What causes spurious wakeups?
It’s called spurious because the thread has seemingly been awakened for no reason. But spurious wakeups don’t happen for no reason: they usually happen because, in between the time when the condition variable was signaled and when the waiting thread finally ran, another thread ran and changed the condition.
How do I stop spurious wakeups?
To avoid spurious wakeups, you should ensure that the predicate did not hold before the wakeup and does hold afterwards. You can use preconditions and monitor invariants to guarantee this, but if you do, be sure to document them clearly!
How often do spurious wakeups happen?
In busy periods, up to 20% of the wakeups are spurious (ie when it wakes there is nothing in the queue).
What is the difference between unique_lock and Lock_guard?
A lock_guard always holds a lock from its construction to its destruction. A unique_lock can be created without immediately locking, can unlock at any point in its existence, and can transfer ownership of the lock from one instance to another.
What is wait in thread?
Simply put, wait() is an instance method that’s used for thread synchronization. It can be called on any object, as it’s defined right on java. lang. Object, but it can only be called from a synchronized block. It releases the lock on the object so that another thread can jump in and acquire a lock.
What do you need to know about spurious wakeup?
Spurious wakeup describes a complication in the use of condition variables as provided by certain multithreading APIs such as POSIX Threads and the Windows API . Even after a condition variable appears to have been signaled from a waiting thread’s point of view, the condition that was awaited may still be false.
Why do I get spurious wakeups in my multithreading system?
“a thread might be awoken from its waiting state even though no thread signaled the condition variable”. “Spurious wakeups may sound strange, but on some multiprocessor systems, making condition wakeup completely predictable might substantially slow all condition variable operations.” Sounds like a bug that just isn’t worth fixing, is that right?
When does a spurious wake up occur in Solaris?
In the Solaris implementation of condition variables, a spurious wakeup may occur without the condition being signaled if the process is signaled; the wait system call aborts and returns EINTR. The Linux pthread implementation of condition variables guarantees it will not do that.
What is the difference between spurious and forced oversleep?
Spurious wakeup: waiting thread is scheduled before condition has been established. Forced oversleep: waiting thread is scheduled after condition has been falsified again. Since the later might happen, some went as far as introducing spurious wakeup in the contract: to enforce good practices by requiring predicate loops.