FreeBSD/Linux Kernel Cross Reference
sys/iokit/IOKit/IOWorkLoop.h

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    #ifndef __IOKIT_IOWORKLOOP_H
    #define __IOKIT_IOWORKLOOP_H
    
    #include <libkern/c++/OSObject.h>
    #include <IOKit/IOReturn.h>
    #include <IOKit/IOLib.h>
    #include <IOKit/IOLocks.h>
    
    #include <IOKit/system.h>
    
    #if IOKITSTATS
    #include <IOKit/IOStatisticsPrivate.h>
    #endif
    
    class IOEventSource;
    class IOTimerEventSource;
    class IOCommandGate;
    
    /*! @class IOWorkLoop
        @discussion An IOWorkLoop is a thread of control that is intended to be used to provide single threaded access to hardware.  This class has no knowledge of the nature and type of the events that it marshals and forwards.  When a device driver successfully starts (see IOService::start), it is expected to create the event sources it will need to receive events.  Then a work loop is initialized and the events are added to the work loop for monitoring.  In general this set up will be automated by the family superclass of the specific device.
    <br><br>
            The thread main method walks the event source linked list and messages each one requesting a work check.  At this point each event source is expected to notify its registered owner that the event has occurred.  After each event has been walked and each indicates that another loop isn't required (by setting the 'more' flag to false) the thread will go to sleep on a signaling semaphore.
    <br><br>
            When an event source is registered with a work loop it is informed of the semaphore to use to wake up the loop.
    */
    class IOWorkLoop : public OSObject
    {
        OSDeclareDefaultStructors(IOWorkLoop)
    
    public:
    /*!
        @typedef Action
        @discussion Type and arguments of callout C function that is used when
    a runCommand is executed by a client.  Cast to this type when you want a C++
    member function to be used.  Note the arg1 - arg3 parameters are straight pass
    through from the runCommand to the action callout.
        @param target
            Target of the function, can be used as a refcon.  Note if a C++ function
    was specified, this parameter is implicitly the first parameter in the target
    member function's parameter list.
        @param arg0 Argument to action from run operation.
        @param arg1 Argument to action from run operation.
        @param arg2 Argument to action from run operation.
        @param arg3 Argument to action from run operation.
    */
        typedef IOReturn (*Action)(OSObject *target,
                                   void *arg0, void *arg1,
                                   void *arg2, void *arg3);
        enum {
            kPreciousStack = 0x00000001
        };
    
    private:
    /*! @function threadMainContinuation
        @abstract Static function that calls the threadMain function. 
    */
        static void threadMainContinuation(IOWorkLoop *self);
            
    /*! @function eventSourcePerformsWork
            @abstract Checks if the event source passed in overrides checkForWork() to perform any work.
    IOWorkLoop uses this to determine if the event source should be polled in runEventSources() or not.
            @param inEventSource The event source to check.
    */
            bool eventSourcePerformsWork(IOEventSource *inEventSource);
            
    protected:
    
    /*! @typedef maintCommandEnum
        @discussion Enumeration of commands that _maintCommand can deal with.  
        @constant mAddEvent Used to tag a Remove event source command.
        @constant mRemoveEvent Used to tag a Remove event source command. 
   */    
       typedef enum { mAddEvent, mRemoveEvent } maintCommandEnum;
   
   /*! @var gateLock
       Mutual exclusion lock that is used by close and open Gate functions.  
       This is a recursive lock, which allows multiple layers of code to share a single IOWorkLoop without deadlock.  This is common in IOKit since threads of execution tend to follow the service plane in the IORegistry, and multiple objects along the call path may acquire the gate for the same (shared) workloop.
   */
       IORecursiveLock *gateLock;
   
   /*! @var eventChain 
       Pointer to first event source in linked list. 
   */
       IOEventSource *eventChain;
   
   /*! @var controlG 
       Internal control gate to maintain event system.  
   */
       IOCommandGate *controlG;
   
   /*! @var workToDoLock
       The spin lock that is used to guard the 'workToDo' variable. 
   */
       IOSimpleLock *workToDoLock;
   
   /*! @var workThread 
       Work loop thread.   
   */
       IOThread workThread;
   
   /*! @var workToDo
       Used to to indicate that an interrupt has fired and needs to be processed.
   */
       volatile bool workToDo;
   
