States together with the Component.wait() method provide a powerful way of process interaction.
A state will have a certain value at a given time. In its simplest form a component can then wait for a specific value of a state. Once that value is reached, the component will be resumed.
Definition is simple, like
dooropen=sim.State('dooropen'). The default initial value is False, meaning
the door is closed.
Now we can say
to open the door.
If we want a person to wait for an open door, we could say
If we just want at most one person to enter, we say
We can obtain the current value by just calling the state, like in
print('door is ',('open' if dooropen() else 'closed'))
Alternatively, we can get the current value with the get method
print('door is ',('open' if dooropen.get() else 'closed'))
The value of a state is automatically monitored in the state.value level monitor.
All components waiting for a state are in a salabim queue, called waiters().
States can be used also for non values other than bool type. E.g.
light=sim.State('light', value='red') ... light.state.set('green')
Or define a int/float state
level=sim.State('level', value=0) ... level.set(level()+10)
States have a number of monitors:
- value, where all the values are collected over time
Process interaction with wait()¶
A component can wait for a state to get a certain value. In its most simple form
Once the dooropen state is True, the component will continue.
As with request() it is possible to set a timeout with fail_at or fail_delay
yield self.wait(dooropen, fail_delay=10) if self.failed: print('impatient ...')
In the above example we tested for a state to be True.
There are three ways to test for a value:
It is possible to test for a certain value
yield self.wait((light, 'green'))
Or more states at once
yield self.wait((light, 'green'), night) # honored as soon as light is green OR it's night yield self.wait((light, 'green'), (light, 'yellow')) # honored as soon is light is green OR yellow
It is also possible to wait for all conditions to be satisfied, by adding
yield self.wait((light,'green'), enginerunning, all=True) # honored as soon as light is green AND engine is running
Here, we use a string containing an expression that can evaluate to True or False. This is
done by specifying at least one
$ in the test-string. This
$ will be replaced at run time by
state.value(), where state is the state under test. Here are some examples
yield self.wait((light, '$ in ("green","yellow")')) # if at run time light.value() is 'green', test for eval(state.value() in ("green,"yellow")) ==> True yield self.wait((level, '$ < 30')) # if at run time level.value() is 50, test for eval(state.value() < 30) ==> False
During the evaluation,
self refers to the component under test and
state to the state under test.
self.limit = 30 yield self.wait((level, 'self.limit >= $')) # if at run time level.value() is 10, test for eval(self.limit >= state.get()) ==> True, so honored
This is a more complicated but also more versatile way of specifying the honor-condition. In that case, a function is required to specify the condition. The function needs to accept three arguments:
- x = state.get()
- component component under test
- state under test
yield self.wait((light, lambda x, _, _: x in ('green', 'yellow')) # x is light.get() yield self.wait((level, lambda x, _, _: x >= 30)) # x is level.get()
And, of course, it is possible to define a function
def levelreached(x): value, component, _ = x return value < component.limit ... self.limit = 30 yield self.wait((level, levelreached))
Combination of testing methods¶
It is possible to mix scalar, evaluation and function testing. And it’s also possible to specify all=True in any case.