Nxt-python-threads - Revision history

Amweeden06 at 13:17, 27 April 2010

2010-04-27T13:17:22Z

← Older revision		Revision as of 13:17, 27 April 2010
Line 152:		Line 152:
	# get candy		# get candy
	candy_bucket.release()		candy_bucket.release()

			=== Generalized kill-switch threading ===
			class thread_wait( threading.Thread ):
			def __init__( self, condition, action ):
			threading.Thread.__init__( self )
			self.condition = condition
			self.action = action

			def run( self ):
			while not self.condition():
			sleep(0.1)
			self.action
			Usage:
			kill_switch_thread = thread_wait( get_kill_switch_function, suicide_function )
			kill_switch_thread.start()

Amweeden06: /* Event Objects (Event) */ There was a small wiki formatting problem

2010-02-25T14:08:05Z

Event Objects (Event): There was a small wiki formatting problem

← Older revision		Revision as of 14:08, 25 February 2010
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	==== Event Objects (Event) ====		==== Event Objects (Event) ====
	Event objects can be used for thread synchronization. When a thread calls <code>wait()</code> for an event that is set, it will continue on immediately. When a thread calls <code>wait()</~~wait~~> for an event that is not set, it will wait until that event is set. More than one thread can be looking for the same event.		Event objects can be used for thread synchronization. When a thread calls <code>wait()</code> for an event that is set, it will continue on immediately. When a thread calls <code>wait()</code> for an event that is not set, it will wait until that event is set. More than one thread can be looking for the same event.

	* set() - set flag to true		* set() - set flag to true

Charliep at 11:36, 25 February 2010

2010-02-25T11:36:56Z

← Older revision		Revision as of 11:36, 25 February 2010
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	** Race conditions		** Race conditions
	** Deadlock		** Deadlock
			** Locks, semaphores, barriers

	=== Basics of threads in Python ===		=== Basics of threads in Python ===
	==== Modules ====		==== Modules ====

Charliep at 11:34, 25 February 2010

2010-02-25T11:34:07Z

← Older revision		Revision as of 11:34, 25 February 2010
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	* Execution context - instructions, data, program counter, stack		* Execution context - instructions, data, program counter, stack
	** Processes have all 4 (instructions, data, program counter, stack)		** Processes have all 4 (instructions, data, program counter, stack)
	** Threads have PC and stack with shared ~~ins~~ and data		** Threads have PC and stack with shared instructions and data
	* Workshop analogy		* Workshop analogy
	* Concurrency and locking		* Concurrency and locking
	* Issues and how they can be addressed
	** Race conditions		** Race conditions
	** Deadlock		** Deadlock

Brad: /* Condition Objects (Condition) */

2010-02-25T06:14:38Z

Condition Objects (Condition)

← Older revision		Revision as of 06:14, 25 February 2010
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	candy_bucket = threading.Lock()		candy_bucket = threading.Lock()
	candy_available = threading.Conditional( candy_bucket )		candy_available = threading.Conditional( candy_bucket )

	# in homeowner's thread		# in homeowner's thread
	candy_bucket.acquire()		candy_bucket.acquire()
Line 145:		Line 145:
	candy_available.notify()		candy_available.notify()
	candy_bucket.release()		candy_bucket.release()

	# in trick-or-treater's thread		# in trick-or-treater's thread
	candy_bucket.acquire()		candy_bucket.acquire()

Brad: /* Modules */

2010-02-25T06:13:33Z

Modules

← Older revision		Revision as of 06:13, 25 February 2010
Line 15:		Line 15:
	==== Modules ====		==== Modules ====
	* <b>[http://docs.python.org/library/thread.html thread]</b> - low level thread library		* <b>[http://docs.python.org/library/thread.html thread]</b> - low level thread library
	* <b>[http://docs.python.org/library/threading.html threading]</b> - higher level library built on thread (addressed on this page~~) ([http://effbot.org/zone/thread-synchronization.htm excellent resource ]~~)		* <b>[http://docs.python.org/library/threading.html threading]</b> - higher level library built on thread (addressed on this page)

	====Thread Objects====		====Thread Objects====

Brad at 06:13, 25 February 2010

2010-02-25T06:13:09Z

← Older revision		Revision as of 06:13, 25 February 2010
Line 151:		Line 151:
	# get candy		# get candy
	candy_bucket.release()		candy_bucket.release()

	~~==== Timer Objects ====~~

Brad: /* Condition Objects (Condition) */

2010-02-25T06:11:04Z

Condition Objects (Condition)

← Older revision		Revision as of 06:11, 25 February 2010
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	Condition objects are essentially a combination of locks and events. You can create a condition using an existing lock or a re-entrant lock will be created if one is not specified.		Condition objects are essentially a combination of locks and events. You can create a condition using an existing lock or a re-entrant lock will be created if one is not specified.

	* acquire()		* acquire() - acquire lock
	* release()		* release() - release lock
	* wait()		* wait() - release the underlying lock and wait for a notification
	* notify()		* notify() - wake up a thread waiting for the condition
	* notifyAll()		* notifyAll() - wake up all threads waiting for the condition

			More than one thread can wait for a condition to be true (indefinitely or with a timeout). If a queue of objects is being processed by multiple threads, a condition can be used by a consumer to acquire access after an element has been added by a producer.

	~~More than one~~ thread ~~can wait for a condition to be true~~ (~~indefinitely~~ or ~~with a timeout~~). ~~If a queue of objects is being processed by multiple threads, a condition can be used by a consumer to acquire access after an element has been added by a producer.~~		# globally defined
			candy_bucket = threading.Lock()
			candy_available = threading.Conditional( candy_bucket )

			# in homeowner's thread
			candy_bucket.acquire()
			# put one black or orange peanut butter candy in bucket
			candy_available.notify()
			candy_bucket.release()

			# in trick-or-treater's thread
			candy_bucket.acquire()
			candy_available.wait()
			# get candy
			candy_bucket.release()

	~~is_alive()~~
	~~self.name~~
	==== Timer Objects ====		==== Timer Objects ====

Brad: /* Event Objects (Event) */

2010-02-25T05:46:51Z

Event Objects (Event)

← Older revision		Revision as of 05:46, 25 February 2010
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	sleep( frustrating_time * 2 )		sleep( frustrating_time * 2 )
	green_light.set()		green_light.set()

	# in driver thread's run function		# in driver thread's run function
	green_light.wait() # block until green_light is set		green_light.wait() # block until green_light is set

Brad: /* Event Objects (Event) */

2010-02-25T05:46:31Z

Event Objects (Event)

← Older revision		Revision as of 05:46, 25 February 2010
Line 101:		Line 101:

	==== Event Objects (Event) ====		==== Event Objects (Event) ====
	Event objects can be used for thread synchronization. ~~There are three class functions: <code>set()</code>, <code>clear()</code> and <code>wait()</code>.~~		Event objects can be used for thread synchronization. When a thread calls <code>wait()</code> for an event that is set, it will continue on immediately. When a thread calls <code>wait()</wait> for an event that is not set, it will wait until that event is set. More than one thread can be looking for the same event.

	When a thread calls <code>wait()</code> for an event that is set, it will continue on immediately. When a thread calls <code>wait()</wait> for an event, it will wait until that event is set. More than one thread can be looking for the same event.

	* set() - set flag to true		* set() - set flag to true