About Python threading Lock Object

Question

I am reading Python Threading Lock API.
Link here.

I am wondering what does the statement below mean.

"When the state is locked, acquire() blocks until a call to release() in another thread changes it to unlocked, then the acquire() call resets it to locked and returns."

I have read this statement 100 times. Still can't get it.

Why another thread to unlock? What does the statement after 'then' mean?

Is there any good explanation for this?

Answer 1

The overall meaning is that when a lock is acquired from a thread, other threads that call acquire waits untill the lock is released and lock it again:

When the state is locked,

Thread A acquire() the lock

acquire() blocks

Thread B try to acquire() the lock, but it is locked, so acquire() block current thread

until a call to release() in another thread changes it to unlocked

until the lock is released somewhere else (ie, it waits untill thread A release() the lock)

then the acquire() call resets it to locked and returns.

the acquire() of thread B locks the lock again