SH-4371 Reduce 22mS inter-connection latency.

This really extended into the client-side request throttling.
Moved this from llmeshrepository (which doesn't really want
to do connection management) into llcorehttp.  It's now a
class option with configurable rate.  This still isn't the
right thing to do as it creates coupling between viewer
and services.  When we get to pipelining, this notion becomes
invalid.

6 files changed, 103 insertions, 7 deletions

diff --git a/indra/llcorehttp/_httpinternal.h b/indra/llcorehttp/_httpinternal.h
index 80f4f34942..effc6a42c5 100755
--- a/indra/llcorehttp/_httpinternal.h
+++ b/indra/llcorehttp/_httpinternal.h
@@ -143,6 +143,7 @@ const int HTTP_CONNECTION_LIMIT_MAX = 256;
 // Miscellaneous defaults
 const long HTTP_PIPELINING_DEFAULT = 0L;
 const bool HTTP_USE_RETRY_AFTER_DEFAULT = true;
+const long HTTP_THROTTLE_RATE_DEFAULT = 0L;
 
 // Tuning parameters
 
diff --git a/indra/llcorehttp/_httppolicy.cpp b/indra/llcorehttp/_httppolicy.cpp
index 32a9ba282a..808eebc6cc 100755
--- a/indra/llcorehttp/_httppolicy.cpp
+++ b/indra/llcorehttp/_httppolicy.cpp
@@ -49,12 +49,18 @@ struct HttpPolicy::ClassState
 {
 public:
 	ClassState()
+		: mThrottleEnd(0),
+		  mThrottleLeft(0L),
+		  mRequestCount(0L)
 		{}
 	
 	HttpReadyQueue		mReadyQueue;
 	HttpRetryQueue		mRetryQueue;
 
 	HttpPolicyClass		mOptions;
+	HttpTime			mThrottleEnd;
+	long				mThrottleLeft;
+	long				mRequestCount;
 };
 
 
@@ -190,6 +196,13 @@ void HttpPolicy::retryOp(HttpOpRequest * op)
 // the worker thread may sleep hard otherwise will ask for
 // normal polling frequency.
 //
+// Implements a client-side request rate throttle as well.
+// This is intended to mimic and predict throttling behavior
+// of grid services but that is difficult to do with different
+// time bases.  This also represents a rigid coupling between
+// viewer and server that makes it hard to change parameters
+// and I hope we can make this go away with pipelining.
+//
 HttpService::ELoopSpeed HttpPolicy::processReadyQueue()
 {
 	const HttpTime now(totalTime());
@@ -199,12 +212,22 @@ HttpService::ELoopSpeed HttpPolicy::processReadyQueue()
 	for (int policy_class(0); policy_class < mClasses.size(); ++policy_class)
 	{
 		ClassState & state(*mClasses[policy_class]);
+		const bool throttle_enabled(state.mOptions.mThrottleRate > 0L);
+		const bool throttle_current(throttle_enabled && now < state.mThrottleEnd);
+
+		if (throttle_current && state.mThrottleLeft <= 0)
+		{
+			// Throttled condition, don't serve this class but don't sleep hard.
+			result = HttpService::NORMAL;
+			continue;
+		}
+
 		int active(transport.getActiveCountInClass(policy_class));
 		int needed(state.mOptions.mConnectionLimit - active);		// Expect negatives here
 
 		HttpRetryQueue & retryq(state.mRetryQueue);
 		HttpReadyQueue & readyq(state.mReadyQueue);
-		
+
 		if (needed > 0)
 		{
 			// First see if we have any retries...
@@ -218,10 +241,27 @@ HttpService::ELoopSpeed HttpPolicy::processReadyQueue()
 				
