First 'crash free' version.

This version runs through our initial fft and fib tests. However, it is not tested further in any way. Additionally, we added a locking deque, potentially hurting performance and moving away from our initial goal.

app/benchmark_fft/main.cpp

@@ -90,8 +90,8 @@ complex_vector prepare_input(int input_size) {
   return data;
 }
 
-static constexpr int NUM_ITERATIONS = 1000;
-constexpr size_t NUM_THREADS = 2;
+static constexpr int NUM_ITERATIONS = 500;
+constexpr size_t NUM_THREADS = 8;
 
 constexpr size_t NUM_TASKS = 128;
 constexpr size_t MAX_TASK_STACK_SIZE = 0;
@@ -127,14 +127,14 @@ int main() {
   std::cout << "Framework:  " << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
             << std::endl;
 
-  start = std::chrono::steady_clock::now();
-  for (int i = 0; i < NUM_ITERATIONS; i++) {
-    complex_vector input_1(initial_input);
-    fft_normal(input_1.begin(), INPUT_SIZE);
-  }
-  end = std::chrono::steady_clock::now();
-  std::cout << "Normal:     " << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
-            << std::endl;
+//  start = std::chrono::steady_clock::now();
+//  for (int i = 0; i < NUM_ITERATIONS; i++) {
+//    complex_vector input_1(initial_input);
+//    fft_normal(input_1.begin(), INPUT_SIZE);
+//  }
+//  end = std::chrono::steady_clock::now();
+//  std::cout << "Normal:     " << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
+//            << std::endl;
 
   return 0;
 }

lib/pls/CMakeLists.txt

@@ -58,7 +58,7 @@ add_library(pls STATIC
         include/pls/internal/scheduling/task.h src/internal/scheduling/task.cpp
         include/pls/internal/scheduling/cont_manager.h
         include/pls/internal/scheduling/cont.h
-        include/pls/internal/data_structures/bounded_ws_deque.h include/pls/internal/data_structures/optional.h include/pls/internal/scheduling/memory_block.h include/pls/internal/scheduling/thread_state_static.h)
+        include/pls/internal/data_structures/bounded_ws_deque.h include/pls/internal/data_structures/optional.h include/pls/internal/scheduling/memory_block.h include/pls/internal/scheduling/thread_state_static.h src/internal/base/error_handling.cpp)
 
 # Add everything in `./include` to be in the include path of this project
 target_include_directories(pls

lib/pls/include/pls/internal/base/error_handling.h

@@ -12,6 +12,9 @@
  * (or its inclusion adds too much overhead).
  */
 #define PLS_ERROR(msg) printf("%s\n", msg); exit(1);
-#define PLS_ASSERT(cond, msg) if (!(cond)) { PLS_ERROR(msg) }
+
+void pls_error(const char *msg);
+
+#define PLS_ASSERT(cond, msg) if (!(cond)) { pls_error(msg); }
 
 #endif //PLS_ERROR_HANDLING_H

lib/pls/include/pls/internal/data_structures/delayed_initialization.h

@@ -43,9 +43,7 @@ class delayed_initialization {
 
   template<typename ...ARGS>
   void initialize(ARGS &&...args) {
-    if (initialized_) {
-      PLS_ASSERT(!initialized_, "Can only initialize delayed wrapper object once!");
-    }
+    PLS_ASSERT(!initialized_, "Can only initialize delayed wrapper object once!");
 
     new((void *) memory_.data()) T(std::forward<ARGS>(args)...);
     initialized_ = true;
@@ -59,9 +57,8 @@ class delayed_initialization {
   }
 
   T &object() {
-    if (!initialized_) {
-      PLS_ASSERT(initialized_, "Can not use an uninitialized delayed wrapper object!")
-    }
+    PLS_ASSERT(initialized_, "Can not use an uninitialized delayed wrapper object!");
+
     return *reinterpret_cast<T *>(memory_.data());
   }
 

lib/pls/include/pls/internal/scheduling/cont.h

@@ -9,6 +9,7 @@
 #include "pls/internal/data_structures/stamped_integer.h"
 #include "pls/internal/data_structures/delayed_initialization.h"
 #include "pls/internal/base/alignment.h"
+#include "pls/internal/base/error_handling.h"
 
 #include "parallel_result.h"
 #include "memory_block.h"
@@ -28,7 +29,10 @@ class base_cont {
   explicit base_cont(base_cont *parent, memory_block *memory_block, bool is_right_child)
       : parent_{parent},
         memory_block_{memory_block},
-        is_right_child_{is_right_child} {};
+        is_right_child_{is_right_child} {
+    PLS_ASSERT(parent_ == nullptr || parent_->memory_block_->get_depth() == memory_block_->get_depth() - 1,
+               "Must only build cont chains with matching depth!")
+  };
 