   /*! @var loopRestart
       Set if an event chain has been changed and the system has to be rechecked from start.  (Internal use only)  
   */
       bool loopRestart;
   
   /*! @struct ExpansionData
       @discussion This structure will be used to expand the capablilties of the IOWorkLoop in the future.
   */    
       struct ExpansionData {
           IOOptionBits options;
           IOEventSource *passiveEventChain;
   #if DEBUG
           void * allocationBacktrace[16];
   #endif /* DEBUG */
   #if IOKITSTATS
           struct IOWorkLoopCounter *counter;
   #else
           void *iokitstatsReserved;
   #endif
       };
   
   /*! @var reserved
       Reserved for future use.  (Internal use only) 
   */
       ExpansionData *reserved;
   
   /*! @function _maintRequest
       @abstract Synchronous implementation of addEventSource and removeEventSource functions. 
       @discussion This function implements the commands as defined in the maintCommandEnum.  It can be subclassed but it isn't an external API in the usual sense.  A subclass implementation of _maintRequest would be called synchronously with respect to the work loop and it should be implemented in the usual way that an ioctl would be.
       @return kIOReturnUnsupported if the command given is not implemented, kIOReturnSuccess otherwise.
   */
       virtual IOReturn _maintRequest(void *command, void *data, void *, void *);
   
   /*! @function free
       @discussion Mandatory free of the object independent of the current retain count.  If the work loop is running, this method will not return until the thread has successfully terminated.  Each event source in the chain will be released and the working semaphore will be destroyed.
   <br><br>
           If the client has some outstanding requests on an event they will never be informed of completion.  If an external thread is blocked on any of the event sources they will be awakened with a KERN_INTERUPTED status. 
   */
       virtual void free();
   
   /*! @function threadMain
       @discussion Work loop threads main function.  This function consists of 3
       loops: the outermost loop is the semaphore clear and wait loop, the middle
       loop terminates when there is no more work, and the inside loop walks the
       event list calling the checkForWork method in each event source.  If an
       event source has more work to do, it can set the more flag and the middle
       loop will repeat.  When no more work is outstanding the outermost will
       sleep until an event is signalled.
   */
       virtual void threadMain();
   
   public:
   
   /*! @function workLoop
       @abstract Factory member function to construct and intialize a work loop.
       @result Returns a workLoop instance if constructed successfully, 0 otherwise. 
   */
       static IOWorkLoop *workLoop();
   
   /*! @function workLoopWithOptions(IOOptionBits options)
       @abstract Factory member function to constuct and intialize a work loop.
       @param options Options - kPreciousStack to avoid stack deallocation on paging path.
       @result Returns a workLoop instance if constructed successfully, 0 otherwise. 
   */
       static IOWorkLoop *workLoopWithOptions(IOOptionBits options);
   
   /*! @function init
       @discussion Initializes an instance of the workloop.  This method creates and initializes the signaling semaphore, the controller gate lock, and spawns the thread that will continue executing.
       @result Returns true if initialized successfully, false otherwise. 
   */
       virtual bool init();
   
   /*! @function getThread
       @abstract Gets the workThread.
       @result Returns workThread.
   */
       virtual IOThread getThread() const;
   
   /*! @function onThread
       @abstract Is the current execution context on the work thread? 
       @result Returns true if IOThreadSelf() == workThread. 
   */
       virtual bool onThread() const;
   
   /*! @function inGate
       @abstract Is the current execution context holding the work-loop's gate? 
       @result Returns true if IOThreadSelf() is gate holder.
   */
       virtual bool inGate() const;
       
   /*! @function addEventSource
       @discussion Add an event source to be monitored by the work loop.  This function does not return until the work loop has acknowledged the arrival of the new event source.  When a new event has been added the threadMain will always restart its loop and check all outstanding events.  The event source is retained by the work loop.
       @param newEvent Pointer to IOEventSource subclass to add.
       @result Always returns kIOReturnSuccess. 
   */
       virtual IOReturn addEventSource(IOEventSource *newEvent);
   
   /*! @function removeEventSource
       @discussion Remove an event source from the work loop.  This function does not return until the work loop has acknowledged the removal of the event source.  When an event has been removed the threadMain will always restart its loop and check all outstanding events.  The event source will be released before return.
       @param toRemove Pointer to IOEventSource subclass to remove.
       @result Returns kIOReturnSuccess if successful, kIOReturnBadArgument if toRemove couldn't be found. 
   */
       virtual IOReturn removeEventSource(IOEventSource *toRemove);
   
