AI_IPC::DbusWatches Class Reference

Utility object to handle installing / removing dbus watches from the poll loop. More...

#include <DbusWatches.h>

Collaboration diagram for AI_IPC::DbusWatches:

Classes
struct	_WatchEntry

Public Member Functions
	DbusWatches (DBusConnection *conn)
int	fd () const
	Returns the epoll fd that the dispatcher should poll on.
void	processEvent (unsigned int pollEvents)
	Called when something has happened on the epoll event loop. More...

Private Types
typedef struct AI_IPC::DbusWatches::_WatchEntry	WatchEntry

Private Member Functions
dbus_bool_t	addWatch (DBusWatch *watch)
	Callback from dbus to add a new watch to poll on. More...
void	toggleWatch (DBusWatch *watch)
	Toggles the watch flags on the given watch. More...
void	removeWatch (DBusWatch *watch)
	Removes the watch from the epoll loop and our local array. More...
uint64_t	createWatch (DBusWatch *watch, int duppedFd)
	Tries to find a slot to put the watch into. More...
void	deleteWatch (uint64_t tag)
	Removes a watch from our internal array. More...

Static Private Member Functions
static dbus_bool_t	addWatchCb (DBusWatch *watch, void *userData)
static void	toggleWatchCb (DBusWatch *watch, void *userData)
static void	removeWatchCb (DBusWatch *watch, void *userData)

Private Attributes
DBusConnection *const	mDbusConnection
int	mEpollFd
uint64_t	mTagCounter
WatchEntry	mWatches [mMaxWatches]
struct epoll_event	mEpollEvents [mMaxWatches]
const std::thread::id	mExpectedThreadId

Static Private Attributes
static const unsigned	mMaxWatches = 128

Detailed Description

Utility object to handle installing / removing dbus watches from the poll loop.

Warning

This class is not thread safe, it is designed to only be called from one thread which is the same thread the libdbus callbacks will be called from. On debug builds an error will be reported if called from an invalid thread.

Internally it creates an epoll object that has watches (which are just fds) added to / removed from it. The epoll fd is returned by this object, and the dispatch poll loop will poll on this. So in effect this is a second level of poll file descriptors.

This code automatically installs the dbus callbacks on the connection at construction time, and removes the callbacks at destruction.

When watches are added we dup the file descriptors, and add the dupped fd to epoll. The reason for this is that libdbus tends to have more than one watch associated with a single fd and you can't add the same fd more once to an epoll event loop. By dup'ing the file descriptors it means we can have one epoll event entry per dbus watch.

Member Function Documentation

addWatch()

dbus_bool_t DbusWatches::addWatch ( DBusWatch *  watch )

private

Callback from dbus to add a new watch to poll on.

libdus should call this function from the dispatch loop thread. We are responsible for adding the watch file descriptor to the poll loop with the given watch flags. When we're woken by one of these we then need to call the watch's dispatch function (called in processEvent()).

Parameters

[in]

watch

The dbus watch object to add

Returns

TRUE on success and FALSE on failure.

createWatch()

uint64_t DbusWatches::createWatch ( DBusWatch *  watch, int  duppedFd  )

private

Tries to find a slot to put the watch into.

We store the watches in an internal array, each watch has a unique 64-bit tag number, this tag is added to the epoll event so we can quickly find the watch that triggered the event.

The lower bits of the tag number are the index into the internal array.

Parameters

[in]	watch	The dbus watch object
[in]	duppedFd	The dup'ed file descriptor for the watch

Returns

on success a non-zero tag number, on failure 0.

deleteWatch()

void DbusWatches::deleteWatch ( uint64_t  tag )

private

Removes a watch from our internal array.

Parameters

[in]

tag

The tag number of the watch to remove

processEvent()

void DbusWatches::processEvent

(

unsigned int

pollEvents

)

Called when something has happened on the epoll event loop.

The main disaptcher loop polls on the fd we supply, when anything changes then this method is called.

Parameters

[in]

pollEvents

Bitmask of the poll events that woke the main loop.

removeWatch()

void DbusWatches::removeWatch ( DBusWatch *  watch )

private

Removes the watch from the epoll loop and our local array.

libdus should call this function from the dispatch loop thread. We check whether the watch has been added, and if so we remove it from epoll.

Parameters

[in]

watch

The dbus watch object to remove

toggleWatch()

void DbusWatches::toggleWatch ( DBusWatch *  watch )

private

Toggles the watch flags on the given watch.

libdus should call this function from the dispatch loop thread. This just changes the epoll event flags to match the new dbus watch flags for the given watch.

Parameters

[in]

watch

The dbus watch object to add

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The documentation for this class was generated from the following files:

• AppInfrastructure/IpcService/source/libdbus/DbusWatches.h
• AppInfrastructure/IpcService/source/libdbus/DbusWatches.cpp