WIP: Add simple external trading deque test.

The current version has race conditions and is hard to debug (especially because of the fibers, if a wrong thread executes on a fiber we get segfalts very fast). To combat this mess we now refactor the code bit by bit while also adding tests where it can be done with reasonably effort).

app/benchmark_fib/main.cpp

@@ -32,8 +32,8 @@ int pls_fib(int n) {
 }
 
 constexpr int MAX_NUM_THREADS = 4;
-constexpr int MAX_NUM_TASKS = 64;
-constexpr int MAX_STACK_SIZE = 4096 * 8;
+constexpr int MAX_NUM_TASKS = 32;
+constexpr int MAX_STACK_SIZE = 1024 * 32;
 
 static_scheduler_memory<MAX_NUM_THREADS,
                         MAX_NUM_TASKS,
@@ -48,7 +48,7 @@ int main(int argc, char **argv) {
   string full_directory = directory + "/PLS_v3/";
   benchmark_runner runner{full_directory, test_name};
 
-  scheduler scheduler{global_scheduler_memory, (unsigned) num_threads};
+  scheduler scheduler{global_scheduler_memory, (unsigned) num_threads, false};
 
   volatile int res;
   scheduler.perform_work([&]() {
@@ -58,7 +58,7 @@ int main(int argc, char **argv) {
   });
 
   scheduler.perform_work([&]() {
-    for (int i = 0; i < fib::NUM_ITERATIONS; i++) {
+    for (int i = 0; i < fib::NUM_ITERATIONS * 100; i++) {
       runner.start_iteration();
       res = pls_fib(fib::INPUT_N);
       runner.end_iteration();

app/playground/main.cpp

 #include <utility>
 #include <cstdio>
-#include <chrono>
 
 #include "context_switcher/context_switcher.h"
 using namespace context_switcher;
 using namespace std;
 
-const size_t NUM_RUNS = 1000;
-
 // Memory for custom stack and continuation semantics
-const size_t STACK_SIZE = 512 * 1;
-const size_t NUM_STACKS = 64;
+const size_t STACK_SIZE = 512 * 16;
+const size_t NUM_STACKS = 4;
 char custom_stacks[NUM_STACKS][STACK_SIZE];
 
-int fib(int n) {
-  if (n <= 1) {
-    return 1;
-  }
+volatile int result;
 
-  int a, b;
-  enter_context(custom_stacks[n], STACK_SIZE, [n, &a](continuation &&cont) {
-    a = fib(n - 1);
-    return std::move(cont);
-  });
-  enter_context(custom_stacks[n], STACK_SIZE, [n, &b](continuation &&cont) {
-    b = fib(n - 2);
-    return std::move(cont);
-  });
+int main() {
+  context_switcher::continuation outer_cont = enter_context(custom_stacks[0], STACK_SIZE, [](continuation &&main_cont) {
+    enter_context(custom_stacks[1], STACK_SIZE, [&main_cont](continuation &&middle_cont) {
+      enter_context(custom_stacks[2], STACK_SIZE, [&main_cont](continuation &&inner_cont) {
+        for (int i = 0; i < 10; i++) {
+          printf("Inner %d\n", i);
+          main_cont = context_switcher::switch_context(std::move(main_cont));
+        }
 
-  return a + b;
-}
+        return std::move(inner_cont);
+      });
 
-volatile int result;
-int main() {
-  auto start_time = chrono::steady_clock::now();
-  for (unsigned int i = 0; i < NUM_RUNS; i++) {
-    result = fib(18);
-  }
-  auto end_time = chrono::steady_clock::now();
-  auto time = chrono::duration_cast<chrono::microseconds>(end_time - start_time).count();
+      return std::move(middle_cont);
+    });
 
-  printf("%f", (float) time / NUM_RUNS);
+    return std::move(main_cont);
+  });
+
+  for (int i = 0; i < 10; i++) {
+    printf("Outer %d\n", i);
+    outer_cont = context_switcher::switch_context(std::move(outer_cont));
+  }
 
   return 0;
 }

lib/context_switcher/asm/enter_context_x86_64.s

@@ -17,10 +17,11 @@ __cs_enter_context:
         # Variables
         # r12 = temporary for the old stack pointer
 
-        ############### Save State ###############
-        # Make space for all register state we will store.
-        leaq -0x38(%rsp), %rsp
+        pushq %rbp
+        movq %rsp, %rbp
+        subq $0x38, %rsp
 
+        ############### Save State ###############
         # Store calee saved general registers.
         movq %r12, 0x00(%rsp)
         movq %r13, 0x08(%rsp)
@@ -42,6 +43,13 @@ __cs_enter_context:
         # Switch to new stack pointer.
         movq %rdi, %rsp
 
+        # Init the new stack (in our case we want the stack trace to 'stick' to where it was created.
+        # This will not necessary be valid all the time (thus returning into it is not ok), but
+        # we only use it for debugging as we explicitly state throwing exceptions beyond the fiber is not ok.
+        # pushq 0x8(%rbp)
+        # pushq 0x0(%rbp)
+        # movq %rsp, %rbp
+
         # Perform actual function call, this will now be on the new stack
         # rdi = first parametor to callback (continuation)
         # rsi = second parameter to callback (arbetary pointer)
@@ -65,14 +73,12 @@ __cs_enter_context:
         ldmxcsr 0x30(%rsp)
         # restore x87 control-word
         fldcw 0x34(%rsp)
-
-        # Free space for restored state
-        leaq 0x38(%rsp), %rsp
         ############ Restore State  ############
 
