where parallel paths converge
Concurrency is the art of doing many things at once without losing track of any of them. Like streams converging in a marble quarry, each thread follows its own path through the stone, yet all contribute to the pattern that emerges.
In the garden of computation, every stone is a process waiting to be placed. The arrangement matters less than the patience of placement.
A deadlock is a meditation interrupted. Two processes, each waiting for the other, locked in perfect stillness. Even failure has its beauty.
The quarry reveals what was always there. Marble does not become beautiful through cutting; the veins existed before the chisel. So too with concurrent systems: the parallelism was always present in the problem. We merely expose it.
Parallel lines never meet, yet they define the same direction. Concurrent threads may never share state, yet they compose the same computation.
To observe a concurrent system is to change it. The act of measurement introduces ordering where none existed. Heisenberg meets Dijkstra in the stone garden.