   /**
    * Execute the continuation itself.
@@ -77,7 +81,8 @@ class cont : public base_cont {
     using BASE_RES_TYPE = typename std::remove_cv<typename std::remove_reference<RES_TYPE>::type>::type;
 
     static void execute(cont &cont) {
-      parallel_result<BASE_RES_TYPE> result{cont.function_((*cont.left_result_).value(), (*cont.right_result_).value())};
+      parallel_result<BASE_RES_TYPE>
+          result{cont.function_((*cont.left_result_).value(), (*cont.right_result_).value())};
       if (result.fast_path() && cont.parent_ != nullptr) {
         if (cont.is_right_child()) {
           cont.parent_->store_right_result(std::move(result));

lib/pls/include/pls/internal/scheduling/cont_manager.h

@@ -47,11 +47,11 @@ class cont_manager {
   }
   void move_active_node(int depth) {
     if (depth < 0) {
-      for (int i = 0; i < (depth * -1); i++) {
+      for (long i = 0; i < (depth * -1); i++) {
         active_node_ = active_node_->get_prev();
       }
     } else {
-      for (int i = 0; i < depth; i++) {
+      for (long i = 0; i < depth; i++) {
         active_node_ = active_node_->get_next();
       }
     }
@@ -88,49 +88,10 @@ class cont_manager {
 
     // Copy fall through status and reset it (for potentially nested execution paths).
     auto *notified_cont = fall_through_cont_;
-    bool notifier_is_right_child = fall_through_child_right;
-
-//    std::cout << "Notifying Cont on core " << my_state.get_id() << " and depth "
-//              << notified_cont->get_memory_block()->get_depth() << std::endl;
 
     fall_through_cont_ = nullptr;
     fall_through_ = false;
 
-    // Special case for lock free implementation.
-    // When we finish a 'left strain' it can happen that the 'right strain'
-    // is currently being stolen. We need to be sure that this steal is finished
-    // as we need the thieves memory blocks in case we get blocked by it.
-    if (!notifier_is_right_child) {
-      // Check to execute right child directly...
-      auto &atomic_state = notified_cont->get_memory_block()->get_state();
-      auto old_state = atomic_state.load();
-      memory_block::stamped_state target_state{old_state.stamp + 1, memory_block::state::execute_local};
-      memory_block::stamped_state exchanged_state = atomic_state.exchange(target_state);
-      if (exchanged_state.value != memory_block::state::stolen) {
-        // We 'overruled' the stealing thread and execute the other task ourselfs.
-        // We can be sure that only we where involved in executing the child tasks of the parent_continuation...
-        notified_cont->get_memory_block()->get_results_missing().fetch_add(-1);
-
-        my_state.parent_cont_ = notified_cont;
-        my_state.right_spawn_ = true;
-        notified_cont->execute_task();
-        if (falling_through()) {
-          // ... if the second strain was interrupted we fall through without scheduling the parent_continuation
-          // (the currently pending/interrupted strain will do this itself).
-          return;
-        } else {
-          // ... we could finish the second strain.
-          // Register the parent continuation for being notified.
-          // (This is not the most efficient, as we could simply execute it. However,
-          // this way of doing it spares us from duplicating a lot of code).
-          fall_through_and_notify_cont(notified_cont, true);
-          return;
-        }
-      }
-
-      // Right side is 'fully' stolen. We can continue to inform the parent like we would do normally.
-    }
-
     // Keep the target chain before we execute, as this potentially frees the memory
     auto *target_chain = notified_cont->get_memory_block()->get_offered_chain().load();
 
@@ -145,12 +106,10 @@ class cont_manager {
         // We do not own the thing we will execute.
         // Own it by swapping the chain belonging to it in.
         aquire_memory_chain(notified_cont->get_memory_block());
-//        std::cout << "Now in charge of memory chain on core " << my_state.get_id() << std::endl;
       }
       my_state.parent_cont_ = notified_cont->get_parent();
       my_state.right_spawn_ = notified_cont->is_right_child();
       active_node_ = notified_cont->get_memory_block();
-//      std::cout << "Execute cont on core " << my_state.get_id() << std::endl;
       notified_cont->execute();
       if (!falling_through() && notified_cont->get_parent() != nullptr) {
         fall_through_and_notify_cont(notified_cont->get_parent(), notified_cont->is_right_child());
@@ -166,7 +125,6 @@ class cont_manager {
         // We own the thing we are not allowed to execute.
         // Get rid of the ownership by using the offered chain.
         aquire_memory_chain(target_chain);
-//        std::cout << "No longer in charge of chain above on core " << my_state.get_id() << std::endl;
       }
 
       move_active_node_to_start();

lib/pls/include/pls/internal/scheduling/memory_block.h

@@ -19,7 +19,7 @@ class memory_block {
   memory_block(char *memory_buffer,
                size_t memory_buffer_size,
                memory_block *prev,
-               unsigned int depth)
+               int depth)
       : prev_{prev},
         next_{nullptr},
         offered_chain_{nullptr},
@@ -32,10 +32,7 @@ class memory_block {
 
   template<typename T, typename ...ARGS>
   T *place_in_buffer(ARGS &&...args) {
-    if (memory_buffer_used_) {
-      pls::internal::base::this_thread::sleep(100000);
-      PLS_ASSERT(!memory_buffer_used_, "Must only allocate one continuation at once per node.");
-    }
+    PLS_ASSERT(!memory_buffer_used_, "Must only allocate one continuation at once per node.");
 
     memory_buffer_used_ = true;
     return new(memory_buffer_) T(std::forward<ARGS>(args)...);
@@ -84,7 +81,7 @@ class memory_block {
     return results_missing_;
   }
 
