MySQL pessimistic lock

Pessimistic lock is a kind of thought , seeing the name of a thing one thinks of its function , Is very pessimistic , Be conservative about data being modified by other transactions , It will be realized through the lock mechanism of the database itself , So as to ensure the exclusivity of data operation .
Pessimistic lock always assumes the worst , Every time I go to get the data, I think others will modify it , So every time I get the data, I lock it , So that if people want to take this data, they will Blocking Until it gets the lock （ Shared resources are used by only one thread at a time , Other threads are blocking , Transfer resources to other threads after use ）. For example, line locks. , Table lock, etc. , Read the lock , Write locks, etc. , It's all locked before the operation , When other threads want to access data , All need to block pending .Java in synchronized and ReentrantLock Waiting for exclusive lock is the realization of pessimistic lock thought .