Java multi-thread learning notes and multi-thread learning notes

Java multi-thread learning notes and multi-thread learning notes

Concept:

1. Differences between concurrency and Parallelism:

Concurrency: one processor processes multiple tasks simultaneously

Parallel (Parallelism): Multiple Processors "simultaneously" process multiple tasks

 

2. Advantages and Disadvantages of multithreading:

Advantages of multithreading:

Tasks can be processed in parallel to reduce the waiting time of a single task.

The system overhead of a thread is smaller than that of a process or sub-process.

It is easier to share resources between threads.

CPU resources can be fully utilized in multi-core scenarios

Disadvantages of multithreading: Access conflict lock contention-deadlock-lock granularity context switching overhead synchronization/memory copy overhead

 

 

JVM part:

 

Tinking In Java:

1. Concurrency is deterministic but not deterministic.

2. If no task is blocked, it makes no sense to use concurrency on a single processor machine.

3. Some programming languages are designed to isolate concurrent tasks from each other. These languages are generally called function-based languages-erlang.

4. syntax sugar: while (countDown --> 0), private final int id = taskCount ++; Use the plus (+) and minus (--) pairs to add and subtract counters, which is convenient and clear.

5. Various executors ):

CachedThreadPool: generally preferred. It is created on the same number of threads.

FixedThreadPool: specifies the number of threads in advance.

SingleThreadExecutor is like a FixedThreadPool with a thread count of 1 (it provides long-term survival and concurrency assurance, and is suitable for some specific tasks ). SingleThreadExecutor serializes all tasks submitted to it.

6. If you want to return a value when the task is completed, use callable instead of runnable interface.

7.