[http] keep cache for TMethodCall objects

When exe.json executed for same method many times create TMethodCall once
and reuse it. Should significantly reduce memory fragmentation from cling and
probably avoid memory leaks.

Author: linev

net/httpsniff/inc/TRootSnifferFull.h

@@ -14,13 +14,18 @@
 
 #include "TRootSniffer.h"
 #include <string>
+#include <memory>
+#include <map>
 
 class TMemFile;
+class TMethodCall;
+class TMethod;
 
 class TRootSnifferFull : public TRootSniffer {
 protected:
    TMemFile *fMemFile{nullptr}; ///<! file used to manage streamer infos
    TList *fSinfo{nullptr};      ///<! last produced streamer info
+   std::map<const TMethod *, std::unique_ptr<TMethodCall>> fExeCache; ///<! cache for exe.json invocation
 
    void ScanObjectProperties(TRootSnifferScanRec &rec, TObject *obj) override;
 

net/httpsniff/src/TRootSnifferFull.cxx

@@ -825,20 +825,30 @@ Bool_t TRootSnifferFull::ProduceExe(const std::string &path, const std::string &
 
    if (method != nullptr) {
       if (can_use_plain) {
-         call = new TMethodCall();
-         call->InitWithPrototype(obj_cl, method_name, prototype.IsNull() ? nullptr : prototype.Data());
-      } else
+         // prevent creation of huge cache
+         if (fExeCache.size() > 1000)
+            fExeCache.clear();
+         auto iter = fExeCache.find(method);
+         if (iter != fExeCache.end()) {
+            call = iter->second.get();
+         } else {
+            call = new TMethodCall();
+            call->InitWithPrototype(obj_cl, method_name, prototype.IsNull() ? nullptr : prototype.Data());
+            fExeCache.emplace(method, std::unique_ptr<TMethodCall>(call));
+         }
+      } else {
          call = new TMethodCall(obj_cl, method_name, call_args.Data());
+         garbage.Add(call);
+      }
       if (debug)
          debug->append(TString::Format("Calling obj->%s(%s);\n", method_name, call_args.Data()).Data());
    } else {
       call = new TMethodCall(funcname.Data(), call_args.Data());
+      garbage.Add(call);
       if (debug)
          debug->append(TString::Format("Calling %s(%s);\n", funcname.Data(), call_args.Data()).Data());
    }
 
-   garbage.Add(call);
-
    if (!call->IsValid()) {
       if (debug)
          debug->append("Fail: invalid TMethodCall\n");