# Set and Get

Sonic Pi has a global memory store called Time State. The two main things you do with it are to `set` information and `get` information. Let’s dive deeper…

## Set

To store information into the Time State we need two things:

1. the information we want to store,
2. a unique name (key) for the information.

For example, we might want to store the number `3000` with the key `:intensity`. This is possible using the `set` function:

    set :intensity, 3000

We can use any name for our key. If information has already been stored with that key, our new `set` will override it:

    set :intensity, 1000
    set :intensity, 3000

In the above example, as we stored both numbers under the same key, the last call to `set` ‘wins’, so the number associated with `:intensity` will be `3000` as the first call to `set` is effectively overridden.

## Get

To fetch information from the Time State we just need the key we used to `set` it, which in our case is `:intensity`. We then just need to call `get[:intensity]` which we can see by printing out the result to the log:

    print get[:intensity] #=> prints 3000

Notice that calls to `get` can return information that was `set` in a previous run. Once a piece of information has been `set` it is available until either the information is overridden (just like we clobbered the `:intensity` value of `1000` to `3000` above) or Sonic Pi is closed.

## スレッド

The main benefit of the Time State system is that it can be safely used across threads or live loops. For example, you could have one live loop setting information and another one getting it:

    rrand

The nice thing about using `get` and `set` across threads like this is that it will always produce the same result every time you hit run. Go on, try it. See if you get the following in your log:

    {run: 0, time: 0.0}
     └─ 125.72265625
    {run: 0, time: 0.5}
     └─ 125.72265625
    {run: 0, time: 1.0}
     └─ 76.26220703125
    {run: 0, time: 1.5}
     └─ 76.26220703125
    {run: 0, time: 2.0}
     └─ 114.93408203125
    {run: 0, time: 2.5}
     └─ 114.93408203125
    {run: 0, time: 3.0}
     └─ 75.6048583984375
    {run: 0, time: 3.5}
     └─ 75.6048583984375

Try running it a few times - see, it’s the same every time. This is what we call deterministic behaviour and it’s really very important when we want to share our music as code and know that the person playing the code is hearing exactly what we wanted them to hear (just like playing an MP3 or internet stream sounds the same for all listeners).

## A Simple Deterministic State System

rand

    ## An Example of Non-Deterministic Behaviour
    ## (due to race conditions caused by multiple
    ## live loops manipulating the same variable
    ## at the same time).
    ##
    ## If you run this code you'll notice
    ## that the list that's printed is
    ## not always sorted!
    a = (ring 6, 5, 4, 3, 2, 1)
    live_loop :shuffled do
      a = a.shuffle
      sleep 0.5
    end
    live_loop :sorted do
      a = a.sort
      sleep 0.5
      puts "sorted: ", a
    end

Let’s take a look at how this might look using `get` and `set`:

    ## An Example of Deterministic Behaviour
    ## (despite concurrent access of shared state)
    ## using Sonic Pi's new Time State system.
    ##
    ## When this code is executed, the list that's
    ## printed is always sorted!
    set :a, (ring 6, 5, 4, 3, 2, 1)
    live_loop :shuffled do
      set :a, get[:a].shuffle
      sleep 0.5
    end
    live_loop :sorted do
      set :a, get[:a].sort
      sleep 0.5
      puts "sorted: ", get[:a]
    end

Notice how this code is pretty much identical to the version using a variable before it. However when you run the code, it behaves as you would expect with any typical Sonic Pi code - it does the same thing every time in this case thanks to the Time State system.

Therefore, when sharing information across live loops and threads, use `get` and `set` instead of variables for deterministic, reproducible behaviour.