ThreadSafeVariable

The problem

Imagine you have class like this

class A(object):
    def __init__(self, x):
        self.x = x

a = A(3)
print(a.x)

a.x is a member variable of object a. It is not thread safe. This means that if one thread changes `a.x``, all other threads see the new value. You can avoid this using a thread local object:

import threading

class A(object):    
    def __init__(self, x):
        self.local = threading.local()
        self.local.x

a = A(3)
print(a.local.x)

This works but has two downsides:

• you have changed the syntax
• even if a is accessible from other threads, a.local.x is only defined for the one thread that created the object

The ThreadSafeVariable module helps solve this problem and preserves the original syntax.

The solution

We change the code in the first example by declaring which variables should the thrad safe:

from threadsafevariable import ThreadSafeVariable

class A(object):
    x = ThreadSafeVariable() # we add this line
    def __init__(self, x):
        self.x = x

a = A(3)
print(a.x)

We have preserved the syntax for the first example but a.x is now a thread local variable.

In addition we can do:

iceblock = ThreadSafeVariable.freeze()

This will store a snapshot all ThreadSafeVariable(s) of all objects defined in the current thread. Then for any other thread:

ThreadSafeVariable.restore(iceblock)

will restore all variables of all objects in this thread to the value stores in iceblock.