folly::HHWheelTimerBase

Synopsis

Declared in <folly/io/async/HHWheelTimer.h>

template<class Duration>
class HHWheelTimerBase
    : public folly::DelayedDestruction

Description

We model timers as the number of ticks until the next due event. We allow 32-bits of space to track this due interval, and break that into 4 regions of 8 bits. Each region indexes into a bucket of 256 lists.

Bucket 0 represents those events that are due the soonest. Each tick causes us to look at the next list in a bucket. The 0th list in a bucket is special; it means that it is time to flush the timers from the next higher bucket and schedule them into a different bucket.

This technique results in a very cheap mechanism for maintaining time and timers.

Unlike the original timer wheel paper, this implementation does not tick constantly, and instead calculates the exact next wakeup time.

Base Classes

Name	Description
`folly::DelayedDestruction`	DelayedDestruction is a helper class to ensure objects are not deleted while they still have functions executing in a higher stack frame.

Types

Name	Description
`Callback`	A callback to be notified when a timeout has expired.
`Destructor`	Helper class to allow DelayedDestruction classes to be used with std::shared_ptr.
`DestructorGuard`	Classes should create a DestructorGuard object on the stack in any function that may invoke callback functions.
`IntrusivePtr`	This smart pointer is a convenient way to manage a concrete DelayedDestructorBase child. It can replace the equivalent raw pointer and provide automatic memory management.

Type Aliases

Name	Description
`SharedPtr`	Shared pointer to a timer.
`UniquePtr`	Unique pointer that destroys the timer via DelayedDestruction.

Member Functions

Name	Description
`HHWheelTimerBase` [constructor]	Create a new HHWheelTimerBase with the specified interval and the default timeout value set.
`operator=` [deleted]	Deleted copy assignment operator.
`cancelAll`	Cancel all outstanding timeouts
`count`	Return the number of currently pending timeouts
`destroy` [virtual]	destroy() requests destruction of the object.
`getDefaultTimeout`	Get the default timeout interval for this HHWheelTimerBase.
`getDestroyPending`	Returns whether destruction has been requested but deferred.
`getTickInterval`	Get the tick interval for this HHWheelTimerBase.
`isDetachable`	Returns whether the timer can be detached from its event base.
`scheduleTimeout`	`scheduleTimeout` overloads
`scheduleTimeoutFn`	Schedule a callable to be invoked after the specified timeout interval.
`setDefaultTimeout`	Set the default timeout interval for this HHWheelTimerBase.

Static Member Functions

Name	Description
`newTimer`	Creates a new timer wrapped in a UniquePtr.

Static Data Members

Name	Description
`DEFAULT_TICK_INTERVAL`	Default tick interval, in the timer's duration units.

Using Declarations

Name	Description
`attachEventBase`	Attaches the timer to an EventBase.
`detachEventBase`	Detaches the timer from its EventBase.
`getTimeoutManager`	Returns the TimeoutManager driving the timer.

Protected Member Functions

Name	Description
`~HHWheelTimerBase` [destructor] [virtual]	Protected destructor.
`getDestructorGuardCount`	Get the number of DestructorGuards currently protecting this object.
`onDelayedDestroy` [virtual]	Implement onDelayedDestroy in subclasses. onDelayedDestroy() is invoked when the object is potentially being destroyed.

Specializations

Name
`HHWheelTimerBase<std::chrono::microseconds>`
`HHWheelTimerBase<std::chrono::milliseconds>`