 				op->stageFromReady(mService);
 				op->release();
-					
+
+				++state.mRequestCount;
 				--needed;
+				if (throttle_enabled)
+				{
+					if (now >= state.mThrottleEnd)
+					{
+						// Throttle expired, move to next window
+						LL_DEBUGS("CoreHttp") << "Throttle expired with " << state.mThrottleLeft
+											  << " requests to go and " << state.mRequestCount
+											  << " requests issued." << LL_ENDL;
+						state.mThrottleLeft = state.mOptions.mThrottleRate;
+						state.mThrottleEnd = now + HttpTime(1000000);
+					}
+					if (--state.mThrottleLeft <= 0)
+					{
+						goto throttle_on;
+					}
+				}
 			}
-		
+			
 			// Now go on to the new requests...
 			while (needed > 0 && ! readyq.empty())
 			{
@@ -231,10 +271,29 @@ HttpService::ELoopSpeed HttpPolicy::processReadyQueue()
 				op->stageFromReady(mService);
 				op->release();
 					
+				++state.mRequestCount;
 				--needed;
+				if (throttle_enabled)
+				{
+					if (now >= state.mThrottleEnd)
+					{
+						// Throttle expired, move to next window
+						LL_DEBUGS("CoreHttp") << "Throttle expired with " << state.mThrottleLeft
+											  << " requests to go and " << state.mRequestCount
+											  << " requests issued." << LL_ENDL;
+						state.mThrottleLeft = state.mOptions.mThrottleRate;
+						state.mThrottleEnd = now + HttpTime(1000000);
+					}
+					if (--state.mThrottleLeft <= 0)
+					{
+						goto throttle_on;
+					}
+				}
 			}
 		}
-				
+
+	throttle_on:
+		
 		if (! readyq.empty() || ! retryq.empty())
 		{
 			// If anything is ready, continue looping...
diff --git a/indra/llcorehttp/_httppolicyclass.cpp b/indra/llcorehttp/_httppolicyclass.cpp
index fe4359081a..f34a8e9f1e 100755
--- a/indra/llcorehttp/_httppolicyclass.cpp
+++ b/indra/llcorehttp/_httppolicyclass.cpp
@@ -36,7 +36,8 @@ namespace LLCore
 HttpPolicyClass::HttpPolicyClass()
 	: mConnectionLimit(HTTP_CONNECTION_LIMIT_DEFAULT),
 	  mPerHostConnectionLimit(HTTP_CONNECTION_LIMIT_DEFAULT),
-	  mPipelining(HTTP_PIPELINING_DEFAULT)
+	  mPipelining(HTTP_PIPELINING_DEFAULT),
+	  mThrottleRate(HTTP_THROTTLE_RATE_DEFAULT)
 {}
 
 
@@ -51,6 +52,7 @@ HttpPolicyClass & HttpPolicyClass::operator=(const HttpPolicyClass & other)
 		mConnectionLimit = other.mConnectionLimit;
 		mPerHostConnectionLimit = other.mPerHostConnectionLimit;
 		mPipelining = other.mPipelining;
+		mThrottleRate = other.mThrottleRate;
 	}
 	return *this;
 }
@@ -59,7 +61,8 @@ HttpPolicyClass & HttpPolicyClass::operator=(const HttpPolicyClass & other)
 HttpPolicyClass::HttpPolicyClass(const HttpPolicyClass & other)
 	: mConnectionLimit(other.mConnectionLimit),
 	  mPerHostConnectionLimit(other.mPerHostConnectionLimit),
-	  mPipelining(other.mPipelining)
+	  mPipelining(other.mPipelining),
+	  mThrottleRate(other.mThrottleRate)
 {}
 
 
@@ -79,6 +82,10 @@ HttpStatus HttpPolicyClass::set(HttpRequest::EPolicyOption opt, long value)
 		mPipelining = llclamp(value, 0L, 1L);
 		break;
 
+	case HttpRequest::PO_THROTTLE_RATE:
+		mThrottleRate = llclamp(value, 0L, 1000000L);
+		break;
+
 	default:
 		return HttpStatus(HttpStatus::LLCORE, HE_INVALID_ARG);
 	}
@@ -103,6 +110,10 @@ HttpStatus HttpPolicyClass::get(HttpRequest::EPolicyOption opt, long * value) co
 		*value = mPipelining;
 		break;
 
