test.cpp

#include <chrono>
#include <thread>
#include <Windows.h>

int __stdcall wWinMain(HINSTANCE, HINSTANCE, PWSTR, int) {
  {
    std::jthread a([]() {
      std::this_thread::sleep_for(std::chrono::seconds(1));
      if (HeapLock(GetProcessHeap())) {
        OutputDebugStringA("Locked heap in A\n");
      }
      std::this_thread::sleep_for(std::chrono::seconds(10));
      OutputDebugStringA("About to unlock heap in A\n");
      if (HeapUnlock(GetProcessHeap())) {
        OutputDebugStringA("Unlocked heap in A\n");
      } else {
        OutputDebugStringA("Failed to unlock heap in A\n");
      }
    });
    std::jthread b([]() {
      std::this_thread::sleep_for(std::chrono::seconds(2));
      if (HeapUnlock(GetProcessHeap())) {
        OutputDebugStringA("Unlocked in B\n");
      } else {
        OutputDebugStringA("Failed to unlock in B\n");
      }
      if (HeapLock(GetProcessHeap())) {
        OutputDebugStringA("Locked in B\n");
        HeapUnlock(GetProcessHeap());
      }
    });
    std::jthread c([]() {
      std::this_thread::sleep_for(std::chrono::seconds(3));
      HeapLock(GetProcessHeap());
      OutputDebugStringA("Locked in C\n");
      HeapUnlock(GetProcessHeap());
    });
  }
  OutputDebugStringA("Finished all threads\n");
  return 0;
}

test.out

Locked heap in A
Unlocked in B
Locked in B
Locked in C
About to unlock heap in A
Unlocked heap in A
Finished all threads