About multithreading

The relationship between process and operating system ： Process is the basic unit of resource allocation in operating system ;

Threads are the control flow of a single task , yes CPU Minimum unit of scheduling ;
A process can contain multiple threads , Threads depend on the process ;

lock :
① Pessimistic locking ： Pessimistic locks believe that there is a lot of competition between multithreads , The thread grabbing the resource will lock the memory resource , Contention between other threads is not allowed （ For high concurrency , When multithreading ）
② Optimism lock ： Optimistic lock does not think that multiple threads will rob the same memory resource , It is based on the version number , operational （ Suitable for low concurrency , Fewer threads ）
The difference between threads and processes
  1. Each process has its own code and data space ( Process context ), Switching between processes can be costly .
  2. Threads can be thought of as lightweight processes , Threads belonging to the same process share code and data space , Each thread has a separate running stack and program counter (PC), Low cost of thread switching .
  3. The fundamental difference between threads and processes is ： A process is a unit of resource allocation , A thread is the unit of scheduling and execution .
  4. Multi process : Multiple tasks can be run simultaneously in the operating system ( Program ).
  5. Multithreading : Multiple sequential flows execute simultaneously in the same application .
  6. Threads are part of the process , So threads are sometimes called lightweight processes .
  7. A process without threads can be regarded as a single thread , If there are multiple threads in a process , The execution of a process is not a line ( Threads ) Of , It's multiple lines ( Threads ) Jointly completed .
  8. When the system is running, it will allocate different memory areas for each process , But memory is not allocated to threads ( The resource used by a thread is the resource of the process to which it belongs ), Thread groups can only share resources . That is to say , except CPU outside ( The thread needs to occupy when it is running CPU resources ), The allocation of software and hardware resources in a computer has nothing to do with threads , A thread can only share the resources of the process to which it belongs .