Nxt-python-threads

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Thread Basics

• Computing device - CPU, RAM, persistant store (two ARM CPUs, etc. in the NXT)
• Stored program; Fetch, decode, execute
• Execution context - instructions, data, program counter, stack
  • Processes have all 4 (instructions, data, program counter, stack)
  • Threads have PC and stack with shared ins and data
• Workshop analogy
• Concurrency and locking
• Issues and how they can be addressed
  • Race conditions
  • Deadlock

Basics of threads in Python

Modules

• thread - low level thread library
• threading - higher level library built on thread (addressed on this page)

Thread Objects

When creating a thread, you will must always define a class function called run(). This is the code that will be executed by the thread. When the run() function exits, the thread is no longer alive.

import threading

class hello_world_thread( threading.Thread ):
  def run( self ):
    print "Hello World!"

Starting the above thread is done by calling the start() function. This will execute the run() function you've defined.

>>> hw = hello_world_thread() # initialize
>>> hw.start()                # run
Hello World!

If you want to pass arguments to the thread at initialization, define the constructor function: __init__().

class hello_world_thread( threading.Thread ):
  def __init__( self, message="Hello World" ): # default value for message
    threading.Thread.__init__( self ) # init the thread
    self.message = message

  def run( self ):
    print self.message

>>> hello_world_thread().start() # initialize and run
Hello World!

>>> hello_world_thread('Hola Mundo!").start() # init and run with argument
Hola Mundo! 

Lock Objects Condition Objects Semaphore Objects Event Objects Timer Objects