+	case HttpRequest::PO_THROTTLE_RATE:
+		*value = mThrottleRate;
+		break;
+
 	default:
 		return HttpStatus(HttpStatus::LLCORE, HE_INVALID_ARG);
 	}
diff --git a/indra/llcorehttp/_httppolicyclass.h b/indra/llcorehttp/_httppolicyclass.h
index 69fb459d22..38f1194ded 100755
--- a/indra/llcorehttp/_httppolicyclass.h
+++ b/indra/llcorehttp/_httppolicyclass.h
@@ -63,6 +63,7 @@ public:
 	long						mConnectionLimit;
 	long						mPerHostConnectionLimit;
 	long						mPipelining;
+	long						mThrottleRate;
 };  // end class HttpPolicyClass
 
 }  // end namespace LLCore
diff --git a/indra/llcorehttp/_httpservice.cpp b/indra/llcorehttp/_httpservice.cpp
index e21d196a3e..c94249dc2d 100755
--- a/indra/llcorehttp/_httpservice.cpp
+++ b/indra/llcorehttp/_httpservice.cpp
@@ -52,7 +52,8 @@ const HttpService::OptionDescriptor HttpService::sOptionDesc[] =
 	{	false,		true,		true,		false	},		// PO_HTTP_PROXY
 	{	true,		true,		true,		false	},		// PO_LLPROXY
 	{	true,		true,		true,		false	},		// PO_TRACE
-	{	true,		true,		false,		true	}		// PO_ENABLE_PIPELINING
+	{	true,		true,		false,		true	},		// PO_ENABLE_PIPELINING
+	{	true,		true,		false,		true	}		// PO_THROTTLE_RATE
 };
 HttpService * HttpService::sInstance(NULL);
 volatile HttpService::EState HttpService::sState(NOT_INITIALIZED);
diff --git a/indra/llcorehttp/httprequest.h b/indra/llcorehttp/httprequest.h
index 5c54d35a21..651654844a 100755
--- a/indra/llcorehttp/httprequest.h
+++ b/indra/llcorehttp/httprequest.h
@@ -139,23 +139,33 @@ public:
 
 		/// Limits the number of connections used for a single
 		/// literal address/port pair within the class.
+		///
+		/// Per-class only
 		PO_PER_HOST_CONNECTION_LIMIT,
 
 		/// String containing a system-appropriate directory name
 		/// where SSL certs are stored.
+		///
+		/// Global only
 		PO_CA_PATH,
 
 		/// String giving a full path to a file containing SSL certs.
+		///
+		/// Global only
 		PO_CA_FILE,
 
 		/// String of host/port to use as simple HTTP proxy.  This is
 		/// going to change in the future into something more elaborate
 		/// that may support richer schemes.
+		///
+		/// Global only
 		PO_HTTP_PROXY,
 
 		/// Long value that if non-zero enables the use of the
 		/// traditional LLProxy code for http/socks5 support.  If
 		// enabled, has priority over GP_HTTP_PROXY.
+		///
+		/// Global only
 		PO_LLPROXY,
 
 		/// Long value setting the logging trace level for the
@@ -169,12 +179,25 @@ public:
 		/// These values are also used in the trace modes for
 		/// individual requests in HttpOptions.  Also be aware that
 		/// tracing tends to impact performance of the viewer.
+		///
+		/// Global only
 		PO_TRACE,
 
 		/// Suitable requests are allowed to pipeline on their
 		/// connections when they ask for it.
+		///
+		/// Per-class only
 		PO_ENABLE_PIPELINING,
 
+		/// Controls whether client-side throttling should be
+		/// performed on this policy class.  Positive values
+		/// enable throttling and specify the request rate
+		/// (requests per second) that should be targetted.
+		/// A value of zero, the default, specifies no throttling.
+		///
+		/// Per-class only
+		PO_THROTTLE_RATE,
+		
 		PO_LAST  // Always at end
 	};