Add --force-gc support (#248)

Call globalThis.gc() before every benchmark to help debug cross-workload leaks.

Author: camillobruni

JetStreamDriver.js

@@ -30,8 +30,13 @@ const measureTotalTimeAsSubtest = false; // Once we move to preloading all resou
 const defaultIterationCount = 120;
 const defaultWorstCaseCount = 4;
 
-if (!JetStreamParams.prefetchResources && isInBrowser)
+if (!JetStreamParams.prefetchResources && isInBrowser) {
     console.warn("Disabling resource prefetching! All compressed files must have been decompressed using `npm run decompress`");
+}
+
+if (JetStreamParams.forceGC && typeof globalThis.gc === "undefined") {
+    console.warn("Force-gc is set, but globalThis.gc() is not available.");
+}
 
 if (!isInBrowser && JetStreamParams.prefetchResources) {
     // Use the wasm compiled zlib as a polyfill when decompression stream is
@@ -913,6 +918,14 @@ class Benchmark {
         if (this.isDone)
             throw new Error(`Cannot run Benchmark ${this.name} twice`);
         this._state = BenchmarkState.PREPARE;
+
+        if (JetStreamParams.forceGC) {
+            // This will trigger for individual benchmarks in
+            // GroupedBenchmarks since they delegate .run() to their inner
+            // non-grouped benchmarks.
+            globalThis?.gc();
+        }
+
         const scripts = isInBrowser ? new BrowserScripts(this.preloads) : new ShellScripts(this.preloads);
 
         if (!!this.plan.deterministicRandom)

cli.js

@@ -81,6 +81,10 @@ const CLI_PARAMS = {
     help: "Custom code to run after each iteration.",
     param: "customPostIterationCode",
   },
+  "force-gc": {
+    help: "Force garbage collection before each benchmark, requires engine support.",
+    param: "forceGC",
+  },
 };
 
 const cliParams = new Map();

utils/params.js

@@ -43,6 +43,7 @@ class Params {
     groupDetails = false
 
     RAMification = false;
+    forceGC = false;
     dumpJSONResults = false;
     dumpTestList = false;
     // Override iteration and worst-case counts per workload.
@@ -70,6 +71,7 @@ class Params {
         this.dumpJSONResults = this._parseBooleanParam(sourceParams, "dumpJSONResults");
         this.groupDetails = this._parseBooleanParam(sourceParams, "groupDetails");
         this.dumpTestList = this._parseBooleanParam(sourceParams, "dumpTestList");
+        this.forceGC = this._parseBooleanParam(sourceParams, "forceGC");
 
         this.customPreIterationCode = this._parseStringParam(sourceParams, "customPreIterationCode");
         this.customPostIterationCode = this._parseStringParam(sourceParams, "customPostIterationCode");