Doing several things.
WHAT CONCURRENCY IS
Structuring a program so several tasks can be in progress.
WHAT PARALLELISM IS
Executing several tasks simultaneously, on several cores.
WHY THEY ARE DIFFERENT
Concurrency is about structure. Parallelism is about execution.
WHAT APPROACHES EXIST
Threads, sharing memory Processes, isolated Asynchronous execution on one thread Lightweight tasks managed by the runtime Message passing between isolated units
WHAT SHARED MEMORY CAUSES
Race conditions, where the result depends on timing.
WHAT THOSE ARE LIKE
Intermittent, difficult to reproduce, and among the hardest bugs to diagnose.
WHAT PREVENTS THEM
Locks, used correctly Avoiding shared changing state Message passing
WHAT A GLOBAL INTERPRETER LOCK IS
A mechanism in some runtimes preventing threads executing code simultaneously.
WHAT THAT MEANS
Threads help with waiting, not with computation.
WHAT TO USE FOR COMPUTATION IN THOSE LANGUAGES
Separate processes.
WHAT TO ESTABLISH FOR ANY LANGUAGE
What its model is, and what it protects you from.
