src: limit foreground tasks draining loop

Foreground tasks that repost themselves can force the draining loop
to run indefinitely long without giving other tasks chance to run.

This limits the foreground task draining loop to run only the tasks
that were in the tasks queue at the beginning of the loop.

PR-URL: https://github.com/nodejs/node/pull/19987
Fixes: https://github.com/nodejs/node/issues/19937
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yang Guo <yangguo@chromium.org>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Khaidi Chu <i@2333.moe>

1 files changed, 55 insertions, 0 deletions

diff --git a/test/cctest/test_platform.cc b/test/cctest/test_platform.cc
new file mode 100644
index 0000000000..876547480b
--- /dev/null
+++ b/test/cctest/test_platform.cc
@@ -0,0 +1,55 @@
+#include "node_internals.h"
+#include "libplatform/libplatform.h"
+
+#include <string>
+#include "gtest/gtest.h"
+#include "node_test_fixture.h"
+
+// This task increments the given run counter and reposts itself until the
+// repost counter reaches zero.
+class RepostingTask : public v8::Task {
+ public:
+  explicit RepostingTask(int repost_count,
+                         int* run_count,
+                         v8::Isolate* isolate,
+                         node::NodePlatform* platform)
+      : repost_count_(repost_count),
+        run_count_(run_count),
+        isolate_(isolate),
+        platform_(platform) {}
+
+  // v8::Task implementation
+  void Run() final {
+    ++*run_count_;
+    if (repost_count_ > 0) {
+      --repost_count_;
+      platform_->CallOnForegroundThread(isolate_,
+          new RepostingTask(repost_count_, run_count_, isolate_, platform_));
+    }
+  }
+
+ private:
+  int repost_count_;
+  int* run_count_;
+  v8::Isolate* isolate_;
+  node::NodePlatform* platform_;
+};
+
+class PlatformTest : public EnvironmentTestFixture {};
+
+TEST_F(PlatformTest, SkipNewTasksInFlushForegroundTasks) {
+  v8::Isolate::Scope isolate_scope(isolate_);
+  const v8::HandleScope handle_scope(isolate_);
+  const Argv argv;
+  Env env {handle_scope, argv};
+  int run_count = 0;
+  platform->CallOnForegroundThread(
+      isolate_, new RepostingTask(2, &run_count, isolate_, platform.get()));
+  EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
+  EXPECT_EQ(1, run_count);
+  EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
+  EXPECT_EQ(2, run_count);
+  EXPECT_TRUE(platform->FlushForegroundTasks(isolate_));
+  EXPECT_EQ(3, run_count);
+  EXPECT_FALSE(platform->FlushForegroundTasks(isolate_));
+}