Source to iokit/IOKit/IOCommandGate.h

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/*[
    1999-8-10	Godfrey van der Linden(gvdl)
	Created.
]*/
/*! @language embedded-c++ */

#ifndef _IOKIT_IOCOMMANDGATE_H
#define _IOKIT_IOCOMMANDGATE_H

#include <IOKit/IOEventSource.h>

/*!
    @class IOCommandGate : public IOEventSource
    @abstract Single-threaded work-loop client request mechanism.
    @discussion An IOCommandGate instance is an extremely light way mechanism
that executes an action on the driver's work-loop.  'On the work-loop' is
actually a lie but the work-loop single threaded semantic is maintained for this
event source.  Using the work-loop gate rather than execution by the workloop.
The command gate tests for a potential self dead lock by checking if the
runCommand request is made from the work-loop's thread, it doens't check for a
mutual dead lock though where a pair of work loop's dead lock each other.
<br><br>
	The IOCommandGate is a lighter weight version of the IOCommandQueue and
should be used in preference.  Generally use a command queue whenever you need a
client to submit a request to a work loop.  A typical command gate action would
check if the hardware is active, if so it will add the request to a pending
queue internal to the device or the device's family.  Otherwise if the hardware
is inactive then this request can be acted upon immediately.
<br><br>
	CAUTION: The runAction and runCommand functions can not be called from an interrupt context.

*/
class IOCommandGate : public IOEventSource
{
    OSDeclareDefaultStructors(IOCommandGate)

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 owner
	Target of the function, can be used as a refcon.  The owner is set
during initialisation of the IOCommandGate instance.	 Note if a C++ function
was specified this parameter is implicitly the first paramter 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 *owner,
			       void *arg0, void *arg1,
			       void *arg2, void *arg3);

protected:
/*!
    @function checkForWork
    @abstract Not used, $link IOEventSource::checkForWork(). */
    virtual bool checkForWork();

public:
/*! @function commandGate
    @abstract Factory method to create and initialise an IOCommandGate, See $link init.
    @result Returns a pointer to the new command gate if sucessful, 0 otherwise. */
    static IOCommandGate *commandGate(OSObject *owner, Action action = 0);

/*! @function init
    @abstract Class initialiser.
    @discussion Initialiser for IOCommandGate operates only on newly 'newed'
objects.  Shouldn't be used to re-init an existing instance.
    @param owner 	Owner of this, newly created, instance of the IOCommandGate.  This argument will be used as the first parameter in the action callout.
    @param action
	Pointer to a C function that is called whenever a client of the
IOCommandGate calls runCommand.	 NB Can be a C++ member function but caller
must cast the member function to $link IOCommandGate::Action and they will get a
compiler warning.  Defaults to zero, see $link IOEventSource::setAction.
    @result True if inherited classes initialise successfully. */
    virtual bool init(OSObject *owner, Action action = 0);

/*! @function runCommand
    @abstract Single thread a command with the target work-loop.
    @discussion Client function that causes the current action to be called in
a single threaded manner.  Beware the work-loop's gate is recursive and command
gates can cause direct or indirect re-entrancy.	 When the executing on a
client's thread runCommand 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 arg0 Parameter for action of command gate, defaults to 0.
    @param arg1 Parameter for action of command gate, defaults to 0.
    @param arg2 Parameter for action of command gate, defaults to 0.
    @param arg3 Parameter for action of command gate, defaults to 0.
    @result kIOReturnSuccess if successful. kIOReturnNotPermitted if this
event source is currently disabled, kIOReturnNoResources if no action available.
*/
    virtual IOReturn runCommand(void *arg0 = 0, void *arg1 = 0,
				void *arg2 = 0, void *arg3 = 0);

/*! @function runAction
    @abstract Single thread a call to an action with the target 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 command
gates can cause direct or indirect re-entrancy.	 When the executing on a
client's thread runCommand 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 of command gate, defaults to 0.
    @param arg1 Parameter for action of command gate, defaults to 0.
    @param arg2 Parameter for action of command gate, defaults to 0.
    @param arg3 Parameter for action of command gate, defaults to 0.
    @result kIOReturnSuccess if successful. kIOReturnBadArgument if action is not defined, kIOReturnNoResources if no action available.
*/
    virtual IOReturn runAction(Action action,
			       void *arg0 = 0, void *arg1 = 0,
			       void *arg2 = 0, void *arg3 = 0);
};

#endif /* !_IOKIT_IOCOMMANDGATE_H */