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WebSocket property-mirror: optimise JSON building

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Work around some awful cJSON performance when building large arrays,
greatly speeding up remote-canvas updating
This commit is contained in:
James Turner 2018-06-24 23:20:19 +01:00
parent b2e8097b22
commit 7d84a03dea
1 changed files with 35 additions and 11 deletions
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46
src/Network/http/MirrorPropertyTreeWebsocket.cxx
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@ -140,7 +140,6 @@ using std::string;
virtual ~MirrorTreeListener()
{
SG_LOG(SG_NETWORK, SG_INFO, "destroying MirrorTreeListener");
}
virtual void valueChanged(SGPropertyNode* node) override
@ -224,18 +223,23 @@ using std::string;
cJSON* makeJSONData()
{
#if defined (MIRROR_DEBUG)
SGTimeStamp st;
st.stamp();
cJSON* result = cJSON_CreateObject();
int newSize = newNodes.size();
int changedSize = changedNodes.size();
int removedSize = removedNodes.size();
#endif
cJSON* result = cJSON_CreateObject();
if (!newNodes.empty()) {
cJSON * newNodesArray = cJSON_CreateArray();
// cJSON_AddItemToArray performance is O(N) due to use of a linked
// list, which dominates the performance here. To fix this we maintan
// a point to the tail of the array, keeping appends O(1)
cJSON* arrayTail = nullptr;
for (auto prop : newNodes) {
changedNodes.erase(prop); // avoid duplicate send
cJSON* newPropData = cJSON_CreateObject();
@ -247,7 +251,15 @@ using std::string;
if (prop->getType() != simgear::props::NONE) {
cJSON_AddItemToObject(newPropData, "value", JSON::valueToJson(prop));
}
cJSON_AddItemToArray(newNodesArray, newPropData);
if (arrayTail) {
arrayTail->next = newPropData;
newPropData->prev = arrayTail;
arrayTail = newPropData;
} else {
cJSON_AddItemToArray(newNodesArray, newPropData);
arrayTail = newPropData;
}
}
newNodes.clear();
@ -266,19 +278,32 @@ using std::string;
if (!changedNodes.empty()) {
cJSON * changedNodesArray = cJSON_CreateArray();
// see comment above about cJSON_AddItemToArray
cJSON* tail = nullptr;
for (auto prop : changedNodes) {
cJSON* propData = cJSON_CreateArray();
cJSON_AddItemToArray(propData, cJSON_CreateNumber(idForProperty(prop)));
cJSON_AddItemToArray(propData, JSON::valueToJson(prop));
cJSON_AddItemToArray(changedNodesArray, propData);
if (tail) {
tail->next = propData;
propData->prev = tail;
tail = propData;
} else {
cJSON_AddItemToArray(changedNodesArray, propData);
tail = propData;
}
}
changedNodes.clear();
cJSON_AddItemToObject(result, "changed", changedNodesArray);
}
#if defined (MIRROR_DEBUG)
SG_LOG(SG_NETWORK, SG_INFO, "making JSON data took:" << st.elapsedMSec() << " for " << newSize << "/" << changedSize << "/" << removedSize);
#endif
recentlyRemoved.clear();
return result;
@ -366,7 +391,6 @@ MirrorPropertyTreeWebsocket::MirrorPropertyTreeWebsocket(const std::string& path
MirrorPropertyTreeWebsocket::~MirrorPropertyTreeWebsocket()
{
SG_LOG(SG_NETWORK, SG_INFO, "shutting down MirrorPropertyTreeWebsocket");
}
void MirrorPropertyTreeWebsocket::close()