What is InheritableThreadLocal?

InheritableThreadLocal class extends ThreadLocal to provide inheritance of values from parent thread to child thread: when a child thread is created, the child receives initial values for all inheritable thread-local variables for which the parent has values.

How does ThreadLocal cause memory leak?

Memory leaks can occur when holding threads are re-used which is the case on application servers using pool of threads. To avoid such problems, it is recommended to always clean up ThreadLocal variables using the remove() method to remove the current thread’s value for the ThreadLocal variable.

Are thread locals bad?

I don’t think there is anything wrong with threadlocals – yes, it is a global variable, but besides that it’s a normal tool. We use it just for this purpose (storing subdomain model in the context global to the current request from middleware) and it works perfectly.

What is ThreadLocal class used for?

The ThreadLocal class is used to create thread local variables which can only be read and written by the same thread. For example, if two threads are accessing code having reference to same threadLocal variable then each thread will not see any modification to threadLocal variable done by other thread.

How fast is ThreadLocal?

Summary. A thread local is around 10-20x that of the heap read.

How do I clear a local thread?

There is no way to cleanup ThreadLocal values except from within the thread that put them in there in the first place (or when the thread is garbage collected – not the case with worker threads).

How does the inheritablethreadlocal class work in Java?

InheritableThreadLocal. The InheritableThreadLocal class is a subclass of ThreadLocal . Instead of each thread having its own value inside a ThreadLocal , the InheritableThreadLocal grants access to values to a thread and all child threads created by that thread.

How to set an initial value on a ThreadLocal object?

Initial ThreadLocal Value. Since values set on a ThreadLocal object only are visible to the thread who set the value, no thread can set an initial value on a ThreadLocal using set() which is visible to all threads. Instead you can specify an initial value for a ThreadLocal object by subclassing ThreadLocal…

Can a thread see the reference to the ThreadLocal variable?

Thus, even if two threads are executing the same code, and the code has a reference to the same ThreadLocal variable, the two threads cannot see each other’s ThreadLocal variables. Thus, the Java ThreadLocal class provides a simple way to make code thread safe that would not otherwise be so.

How often do I need to update my ThreadLocal in Java?

This only needs to be done once per thread. Even if different threads execute the same code which accesses a ThreadLococal, each thread will see only its own ThreadLocal instance. Even if two different threads set different values on the same ThreadLocal object, they cannot see each other’s values.