From ec6487f3a70a5067f6d8fc601437160bb4fa753f Mon Sep 17 00:00:00 2001
From: Nat Goodspeed <nat@lindenlab.com>
Date: Thu, 27 Sep 2018 14:57:03 -0400
Subject: [PATCH] DRTVWR-474: Make LLEventMailDrop pass all saved events to
listener.
Previously, LLEventMailDrop would send only the first queued event to a
newly-connected listener. If you wanted to flush all queued events, you'd have
to "pump" the queue by repeatedly disconnecting and reconnecting -- with no
good way to know when you'd caught up.
The new behavior makes LLEventMailDrop resemble a multi-valued future: a
rendezvous between producer and consumer that, once connected, pushes values
rather than requiring them to be pulled (as with a simple queue) -- regardless
of the relative order in which post() and listen() are called.
---
indra/llcommon/llevents.cpp | 23 +++++++++++++++--------
indra/llcommon/llevents.h | 20 +++++++++++++-------
2 files changed, 28 insertions(+), 15 deletions(-)
diff --git a/indra/llcommon/llevents.cpp b/indra/llcommon/llevents.cpp
index dce97b5411d..eedd8c92b5a 100644
--- a/indra/llcommon/llevents.cpp
+++ b/indra/llcommon/llevents.cpp
@@ -545,10 +545,8 @@ bool LLEventStream::post(const LLSD& event)
*****************************************************************************/
bool LLEventMailDrop::post(const LLSD& event)
{
- bool posted = false;
-
- if (!mSignal->empty())
- posted = LLEventStream::post(event);
+ // forward the call to our base class
+ bool posted = LLEventStream::post(event);
if (!posted)
{ // if the event was not handled we will save it for later so that it can
@@ -564,16 +562,25 @@ LLBoundListener LLEventMailDrop::listen_impl(const std::string& name,
const NameList& after,
const NameList& before)
{
- if (!mEventHistory.empty())
+ // Before actually connecting this listener for subsequent post() calls,
+ // first feed each of the saved events, in order, to the new listener.
+ // Remove any that this listener consumes -- Effective STL, Item 9.
+ for (auto hi(mEventHistory.begin()), hend(mEventHistory.end()); hi != hend; )
{
- if (listener(mEventHistory.front()))
+ if (listener(*hi))
{
- mEventHistory.pop_front();
+ // new listener consumed this event, erase it
+ hi = mEventHistory.erase(hi);
+ }
+ else
+ {
+ // listener did not consume this event, just move along
+ ++hi;
}
}
+ // let base class perform the actual connection
return LLEventStream::listen_impl(name, listener, after, before);
-
}
diff --git a/indra/llcommon/llevents.h b/indra/llcommon/llevents.h
index 1d51c660ed0..5d60c638101 100644
--- a/indra/llcommon/llevents.h
+++ b/indra/llcommon/llevents.h
@@ -650,15 +650,21 @@ class LL_COMMON_API LLEventStream: public LLEventPump
* LLEventMailDrop
*****************************************************************************/
/**
- * LLEventMailDrop is a specialization of LLEventStream. Events are posted normally,
- * however if no listeners return that they have handled the event it is placed in
- * a queue. Subsequent attaching listeners will receive stored events from the queue
- * until a listener indicates that the event has been handled. In order to receive
- * multiple events from a mail drop the listener must disconnect and reconnect.
+ * LLEventMailDrop is a specialization of LLEventStream. Events are posted
+ * normally, however if no listener returns that it has handled the event
+ * (returns true), it is placed in a queue. Subsequent attaching listeners
+ * will receive stored events from the queue until some listener indicates
+ * that the event has been handled.
+ *
+ * LLEventMailDrop completely decouples the timing of post() calls from
+ * listen() calls: every event posted to an LLEventMailDrop is eventually seen
+ * by all listeners, until some listener consumes it. The caveat is that each
+ * event *must* eventually reach a listener that will consume it, else the
+ * queue will grow to arbitrary length.
*
* @NOTE: When using an LLEventMailDrop (or LLEventQueue) with a LLEventTimeout or
- * LLEventFilter attaching the filter downstream using Timeout's constructor will
- * cause the MailDrop to discharge any of it's stored events. The timeout should
+ * LLEventFilter attaching the filter downstream, using Timeout's constructor will
+ * cause the MailDrop to discharge any of its stored events. The timeout should
* instead be connected upstream using its listen() method.
* See llcoro::suspendUntilEventOnWithTimeout() for an example.
*/
--
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