   /*! @function enableAllEventSources
       @abstract Calls enable() in all event sources.
       @discussion For all event sources in eventChain, call enable() function.  See IOEventSource::enable().
   */
       virtual void enableAllEventSources() const;
   
   /*! @function disableAllEventSources
       @abstract Calls disable() in all event sources.
       @discussion For all event sources in eventChain, call disable() function.  See IOEventSource::disable().
   */
       virtual void disableAllEventSources() const;
   
   /*! @function enableAllInterrupts
       @abstract Calls enable() in all interrupt event sources.
       @discussion For all event sources (ES) for which OSDynamicCast(IOInterruptEventSource, ES) is valid, in eventChain call enable() function.  See IOEventSource::enable().
   */
       virtual void enableAllInterrupts() const;
   
   /*! @function disableAllInterrupts
       @abstract Calls disable() in all interrupt event sources.
       @discussion For all event sources (ES) for which OSDynamicCast(IOInterruptEventSource, ES) is valid,  in eventChain call disable() function.  See IOEventSource::disable().
   */
       virtual void disableAllInterrupts() const;
   
   
   protected:
       // Internal APIs used by event sources to control the thread
       friend class IOEventSource;
       friend class IOTimerEventSource;
   #if IOKITSTATS
       friend class IOStatistics;
   #endif
       virtual void signalWorkAvailable();
       virtual void openGate();
       virtual void closeGate();
       virtual bool tryCloseGate();
       virtual int  sleepGate(void *event, UInt32 interuptibleType);
       virtual void wakeupGate(void *event, bool oneThread);
   
   public:
       /* methods available in Mac OS X 10.1 or later */
   
   /*! @function runAction
       @abstract Single thread a call to an action with the work-loop.
       @discussion Client function that causes the given action to be called in a single threaded manner.  Beware: the work-loop's gate is recursive and runAction can cause direct or indirect re-entrancy.  When executing on a client's thread, runAction will sleep until the work-loop's gate opens for execution of client actions, the action is single threaded against all other work-loop event sources.
       @param action Pointer to function to be executed in work-loop context.
       @param arg0 Parameter for action parameter, defaults to 0.
       @param arg1 Parameter for action parameter, defaults to 0.
       @param arg2 Parameter for action parameter, defaults to 0.
       @param arg3 Parameter for action parameter, defaults to 0.
       @result Returns the value of the Action callout.
   */
       virtual IOReturn runAction(Action action, OSObject *target,
                                  void *arg0 = 0, void *arg1 = 0,
                                  void *arg2 = 0, void *arg3 = 0);
   
   /*! @function runEventSources
       @discussion Consists of the inner 2 loops of the threadMain function(qv).
       The outer loop terminates when there is no more work, and the inside loop
       walks the event list calling the checkForWork method in each event source.
       If an event source has more work to do, it can set the more flag and the
       outer loop will repeat.
   <br><br>
       This function can be used to clear a priority inversion between the normal
       workloop thread and multimedia's real time threads.  The problem is that
       the interrupt action routine is often held off by high priority threads.
       So if they want to get their data now they will have to call us and ask if
       any data is available.  The multi-media user client will arrange for this
       function to be called, which causes any pending interrupts to be processed
       and the completion routines called.  By the time the function returns all
       outstanding work will have been completed at the real time threads
       priority.
   
       @result Return false if the work loop is shutting down, true otherwise.
   */
       virtual bool runEventSources();
   
   protected:
       // Internal APIs used by event sources to control the thread
       virtual int sleepGate(void *event, AbsoluteTime deadline, UInt32 interuptibleType);
   
   protected:
   #if __LP64__
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 0);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 1);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 2);
   #else
       OSMetaClassDeclareReservedUsed(IOWorkLoop, 0);
       OSMetaClassDeclareReservedUsed(IOWorkLoop, 1);
       OSMetaClassDeclareReservedUsed(IOWorkLoop, 2);
   #endif
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 3);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 4);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 5);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 6);
       OSMetaClassDeclareReservedUnused(IOWorkLoop, 7);
   };
   
   #endif /* !__IOKIT_IOWORKLOOP_H */

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