Make it possible to learn execution isolation strategy for the current command in HystrixConcurrencyStrategy

[dmak]

I suggest to pass HystrixCommandProperties or ExecutionIsolationStrategy to HystrixConcurrencyStrategy#wrapCallable(Callable callable). For example, if ExecutionIsolationStrategy is SEMAPHORE then in my case the given callable can be returned as is, without being wrapped:

HystrixPlugins.getInstance().registerConcurrencyStrategy(new HystrixConcurrencyStrategy() {
    @Override
    public <T> Callable<T> wrapCallable(Callable<T> callable, ExecutionIsolationStrategy strategy) {
        if (strategy == ExecutionIsolationStrategy.SEMAPHORE) {
            return callable;
        }
        return new MyCallable<T>(callable);
    }
});

[mattrjacobs]

Something similar came up in /#1548#1570, in which Hystrix was eagerly calling wrapCallable. After that change, it will now invoke wrapCallable only when:

• putting the Hystrix-wrapped work onto a Hystrix thread (command is thread-isolated)
• executing the fallback on a HystrixTimer thread
• executing a HystrixCollapser-produced command on a HystrixTimer thread

So I don't believe that wrapCallable ever gets invoked on the user-provided work when the command is semaphore-isolated.

[dmak]

I agree. After doublechecking I confirm that wrapCallable is called only from pool thread.