Extend createjoinsplit to benchmark parallel JoinSplits

Closes #1940

qa/zcash/performance-measurements.sh

@@ -74,7 +74,7 @@ case "$1" in
                 zcash_rpc zcbenchmark parameterloading 10
                 ;;
             createjoinsplit)
-                zcash_rpc zcbenchmark createjoinsplit 10
+                zcash_rpc zcbenchmark createjoinsplit 10 "${@:3}"
                 ;;
             verifyjoinsplit)
                 zcash_rpc zcbenchmark verifyjoinsplit 1000 "\"$RAWJOINSPLIT\""
@@ -111,7 +111,7 @@ case "$1" in
                 zcash_rpc zcbenchmark parameterloading 1
                 ;;
             createjoinsplit)
-                zcash_rpc zcbenchmark createjoinsplit 1
+                zcash_rpc zcbenchmark createjoinsplit 1 "${@:3}"
                 ;;
             verifyjoinsplit)
                 zcash_rpc zcbenchmark verifyjoinsplit 1 "\"$RAWJOINSPLIT\""
@@ -146,7 +146,7 @@ case "$1" in
                 zcash_rpc zcbenchmark parameterloading 1
                 ;;
             createjoinsplit)
-                zcash_rpc zcbenchmark createjoinsplit 1
+                zcash_rpc zcbenchmark createjoinsplit 1 "${@:3}"
                 ;;
             verifyjoinsplit)
                 zcash_rpc zcbenchmark verifyjoinsplit 1 "\"$RAWJOINSPLIT\""

src/wallet/rpcwallet.cpp

@@ -2465,7 +2465,15 @@ Value zc_benchmark(const json_spirit::Array& params, bool fHelp)
         } else if (benchmarktype == "parameterloading") {
             sample_times.push_back(benchmark_parameter_loading());
         } else if (benchmarktype == "createjoinsplit") {
-            sample_times.push_back(benchmark_create_joinsplit());
+            if (params.size() < 3) {
+                sample_times.push_back(benchmark_create_joinsplit());
+            } else {
+                int nThreads = params[2].get_int();
+                std::vector<double> vals = benchmark_create_joinsplit_threaded(nThreads);
+                // Divide by nThreads^2 to get average seconds per JoinSplit because
+                // we are running one JoinSplit per thread.
+                sample_times.push_back(std::accumulate(vals.begin(), vals.end(), 0.0) / (nThreads*nThreads));
+            }
         } else if (benchmarktype == "verifyjoinsplit") {
             sample_times.push_back(benchmark_verify_joinsplit(samplejoinsplit));
         } else if (benchmarktype == "solveequihash") {

src/zcbenchmarks.cpp

@@ -95,6 +95,27 @@ double benchmark_create_joinsplit()
     return ret;
 }
 
+std::vector<double> benchmark_create_joinsplit_threaded(int nThreads)
+{
+    std::vector<double> ret;
+    std::vector<std::future<double>> tasks;
+    std::vector<std::thread> threads;
+    for (int i = 0; i < nThreads; i++) {
+        std::packaged_task<double(void)> task(&benchmark_create_joinsplit);
+        tasks.emplace_back(task.get_future());
+        threads.emplace_back(std::move(task));
+    }
+    std::future_status status;
+    for (auto it = tasks.begin(); it != tasks.end(); it++) {
+        it->wait();
+        ret.push_back(it->get());
+    }
+    for (auto it = threads.begin(); it != threads.end(); it++) {
+        it->join();
+    }
+    return ret;
+}
+
 double benchmark_verify_joinsplit(const JSDescription &joinsplit)
 {
     struct timeval tv_start;

src/zcbenchmarks.h

@@ -7,6 +7,7 @@
 extern double benchmark_sleep();
 extern double benchmark_parameter_loading();
 extern double benchmark_create_joinsplit();
+extern std::vector<double> benchmark_create_joinsplit_threaded(int nThreads);
 extern double benchmark_solve_equihash();
 extern std::vector<double> benchmark_solve_equihash_threaded(int nThreads);
 extern double benchmark_verify_joinsplit(const JSDescription &joinsplit);