From e79a88c8ccfadcd260892000d4dec2ae921b26de Mon Sep 17 00:00:00 2001
From: Monty Brandenberg <monty@lindenlab.com>
Date: Tue, 12 Aug 2014 18:21:26 -0400
Subject: Better support for dynamic option changes in llcorehttp.  Libcurl has
 some problems disabling pipelining on a multi handle with outstanding
 requests so build a more conservative system that allows requests to drain
 before setting curl multi options.  Would rather not have this but it is
 significantly safer.  "HttpPipelining" debug setting is now fully dynamic. 
 Connection limits can also be made dynamic in the near future.  Upped the
 default connection count back to 8 for now but will revisit this in the
 tuning phase.  It might be time to combine mesh and textures into a single
 asset class.  For normal server operations that would be a clear path, but
 for server under load, the current scheme may be better.  Minor cleanup in
 logging to elminate some redundant strings.  Might add some more tracing to
 the stall logic 'just in case'.

---
 indra/newview/lltexturefetch.cpp | 55 +++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 21 deletions(-)

(limited to 'indra/newview/lltexturefetch.cpp')

diff --git a/indra/newview/lltexturefetch.cpp b/indra/newview/lltexturefetch.cpp
index 4008a6948d..097a7b374f 100755
--- a/indra/newview/lltexturefetch.cpp
+++ b/indra/newview/lltexturefetch.cpp
@@ -483,12 +483,12 @@ private:
 	bool acquireHttpSemaphore()
 		{
 			llassert(! mHttpHasResource);
-			if (mFetcher->mHttpSemaphore <= 0)
+			if (mFetcher->mHttpSemaphore >= mFetcher->mHttpHighWater)
 			{
 				return false;
 			}
 			mHttpHasResource = true;
-			mFetcher->mHttpSemaphore--;
+			mFetcher->mHttpSemaphore++;
 			return true;
 		}
 
@@ -498,7 +498,8 @@ private:
 		{
 			llassert(mHttpHasResource);
 			mHttpHasResource = false;
-			mFetcher->mHttpSemaphore++;
+			mFetcher->mHttpSemaphore--;
+			llassert_always(mFetcher->mHttpSemaphore >= 0);
 		}
 	
 private:
@@ -2523,6 +2524,8 @@ LLTextureFetch::LLTextureFetch(LLTextureCache* cache, LLImageDecodeThread* image
 	mMaxBandwidth = gSavedSettings.getF32("ThrottleBandwidthKBPS");
 	mTextureInfo.setUpLogging(gSavedSettings.getBOOL("LogTextureDownloadsToViewerLog"), gSavedSettings.getBOOL("LogTextureDownloadsToSimulator"), U32Bytes(gSavedSettings.getU32("TextureLoggingThreshold")));
 
+	LLAppCoreHttp & app_core_http(LLAppViewer::instance()->getAppCoreHttp());
+	mHttpPolicyClass = app_core_http.getPolicy(LLAppCoreHttp::AP_TEXTURE);
 	mHttpRequest = new LLCore::HttpRequest;
 	mHttpOptions = new LLCore::HttpOptions;
 	mHttpOptionsWithHeaders = new LLCore::HttpOptions;
@@ -2531,21 +2534,9 @@ LLTextureFetch::LLTextureFetch(LLTextureCache* cache, LLImageDecodeThread* image
 	mHttpHeaders->append("Accept", "image/x-j2c");
 	mHttpMetricsHeaders = new LLCore::HttpHeaders;
 	mHttpMetricsHeaders->append("Content-Type", "application/llsd+xml");
-	LLAppCoreHttp & app_core_http(LLAppViewer::instance()->getAppCoreHttp());
-	mHttpPolicyClass = app_core_http.getPolicy(LLAppCoreHttp::AP_TEXTURE);
-	if (app_core_http.isPipelined(LLAppCoreHttp::AP_TEXTURE))
-	{
-		// Init-time election that will have to change for
-		// support of dynamic changes to the pipelining enable flag.
-		mHttpHighWater = HTTP_PIPE_REQUESTS_HIGH_WATER;
-		mHttpLowWater = HTTP_PIPE_REQUESTS_LOW_WATER;
-	}
-	else
-	{
-		mHttpHighWater = HTTP_NONPIPE_REQUESTS_HIGH_WATER;
-		mHttpLowWater = HTTP_NONPIPE_REQUESTS_LOW_WATER;
-	}
-	mHttpSemaphore = mHttpHighWater;
+	mHttpHighWater = HTTP_NONPIPE_REQUESTS_HIGH_WATER;
+	mHttpLowWater = HTTP_NONPIPE_REQUESTS_LOW_WATER;
+	mHttpSemaphore = 0;
 
 	// Conditionally construct debugger object after 'this' is
 	// fully initialized.
@@ -3032,6 +3023,20 @@ bool LLTextureFetch::runCondition()
 // Threads:  Ttf
 void LLTextureFetch::commonUpdate()
 {
+	// Update low/high water levels based on pipelining.  We pick
+	// up setting eventually, so the semaphore/request level can
+	// fall outside the [0..HIGH_WATER] range.  Expect that.
+	if (LLAppViewer::instance()->getAppCoreHttp().isPipelined(LLAppCoreHttp::AP_TEXTURE))
+	{
+		mHttpHighWater = HTTP_PIPE_REQUESTS_HIGH_WATER;
+		mHttpLowWater = HTTP_PIPE_REQUESTS_LOW_WATER;
+	}
+	else
+	{
+		mHttpHighWater = HTTP_NONPIPE_REQUESTS_HIGH_WATER;
+		mHttpLowWater = HTTP_NONPIPE_REQUESTS_LOW_WATER;
+	}
+
 	// Release waiters
 	releaseHttpWaiters();
 	
@@ -3693,8 +3698,16 @@ void LLTextureFetch::releaseHttpWaiters()
 {
 	// Use mHttpSemaphore rather than mHTTPTextureQueue.size()
 	// to avoid a lock.  
-	if (mHttpSemaphore < (mHttpHighWater - mHttpLowWater))
+	if (mHttpSemaphore >= mHttpLowWater)
 		return;
+	S32 needed(mHttpHighWater - mHttpSemaphore);
+	if (needed <= 0)
+	{
+		// Would only happen if High/LowWater were changed behind
+		// our back.  In that case, defer fill until usage falls within
+		// limits.
+		return;
+	}
 
 	// Quickly make a copy of all the LLUIDs.  Get off the
 	// mutex as early as possible.
@@ -3743,10 +3756,10 @@ void LLTextureFetch::releaseHttpWaiters()
 	tids.clear();
 
 	// Sort into priority order, if necessary and only as much as needed
-	if (tids2.size() > mHttpSemaphore)
+	if (tids2.size() > needed)
 	{
 		LLTextureFetchWorker::Compare compare;
-		std::partial_sort(tids2.begin(), tids2.begin() + mHttpSemaphore, tids2.end(), compare);
+		std::partial_sort(tids2.begin(), tids2.begin() + needed, tids2.end(), compare);
 	}
 
 	// Release workers up to the high water mark.  Since we aren't
-- 
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