Incoming links: Tree (data structure)
Every tree is a directed acyclic graph.
But not every directed acyclic graph is a tree.
Example of a tree (and therefore also a DAG):Convention in this presentation: arrows implicitly point up, just like in a and so on.
5
|
4 7
| |
3 6
|/
2
|
1git log, i.e.:- 1 is parent of 2
- 2 is parent of 3 and 6
- 3 is parent of 4
Example of a DAG that is not a tree:This is not a tree because there are two ways to reach 7:
7
|\
4 6
| |
3 5
|/
2
|
1- 2, 3, 4, 7
- 2, 5, 6, 7
But we often say "tree" intead of "DAG" in the context of Git because DAG sounds ugly.
Example of a graph that is not a DAG:This one is not acyclic because there is a cycle 2, 3, 4, 5, 2.
6
^
|
3->4
^ |
| v
2<-5
^
|
1God, it's impossible! You just have to convert the entire fucking call stack all the way up to async functions. It could mean refactoring hundreds of functions.
To be fair, there is a logic to this, if you put yourself within the crappiness of the JavaScript threading model. And Python is not that much better with its Global Interpreter Lock.
The problem is that async was introduced relatively late, previously we just had to use infinitely deep callback trees, which was worse:compared to the new infinitely more readable:But now we are in an endless period of transition between both worlds.
myAsync().then(ret => myAsync2(ret).then(ret2 => myAsync3(re3)))ret = await myAsync()
ret2 = await myAsync2(ret)
ret3 = await myAsync3(ret3)It is also worth mentioning that callbacks are still inescapable if you really want to fan out into a non-linear dependency graph, usually with
Promise.all:await Promise.all([
myAsync(1).then(ret => myAsync2(ret)),
myAsync(2).then(ret => myAsync2(ret)),
])Bibliography:
- stackoverflow.com/questions/21819858/how-to-wrap-async-function-calls-into-a-sync-function-in-node-js-or-javascript
- stackoverflow.com/questions/9121902/call-an-asynchronous-javascript-function-synchronously
- stackoverflow.com/questions/47227550/using-await-inside-non-async-function
- stackoverflow.com/questions/43832490/is-it-possible-to-use-await-without-async-in-js
- stackoverflow.com/questions/6921895/synchronous-delay-in-code-execution
And then, after many many hours of this work, you might notice that the new code is way, way way slower than before, because making small functions
async has a large performance impact: madelinemiller.dev/blog/javascript-promise-overhead/. Real world case with a 4x slowdown: github.com/ourbigbook/ourbigbook/tree/async-slow.Anyways, since you Googled here, you might as well learn the standard pattern to convert callbacks functions into async functions using a promise: stackoverflow.com/questions/4708787/get-password-from-input-using-node-js/71868483#71868483
async function Teletubbies meme
. Source. TODO find original source.It is important to note that due to horizontal gene transfer, the early days of life, and still bacteria to this day due to bacterial conjugation, are actually a graph and not a tree, see also: Figure "Graph of life".
Definitely have a look at: coral of life representations.