Can anyone please tell me the purpose of ThreadLocal in DomainEventPublisher? about iddd_samples HOT 10 OPEN

The DomainEventPublisher (here) is a static and synchronous component where events are published synchronously in the same thread - and subscribed to by the same thread. The ThreadLocal is used to have storage specific to each thread, so different threads can publish at the same time without conflicting.

from iddd_samples.

I totally missed the original comment. The DomainEventPublisher has a static (class-level) interface for obtaining the instance that belongs to the current thread. However, there are also the instance methods publish(), subscribe(), reset(), that operate on the ThreadLocal instance. In any given thread there is likely only one or a few subscribers registered, so it's not a lot of overhead. Also note that at some point when a thread is assigned to an incoming server request, the subscriber list for the thread must be reset using DomainEventPublisher.instance().reset() so that subscriber(s) from the previous request using the same thread will not be left on the subscriber list.

from iddd_samples.

Looking at the implementation of the DomainEventPublisher I struggle to understand why do you have the publishing lock. Because you are running one instance per thread there are no potential concurrency issues. Why would you want to have a lock like that?

Probably I'm missing some fundamental concept. But it seems to me quite redundant based on the fact that you have one instance per Thread (thanks to ThreadLocal).

from iddd_samples.

The DomainEventPublisher must protect itself from the subscribers. For
example, when a subscriber's handle() method has been called back on, the
handle() method could attempt to register another subscriber. Even though
it's all happening on a single thread, that would cause a
ConcurrentModificationException on the collection.

On Thu, Oct 24, 2013 at 3:40 AM, Leonardo Fernandez <
[email protected]> wrote:

Looking at the implementation of the DomainEventPublisher I struggle to
understand why do you have the publishing lock. Because you are running one
instance per thread there are no potential concurrency issues. Why would
you want to have a lock like that?

Probably I'm missing some fundamental concept. But it seems to me quite
redundant based on the fact that you have one instance per Thread (thanks
to ThreadLocal).

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/6#issuecomment-26978779
.

from iddd_samples.

Yeah! I see.

from iddd_samples.

Please see Chapter 8 of my book.

from iddd_samples.

Hum, I am reading this book at now, and thank you very much! It has been translated into Chinese.

from iddd_samples.

what if
thread_A subscribe(payEventSubscriber)
thread_B publish(payEvent)

it can`t work...

from iddd_samples.

from iddd_samples.

i have known that after reading the code.
thanks

from iddd_samples.