From 02d00265e71b9739b48c2f2f9a9089f4b5f2b363 Mon Sep 17 00:00:00 2001
From: Doug Gale <doug65536@gmail.com>
Date: Fri, 26 Dec 2014 02:27:09 -0500
Subject: [PATCH] Initial implementation

---
 CMakeLists.txt |   2 +
 main.cpp       | 153 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 155 insertions(+)
 create mode 100644 CMakeLists.txt
 create mode 100644 main.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..38e7a7c
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,2 @@
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -pthread")
+add_executable(starve-check main.cpp)
diff --git a/main.cpp b/main.cpp
new file mode 100644
index 0000000..3e3cc04
--- /dev/null
+++ b/main.cpp
@@ -0,0 +1,153 @@
+
+#include <iostream>
+#include <algorithm>
+#include <cstring>
+#include <thread>
+#include <atomic>
+#include <chrono>
+#include <mutex>
+#include <condition_variable>
+#include <unordered_map>
+
+static constexpr std::size_t max_threads = 256;
+
+typedef std::chrono::system_clock Clock;
+typedef std::chrono::time_point<Clock> TimePoint;
+typedef std::chrono::duration<double> Duration;
+
+static void error(char const* message, int exitcode = 2)
+{
+    std::cerr << message << std::endl;
+    exit(exitcode);
+}
+
+class stress_instance
+{
+public:
+    stress_instance();
+    ~stress_instance();
+    void run();
+    std::int64_t getCount();
+    void stop();
+
+private:
+    typedef std::atomic_int_least64_t CounterType;
+    void worker();
+
+    std::atomic_bool stopRequested;
+    std::thread thread;
+    char padding1[64];
+    CounterType counter;
+    char padding2[64];
+};
+
+static int run_stress(int cpucount, int timeLimit)
+{
+    static stress_instance instances[max_threads];
+    stress_instance* end = instances + cpucount;
+    std::for_each(instances, end,
+    [](stress_instance& instance)
+    {
+        instance.run();
+    });
+
+    // Use a condition variable wait for delays
+    // It looks more like we are doing work than
+    // it would if we were calling sleep_for
+    std::mutex dummyMutex;
+    std::condition_variable dummyConditionVariable;
+    std::unique_lock<std::mutex> lock(dummyMutex);
+    do
+    {
+        dummyConditionVariable.wait_until(lock, Clock::now() + Duration(1));
+
+        std::for_each(instances, end,
+        [](stress_instance& instance)
+        {
+            std::cout << (instance.getCount() / 1000000) << "M ";
+        });
+        std::cout << std::endl;
+
+        // Only decrement it if it is positive
+        timeLimit -= (timeLimit > 0);
+    }
+    while (timeLimit != 0);
+}
+
+int main(int argc, char** argv)
+{
+    int threads = 1;
+    bool force = false;
+    int timeLimit = -1;
+
+    for (int i = 1; i < argc; )
+    {
+        if (!strcmp(argv[i], "-t"))
+        {
+            if (argc + 1 >= argc)
+                error("Missing argument to thread count option (-t)");
+            threads = atoi(argv[++i]);
+        }
+        else if (!strcmp(argv[i], "-i"))
+        {
+            if (argc + 1 >= argc)
+                error("Missing argument to iteration count option (-i)");
+            timeLimit = atoi(argv[++i]);
+        }
+        else if (!strcmp(argv[i], "-f"))
+        {
+            force = true;
+        }
+        else
+        {
+            error((std::string("Invalid switch: ") + argv[i]).c_str());
+        }
+    }
+
+    std::size_t cpuCount = std::thread::hardware_concurrency();
+
+    if (threads <= 0)
+        threads = cpuCount;
+
+    if (!force && threads > cpuCount)
+        threads = cpuCount;
+
+    if (threads > max_threads)
+        threads = max_threads;
+
+    return run_stress(threads, timeLimit);
+}
+
+stress_instance::stress_instance()
+    : stopRequested(false)
+    , counter(0)
+{
+}
+
+stress_instance::~stress_instance()
+{
+    stop();
+}
+
+void stress_instance::run()
+{
+    thread = std::thread(&stress_instance::worker, this);
+}
+
+std::int64_t stress_instance::getCount()
+{
+    return counter.exchange(0);
+}
+
+void stress_instance::stop()
+{
+    stopRequested = true;
+    if (thread.joinable())
+        thread.join();
+}
+
+void stress_instance::worker()
+{
+    while (!stopRequested)
+        ++counter;
+}