docs: add diagrams for decorator, delegation, dependency injection, dirty flag, domain model, double buffer, double-checked locking, double dispatch, and dynamic proxy

double-checked-locking/README.md

@@ -29,6 +29,10 @@ Wikipedia says
 
 > In software engineering, double-checked locking (also known as "double-checked locking optimization") is a software design pattern used to reduce the overhead of acquiring a lock by testing the locking criterion (the "lock hint") before acquiring the lock. Locking occurs only if the locking criterion check indicates that locking is required.
 
+Flowchart
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+![Double-Checked Locking flowchart](./etc/double-checked-locking-flowchart.png)
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 ## Programmatic Example of Double-Checked Locking Pattern in Java
 
 The Double-Checked Locking pattern is used in the `HolderThreadSafe` class to ensure that the `Heavy` object is only created once, even when accessed from multiple threads.  Here's how it works: