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IOEventSource

Overview

Abstract class for all work-loop event sources.

Discussion

The IOEventSource declares the abstract super class that all event sources must inherit from if an IOWorkLoop is to receive events from them.

An event source can represent any event that should cause the work loop of a device to wake up and perform work. Two examples of event sources are the IOInterruptEventSource which delivers interrupt notifications and IOCommandGate which delivers command requests.

A kernel module can always use the work-loop model for serializing access to anything at all. The IOEventSource is used for communicating events to the work loop, and the chain of event sources should be used to walk the possible event sources and demultipex them. Note a particular instance of an event source may only be a member of 1 linked list chain. If you need to move it between chains than make sure it is removed from the original chain before attempting to move it.

The IOEventSource makes no attempt to maintain the consistency of its internal data across multi-threading. It is assumed that the user of these basic tools will protect the data that these objects represent in some sort of device wide instance lock. For example, the IOWorkLoop maintains the event chain by handing off change request to its own thread and thus single threading access to its state.

All subclasses of the IOEventSource are expected to implement the checkForWork() member function.

checkForWork() is the key method in this class. It is called by some work loop when convienient and is expected to evaluate its internal state and determine if an event has occurred since the last call. In the case of an event having occurred then the instance defined target(owner)/action will be called. The action is stored as an ordinary C function pointer but the first parameter is always the owner. This means that a C++ member function can be used as an action function though this depends on the ABI.

Although the eventChainNext variable contains a reference to the next event source in the chain this reference is not retained. The list 'owner' i.e. the client that creates the event, not the work loop, is expected to retain the source.

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Functions

checkForWork

Pure Virtual member function used by IOWorkLoop for work scheduling.

disable

Disables event source.

enable

Enables event source.

getAction

Get'ter for action variable.

getNext

Get'ter for eventChainNext variable.

getWorkLoop

Get'ter for workLoop variable.

init

Primary initializer for the IOEventSource class.

isEnabled

Get'ter for enable variable.

onThread

Convenience function for workLoop->onThread.

setAction

Set'ter for action variable.

setNext

Set'ter for eventChainNext variable.

setWorkLoop

Set'ter for workLoop variable.

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checkForWork

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Pure Virtual member function used by IOWorkLoop for work scheduling.

protected

virtual bool checkForWork() = 0; 

Return Value

Returns true if this function needs to be called again before all its outstanding events have been processed.

Discussion

This function will be called to request a subclass to check its internal state for any work to do and then to call out the owner/action.

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disable

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Disables event source.

public

virtual void disable(); 

Discussion

A subclass implementation is expected to respect the enabled state when checkForWork is called.

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enable

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Enables event source.

public

virtual void enable(); 

Discussion

A subclass implementation is expected to respect the enabled state when checkForWork is called. Calling this function will cause the work loop to be signalled so that a checkForWork is performed.

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getAction

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Get'ter for action variable.

public

virtual IOEventSource::Action getAction() const; 

Return Value

Returns the value of action.

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getNext

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Get'ter for eventChainNext variable.

protected

virtual IOEventSource *getNext() const; 

Return Value

Returns the value of eventChainNext.

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getWorkLoop

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Get'ter for workLoop variable.

public

virtual IOWorkLoop *getWorkLoop() const; 

Return Value

Returns the value of workLoop.

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init

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Primary initializer for the IOEventSource class.

protected

virtual bool init(
    OSObject *owner,
    IOEventSource::Action action = 0); 

Parameters

owner

Owner of this instance of an event source. Used as the first parameter of the action callout. Owner will generally be an OSObject it doesn't have to be as no member functions will be called directly in it. It can just be a refcon for a client routine.

action

Pointer to C call out function. Action is a pointer to a C function that gets called when this event source has outstanding work. It will usually be called by the checkForWork member function. The first parameter of the action call out will always be the owner, this allows C++ member functions to be used as actions. Defaults to 0.

Return Value

Returns true if the inherited classes and this instance initialize successfully.

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isEnabled

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Get'ter for enable variable.

public

virtual bool isEnabled() const; 

Return Value

Returns true if enabled.

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onThread

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Convenience function for workLoop->onThread.

public

virtual bool onThread() const; 

Return Value

Returns true if called on the work loop thread.

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setAction

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Set'ter for action variable.

public

virtual void setAction(
    IOEventSource::Action action); 

Parameters

action

Pointer to a C function of type IOEventSource::Action.

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setNext

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Set'ter for eventChainNext variable.

protected

virtual void setNext(
    IOEventSource *next); 

Parameters

next

Pointer to another IOEventSource instance.

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setWorkLoop

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Set'ter for workLoop variable.

protected

virtual void setWorkLoop(
    IOWorkLoop *workLoop); 

Parameters

workLoop

Target work loop of this event source instance. A subclass of IOWorkLoop that at least reacts to signalWorkAvailable() and onThread functions.

Typedefs

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Action

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public

typedef void ( *Action)(
    OSObject *owner,
    ...); 

Fields

owner

Target of the function, can be used as a refcon. The owner is set during initialization. Note if a C++ function was specified this parameter is implicitly the first paramter in the target member function's parameter list.

Discussion

Placeholder type for C++ function overloading discrimination. As the all event sources require an action and it has to be stored somewhere and be of some type, this is that type.

Structs and Unions

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ExpansionData

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protected

struct ExpansionData {
}; 

Discussion

This structure will be used to expand the capablilties of the IOEventSource in the future.

Member Data

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action

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protected

Action action; 

Discussion

The action method called when an event has been delivered

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enabled

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protected

bool enabled; 

Discussion

Is this event source enabled to deliver requests to the work-loop.

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eventChainNext

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protected

IOEventSource *eventChainNext; 

Discussion

The next event source in the event chain. nil at end of chain.

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owner

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protected

OSObject *owner; 

Discussion

The owner object called when an event has been delivered.

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refcon

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protected

void *refcon; 

Discussion

Whatever the client wants to do.

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reserved

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protected

ExpansionData *reserved; 

Discussion

Reserved for future use. (Internal use only)

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workLoop

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protected

IOWorkLoop *workLoop; 

Discussion

What is the work-loop for this event source.

#defines

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IOEventSourceAction

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#define IOEventSourceAction IOEventSource::Action 

Discussion

Backward compatibilty define for the old non-class scoped type definition. See Action.

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Last Updated: 2008-12-19