-  unsigned int get_depth() const noexcept {
+  int get_depth() const noexcept {
     return depth_;
   }
 
@@ -130,7 +127,7 @@ class memory_block {
   // Each element stays at a fixed depth for the entire application run.
   // Swapping parts of a memory chain will not reorder it, as always parts of
   // the same size are exchanged.
-  const unsigned int depth_;
+  const int depth_;
 };
 
 }

lib/pls/include/pls/internal/scheduling/task_manager.h

@@ -56,6 +56,9 @@ class task_manager {
   // Returns a pair containing the actual task and if the steal was successful.
   base_task *steal_remote_task(cont_manager &stealing_cont_manager) {
     std::lock_guard<base::spin_lock> lock{lock_};
+
+    // TODO: See if we can somehow make this trade lock free (and still be correct)
+
     auto stolen_task_handle = task_deque_.pop_top();
     if (stolen_task_handle) {
       base_task *stolen_task = (*stolen_task_handle).task_;
@@ -64,50 +67,14 @@ class task_manager {
       auto &atomic_state = stolen_task_memory->get_state();
       auto &atomic_offered_chain = stolen_task_memory->get_offered_chain();
 
-//      std::cout << "Nearly stole on core " << thread_state::get().get_id() << " task with depth "
-//                << stolen_task_depth << std::endl;
-
-      // Move our chain forward for stealing...
+      // TODO: We ignore all we tried with lock free implementations here, just store the state how it is supposed to be
       stealing_cont_manager.move_active_node(stolen_task_depth);
       auto offered_chain = stealing_cont_manager.get_active_node();
+      stealing_cont_manager.move_active_node(1);
+      atomic_offered_chain.store(offered_chain);
+      atomic_state.store(memory_block::stolen);
 
-      if (offered_chain == (*stolen_task_handle).task_memory_block_) {
-        PLS_ASSERT(false, "How would we offer our own chain? We only offer when stealing!");
-      }
-
-      auto last_state = atomic_state.load();
-      if (last_state.value != memory_block::initialized) {
-        stealing_cont_manager.move_active_node(-stolen_task_depth);
-        return nullptr;
-      }
-
-      auto last_offered_chain = atomic_offered_chain.load();
-      memory_block::stamped_state loop_state = {last_state.stamp + 1, memory_block::stealing};
-
-      if (atomic_state.compare_exchange_strong(last_state, loop_state)) {
-        while (true) {
-          if (atomic_offered_chain.compare_exchange_strong(last_offered_chain, offered_chain)) {
-            break;
-          }
-
-          last_offered_chain = atomic_offered_chain.load();
-          last_state = atomic_state.load();
-          if (last_state != loop_state) {
-            stealing_cont_manager.move_active_node(-stolen_task_depth);
-            return nullptr;
-          }
-        }
-
-        if (atomic_state.compare_exchange_strong(loop_state, {loop_state.stamp + 1, memory_block::stolen})) {
-//          std::cout << "Steal!" << std::endl;
-          stealing_cont_manager.move_active_node(1);
-          return stolen_task;
-        } else {
-          return nullptr;
-        }
-      } else {
-        return nullptr;
-      }
+      return stolen_task;
     } else {
       return nullptr;
     }

lib/pls/include/pls/internal/scheduling/thread_state.h

@@ -44,7 +44,12 @@ struct alignas(base::system_details::CACHE_LINE_SIZE) thread_state {
       task_manager_{task_manager},
       cont_manager_{cont_manager},
       current_task_{nullptr},
-      random_{static_cast<unsigned long>(std::chrono::steady_clock::now().time_since_epoch().count())} {}
+      random_{static_cast<unsigned long>(std::chrono::steady_clock::now().time_since_epoch().count())} {};
+
+  void reset() {
+    right_spawn_ = false;
+    parent_cont_ = nullptr;
+  }
 
   /**
    * Convenience helper to get the thread_state instance associated with this thread.

lib/pls/src/internal/base/error_handling.cpp

+#include "pls/internal/base/error_handling.h"
+
+void pls_error(const char *msg) {
+  PLS_ERROR(msg);
+}

lib/pls/src/internal/scheduling/scheduler.cpp

@@ -54,6 +54,7 @@ void scheduler::work_thread_main_loop() {
 
 void scheduler::work_thread_work_section() {
   auto &my_state = thread_state::get();
+  my_state.reset();
   auto &my_cont_manager = my_state.get_cont_manager();
 
   auto const num_threads = my_state.get_scheduler().num_threads();