iex> {:ok, _} = TimeQueue.GbTrees.peek_event(tq, _now = 100)

Extracts the next event in the queue or returns a delay.

See pop/2.

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pop(tq, now)

pop(t(), now_ms :: timestamp_ms()) :: pop_return()

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 from new_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

iex> {:ok, tref, tq} = TimeQueue.GbTrees.new() |> TimeQueue.GbTrees.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.GbTrees.pop(tq, _now = 20)
iex> {:ok, value, _} = TimeQueue.GbTrees.pop(tq, _now = 100)
iex> value
:hello
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pop_entry(tq)

pop_entry(t()) :: pop_event_return()
This function is deprecated. Use pop_event/1 instead.

Alias for pop_event/1.

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pop_entry(tq, now_ms)

pop_entry(t(), now_ms :: timestamp_ms()) :: pop_event_return()
This function is deprecated. Use pop_event/2 instead.

Alias for pop_event/2.

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pop_event(tq)

pop_event(t()) :: pop_event_return()

Extracts the next event of the queue with the current system time as now/0.

See pop_event/2.

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pop_event(arg, now)

pop_event(t(), now_ms :: timestamp_ms()) :: pop_event_return()

Extracts the next event of 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 from new_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

iex> {:ok, tref, tq} = TimeQueue.GbTrees.new() |> TimeQueue.GbTrees.enqueue(100, :hello, _now = 0)
iex> {:delay, ^tref, 80} = TimeQueue.GbTrees.pop_event(tq, _now = 20)
iex> {:ok, _, _} = TimeQueue.GbTrees.pop_event(tq, _now = 100)
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size(arg)

size(t()) :: integer()

Returns the numer of entries in the queue.

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tref(arg)

tref(event()) :: any()

Returns the time reference of an queue event. This reference is used as a key to identify a unique event.

iex> tq = TimeQueue.GbTrees.new()
iex> {:ok, tref, tq} = TimeQueue.GbTrees.enqueue(tq, 10, :my_value)
iex> Process.sleep(10)
iex> {:ok, event} = TimeQueue.GbTrees.peek_event(tq)
iex> tref == TimeQueue.GbTrees.tref(event)
true
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value(arg)

value(event()) :: any()

Returns the value of an queue event.

iex> tq = TimeQueue.GbTrees.new()
iex> {:ok, _, tq} = TimeQueue.GbTrees.enqueue(tq, 10, :my_value)
iex> Process.sleep(10)
iex> {:ok, event} = TimeQueue.GbTrees.peek_event(tq)
iex> TimeQueue.GbTrees.value(event)
:my_value