Add loadgen "stop" mode

docs/software/commands.md

@@ -471,7 +471,7 @@ this survey mechanism, just set `SURVEYOR_KEYS` to `$self` or a bogus key
 
 ### The following HTTP commands are exposed on test instances
 * **generateload** `generateload[?mode=
-    (create|pay|pretend|mixed_classic|soroban_upload|soroban_invoke_setup|soroban_invoke|upgrade_setup|create_upgrade|mixed_classic_soroban)&accounts=N&offset=K&txs=M&txrate=R&spikesize=S&spikeinterval=I&maxfeerate=F&skiplowfeetxs=(0|1)&dextxpercent=D&minpercentsuccess=S&instances=Y&wasms=Z&payweight=P&sorobanuploadweight=Q&sorobaninvokeweight=R]`
+    (create|pay|pretend|mixed_classic|soroban_upload|soroban_invoke_setup|soroban_invoke|upgrade_setup|create_upgrade|mixed_classic_soroban|stop)&accounts=N&offset=K&txs=M&txrate=R&spikesize=S&spikeinterval=I&maxfeerate=F&skiplowfeetxs=(0|1)&dextxpercent=D&minpercentsuccess=S&instances=Y&wasms=Z&payweight=P&sorobanuploadweight=Q&sorobaninvokeweight=R]`
 
     Artificially generate load for testing; must be used with
     `ARTIFICIALLY_GENERATE_LOAD_FOR_TESTING` set to true.
@@ -532,6 +532,7 @@ this survey mechanism, just set `SURVEYOR_KEYS` to `$self` or a bogus key
     `soroban_upload`, and `soroban_invoke` load with the likelihood of any
     generated transaction falling into each mode being determined by the mode's
     weight divided by the sum of all weights.
+  * `stop` mode stops any existing load generation run and marks it as "failed".
 
   Non-`create` load generation makes use of the additional parameters:
   * when a nonzero `spikeinterval` is given, a spike will occur every

src/main/CommandHandler.cpp

@@ -1263,9 +1263,18 @@ CommandHandler::generateLoad(std::string const& params, std::string& retStr)
     {
         std::map<std::string, std::string> map;
         http::server::server::parseParams(params, map);
+        auto modeStr =
+            parseOptionalParamOrDefault<std::string>(map, "mode", "create");
+        // First check if a current run needs to be stopped
+        if (modeStr == "stop")
+        {
+            mApp.getLoadGenerator().stop();
+            retStr = "Stopped load generation";
+            return;
+        }
+
         GeneratedLoadConfig cfg;
-        cfg.mode = LoadGenerator::getMode(
-            parseOptionalParamOrDefault<std::string>(map, "mode", "create"));
+        cfg.mode = LoadGenerator::getMode(modeStr);
 
         cfg.nAccounts =
             parseOptionalParamOrDefault<uint32_t>(map, "accounts", 1000);

src/simulation/LoadGenerator.cpp

@@ -276,6 +276,23 @@ LoadGenerator::resetSorobanState()
     mContactOverheadBytes = 0;
 }
 
+void
+LoadGenerator::stop()
+{
+    ZoneScoped;
+    if (mStarted)
+    {
+        // Some residual transactions might still be pending in consensus, but
+        // that should be harmless.
+        if (mLoadTimer)
+        {
+            mLoadTimer->cancel();
+        }
+        mLoadgenFail.Mark();
+        reset();
+    }
+}
+
 void
 LoadGenerator::start(GeneratedLoadConfig& cfg)
 {

src/simulation/LoadGenerator.h

@@ -205,6 +205,8 @@ class LoadGenerator
         return mContactOverheadBytes;
     }
 
+    void stop();
+
   private:
     struct TxMetrics
     {

src/simulation/test/LoadGeneratorTests.cpp

@@ -124,6 +124,26 @@ TEST_CASE("generate load with unique accounts", "[loadgen]")
             },
             10 * Herder::EXP_LEDGER_TIMESPAN_SECONDS, false);
     }
+    SECTION("stop loadgen")
+    {
+        loadGen.generateLoad(GeneratedLoadConfig::createAccountsLoad(
+            /* nAccounts */ 10000,
+            /* txRate */ 1));
+        simulation->crankForAtLeast(std::chrono::seconds(10), false);
+        auto& acc = app.getMetrics().NewMeter({"loadgen", "account", "created"},
+                                              "account");
+        auto numAccounts = acc.count();
+        REQUIRE(app.getMetrics()
+                    .NewMeter({"loadgen", "run", "failed"}, "run")
+                    .count() == 0);
+        loadGen.stop();
+        REQUIRE(app.getMetrics()
+                    .NewMeter({"loadgen", "run", "failed"}, "run")
+                    .count() == 1);
+        // No new txs submitted
+        simulation->crankForAtLeast(std::chrono::seconds(10), false);
+        REQUIRE(acc.count() == numAccounts);
+    }
 }
 
 TEST_CASE("modify soroban network config", "[loadgen][soroban]")