Order

What "Order" Actually Means

Consider command flow A --> B.

Even if commands are executed in order, you can still get wrong results.

Because order alone doesn't guarantee:

That A has finished
That A's memory writes are visible
That A's results are usable by B

You can expect three different categories:

Execution order
Completion
Memory visibility

and GL only guarantees the first one by default.

Quick mental model check:

Code snippet:
java
```
GL.uploadData();
GL.draw(); // based on the data we just uploaded
```
1
2
Is it safe?
Yes. This is a CPU-to-GPU memory copy which is implicitly protected by GL. The data is visible to the draw command.

Note:
To illustrate, CPU data is gathered at the return stage of GL.uploadData() but GPU side data copy completes later. The draw command is guaranteed to run when everything is ready; the draw action, however, doesn't wait for the data to upload, because a draw call isn't merely about the data and isn't even an action completed in one shot.

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