Engine

Lock order constants. More...

Classes
class	ArchiveChannel
	One archived channel. More...
class	ArchiveChannelStateListener
	Listener for ProcessVariable state info. More...
class	CircularBuffer
	In-Memory buffer for values. More...
class	DisableFilter
	A filter to block samples while disabled. More...
class	Engine
	The base class of the archive engines. More...
class	EngineConfig
	Global engine configuration parameters. More...
class	WritableEngineConfig
	Modifyable global engine configuration parameters. More...
class	EngineConfigListener
	Listener to EngineConfigParser. More...
class	EngineConfigParser
	Reads the config from an XML file that should conform to engineconfig.dtd. More...
class	EngineLocks
	The archive engine. More...
class	EngineServer
	HTTP Server of the Engine. More...
class	GroupInfo
	A Group of channels. More...
class	HTMLPage
	Helper for printing a web page to a socket. More...
struct	PathHandlerList
	Used by HTTPClientConnection to dispatch client requests. More...
class	HTTPServer
	An in-memory web server. More...
class	HTTPClientConnection
	Handler for a HTTPServer's client. More...
class	Named
	Abstract base for a named thingy, does not actually contain the name. More...
class	NamedBase
	A named thingy. More...
class	ProcessVariable
	One process variable. More...
class	ProcessVariableContext
	Context for ProcessVariable instances. More...
class	ProcessVariableFilter
	A filter that a SampleMechanism can place between the ProcessVariable and its ProcessVariableListener implementation. More...
class	ProcessVariableStateListener
	Listener for ProcessVariable state info. More...
class	ProcessVariableValueListener
	Listener for ProcessVariable info. More...
class	ProcessVariableListener
	Listener for ProcessVariable info. More...
class	RepeatFilter
	A filter to combine successive matching samples into a 'repeat count'. More...
class	SampleMechanism
	Sample Mechanism base, has a ProcessVariable and filters its values. More...
class	Scannable
	Interface for something that can be placed on a ScanList. More...
class	ScanList
	A ScanList keeps track of Scannable items. More...
class	TimeFilter
	A filter to remove samples that go back in time or are too futuristic. More...
class	TimeSlotFilter
	Filter that passes one sample per time slot. More...
class	ArchiveChannelEA3
	Original archived channel. More...
class	EngineEA3
	The original archive engine. More...
class	SampleMechanismGetEA3
	Sample Mechanism that performs a periodic 'get'. More...
class	SampleMechanismMonitoredEA3
	Monitored Sample Mechanism. More...
class	SampleMechanismMonitoredGetEA3
	Sample Mechanism that stores periodic samples using a 'monitor'. More...

Detailed Description

Lock order constants.

When locking more than one object from the following list, they have to be taken in this order, for example: First lock the Engine, then an ArchiveChannel, then the ProcessVariableContext.

Classes in Tools like the ThrottledMsgLogger use locks with an order of 100 or higher.

Beyond the reach of this code are locks internal to the CA client library. Possible lock chains:

• Start the engine: Engine, ArchiveChannel, ProcessVariable, ca_...
  Has to lock the Engine to prevent concurrent stop(). This initial scenario created the lock order.
• CA connect or control info callback: CA, PV, channel, group.
  This is basically the reversed lock order! To preserve the lock order, the channel will release the PV lock before locking itself, and unlock itself before locking the group. This does assume that the configuration (group membership etc.) does not change!
  The engine used to maintain a connection count that was updated in here as well, but locking the engine in here results in deadlocks with case 6.
• CA value arrives: CA, PV, channel.
  Maybe enable/disable group, which locks group and other channels. As in 2, the lock order must be preserved.
• HTTP client lists group or channel info:
  Lock Engine, group or channel, maybe channel's PV and ca_state().
  Must lock the engine to prevent concurrent engine changes. DEADLOCK with 2 or 3.
  TODO: Handled by not keeping any locks?
• Stop a channel (including from HTTPClient config update): channel, PV, then ca_*
  Handled as part of 6.
• Stop engine (including ...): engine, channel, PV, ca_
  DEADLOCK with 2 or 3.
  Must lock the engine to prevent concurrent engine changes.
• Change channel or overall config
  Handled after stopping the Engine, reload, then start. No new problems.

The basic PV/CA conflicts need to be handled by PV lock releases whenever calling CA.