- A thread is a thread of execution
- Multiple threads in the same program concurrently
- Threads share the same memory address space
- Changes made by one thread may be read by others
- Threads vs. Processes
- Threads are lightweight; processes are heavyweight
- Threads share address space; processors don't
- Threads require synchronization; processores don't
- It's unsafe to kill threads; same to kill processes
- Reasons to use threads
- Performance needed for blocking activities
- Performance on multi-core processors
- Natural concurrency in the real-world
- Existing multi-threaded, managed run-time environment.
Runnable greeter = new Runnable() {public void run() {doSomething}} // the same as Runnable greeter () -> doSomething()
new Thread(greeter).start()- Synchronization
- No shared mutable state
- Don't mutate
- Don't share
- Synchronize properly
- Challenge
- Safety failure: Not enough synchronization
- Liveness failure: Too much synchronization
- No shared mutable state