public:

// Event fired when a new breakpoint update is enqueued. This event is fired

// in the same thread that enqueued the update. The subscriber to this event

// should defer as much work as possible outside of the event callback.

typedef Observable<> OnItemEnqueued;

FormatQueue() { }

~FormatQueue();

// Returns true if FormatQueue has no data, false otherwise.

bool IsEmpty() const;

// Removes everything from the queue. This is typically needed when JVM

// goes down and we want to clean up all the resources.

void RemoveAll();

// Appends the completed breakpoint to the end of the queue. The "breakpoint"

// parameter contains the definition of the breakpoint (without the results).

// The "collector" captures call stack, local variables and objects on

// breakpoint hit and can format the captured data into the protocol message.

// "FormatQueue" takes ownership over "breakpoint" and "collector". "Enqueue"

// honors the "kMaxPendingResults" limit and discards the breakpoint if

// threshold is reached.

// "jni" is used to provide JNI context to "OnItemEnqueued" event.

void Enqueue(

std::unique_ptr<BreakpointModel> breakpoint,

std::unique_ptr<CaptureDataCollector> collector);

// If the queue is empty, returns nullptr. Otherwise pops the first entry in

// the queue, formats it (i.e. combines breakpoint definition with breakpoint

// results and captures immutable Java objects) and returns it to the caller.

std::unique_ptr<BreakpointModel> FormatAndPop();

// Subscribes to receive OnItemEnqueued notifications.

OnItemEnqueued::Cookie SubscribeOnItemEnqueuedEvents(

OnItemEnqueued::Callback fn) {

return on_item_enqueued_.Subscribe(fn);

}

// Unsubscribes from OnItemEnqueued notifications.

void UnsubscribeOnItemEnqueuedEvents(OnItemEnqueued::Cookie cookie) {

on_item_enqueued_.Unsubscribe(std::move(cookie));

}

private:

// Single item in a queue.

struct Item {

// Breakpoint definition typically without results. "breakpoint" may

// include hit results if collector is nullptr.

std::unique_ptr<BreakpointModel> breakpoint;

// Capture of call stack, local variables and objects on breakpoint hit.

std::unique_ptr<CaptureDataCollector> collector;

};

// Locks access to the queue.

mutable absl::Mutex mu_;

// Breakpoint hit results that wait to be reported to the hub. The list is

// used as queue. It is important to use linked list here, so that the pointer

// to "Item" returned by "Top" remains valid while new elements are pushed

// into the queue.

std::list<Item> queue_;

// Allows other objects to receive synchronous notifications each time

// a new breakpoint update is enqueued.

OnItemEnqueued on_item_enqueued_;

DISALLOW_COPY_AND_ASSIGN(FormatQueue);