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Rewrote in simple language. Deleted an irrelevant example.

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Ron Hale-Evans 2016-06-24 10:25:47 -07:00
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docs/reference/control/in-background.md
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@ -1,15 +1,25 @@
# In Background
# Run In Background
Run code in the background as a separate process or thread; for more information on this advanced construct, see [the micro:bit - a reactive system](/device/reactive).
Run part of a program while the rest of it is doing something else.
```sig
control.inBackground(() => {
})
```
### ~hint
For more information, read
[The micro:bit - a reactive system](/device/reactive).
It is pretty advanced!
### ~
### Example
The example below shows how a background process can be used to display the current value of the global variable `num`, while code (like the `on button pressed` handler) can change the value of the variable.
This program shows how running in the background can say what is
stored in a variable like `num`, while another part (``on button pressed``)
changes what is stored there.
```blocks
let num = 0
@ -24,7 +34,8 @@ input.onButtonPressed(Button.A, () => {
})
```
The code below using the `forever` loop is equivalent to the code above
This program does the same thing, but in a more usual way,
with a ``forever`` loop.
```blocks
let num = 0
@ -36,20 +47,8 @@ input.onButtonPressed(Button.A, () => {
})
```
### Contention for the LED display
If you have multiple processes that each show something on the LED screen, you may get unexpected results. Try, for example:
```blocks
basic.forever(() => {
basic.showNumber(6789, 150)
})
input.onButtonPressed(Button.A, () => {
basic.showNumber(2, 150)
})
```
### See also
[while](/blocks/loops/while), [forever](/reference/basic/forever), [on button pressed](/reference/input/on-button-pressed)
[while](/blocks/loops/while), [forever](/reference/basic/forever),
[on button pressed](/reference/input/on-button-pressed)