-        # TODO: Maybe look into a 'cleanup' hook for freeing the stack space here.
-
         # Just return back from the call.
         # This is the end of a fiber, so we have no continuation.
         xor %rax, %rax
+
+        movq %rbp, %rsp
+        popq %rbp
         ret

lib/context_switcher/asm/switch_context_x86_64.s

@@ -11,10 +11,11 @@ __cs_switch_context:
         # Return
         # rax = continuation that returned control back to the caller (null if fallthrough)
 
-        ############### Save State ###############
-        # Make space for all register state we will store.
-        leaq -0x38(%rsp), %rsp
+        pushq %rbp
+        movq %rsp, %rbp
+        subq $0x38, %rsp
 
+        ############### Save State ###############
         # Store calee saved general registers.
         movq %r12, 0x00(%rsp)
         movq %r13, 0x08(%rsp)
@@ -46,11 +47,10 @@ __cs_switch_context:
         ldmxcsr 0x30(%rsp)
         # restore x87 control-word
         fldcw 0x34(%rsp)
-
-        # Free space for restored state
-        leaq 0x38(%rsp), %rsp
         ############ Restore State  ############
 
         # Return the context we came from as a continuation.
         # rax has already the correct value
+        movq %rbp, %rsp
+        popq %rbp
         ret

lib/context_switcher/include/context_switcher/continuation.h

@@ -4,6 +4,9 @@
 
 #include "assembly_bindings.h"
 
+#include <cstdlib>
+#include <cstdio>
+
 namespace context_switcher {
 
 /**
@@ -38,6 +41,10 @@ struct continuation {
   }
 
   assembly_bindings::continuation_t consume() {
+    if (cont_pointer_ == nullptr) {
+      printf("Error!\n");
+    }
+
     auto tmp = cont_pointer_;
     cont_pointer_ = nullptr;
     return tmp;

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

@@ -3,6 +3,7 @@
 #define PLS_INTERNAL_SCHEDULING_TASK_TRADING_DEQUE_H_
 
 #include <atomic>
+#include <utility>
 #include <tuple>
 
 #include "pls/internal/base/error_handling.h"
@@ -18,6 +19,8 @@ namespace pls {
 namespace internal {
 namespace scheduling {
 
+using namespace data_structures;
+
 struct trading_deque_entry {
   std::atomic<task *> traded_task_{nullptr};
   std::atomic<unsigned long> forwarding_stamp_{};
@@ -35,116 +38,171 @@ struct trading_deque_entry {
  * As each task is associated with memory this suffices to exchange memory blocks needed for execution.
  */
 class external_trading_deque {
+
  public:
   external_trading_deque(trading_deque_entry *entries, size_t num_entries) :
       entries_{entries}, num_entries_{num_entries} {};
+  void set_thread_id(unsigned id) {
+    thread_id_ = id;
+  }
+
+  static optional<task *> get_trade_object(task *target_task) {
+    traded_cas_field current_cas = target_task->external_trading_deque_cas_.load();
+    if (current_cas.is_filled_with_object()) {
+      task *result = current_cas.get_trade_object();
+      traded_cas_field empty_cas;
+      if (target_task->external_trading_deque_cas_.compare_exchange_strong(current_cas, empty_cas)) {
+        return optional<task *>{result};
+      }
+    }
+
+    return optional<task *>{};
+  }
 
   /**
    * Pushes a task on the bottom of the deque.
    * The task itself wil be filled with the unique, synchronizing cas word.
    *
    * @param published_task The task to publish on the bottom of the deque.
-   * @return The content of the cas word, can be later used to check if it changed.
    */
-  traded_cas_field push_bot(task *published_task) {
+  void push_bot(task *published_task) {
     auto expected_stamp = bot_internal_.stamp;
     auto &current_entry = entries_[bot_internal_.value];
 
-    // Store stealing information in the task and deque.
-    // Relaxed is fine for this, as adding elements is synced over the bot pointer.
-    current_entry.forwarding_stamp_.store(expected_stamp, std::memory_order_relaxed);
+    // Field that all threads synchronize on.
+    // This happens not in the deque itself, but in the published task.
+    traded_cas_field sync_cas_field;
+    sync_cas_field.fill_with_stamp(expected_stamp, thread_id_);
+    published_task->external_trading_deque_cas_.store(sync_cas_field);
 
-    traded_cas_field new_cas_field;
-    new_cas_field.fill_with_stamp(expected_stamp, deque_id_);
-    published_task->traded_field_.store(new_cas_field, std::memory_order_relaxed);
-    current_entry.traded_task_.store(published_task, std::memory_order_relaxed);
+    // Publish the prepared task in the deque.
+    current_entry.forwarding_stamp_.store(expected_stamp);
+    current_entry.traded_task_.store(published_task);
 
     // Advance the bot pointer. Linearization point for making the task public.
     bot_internal_.stamp++;
     bot_internal_.value++;
-    bot_.store(bot_internal_.value, std::memory_order_release);
+    bot_.store(bot_internal_.value);
+  }
+
+  void reset_bot_and_top() {
+    bot_internal_.value = 0;
+    bot_internal_.stamp++;
 
-    return new_cas_field;
+    bot_.store(0);
+    top_.store({bot_internal_.stamp, 0});
   }
 
-  void popped_bot() {
+  void decrease_bot() {
     bot_internal_.value--;
+    bot_.store(bot_internal_.value);
+  }
 
-    bot_.store(bot_internal_.value, std::memory_order_relaxed);
+  /**
+   * Tries to pop the last task on the deque.
+   *
+   * @return optional<task*> holding the popped task if successful.
+   */
+  optional<task *> pop_bot() {
     if (bot_internal_.value == 0) {
-      bot_internal_.stamp++;
-      top_.store({bot_internal_.stamp, 0}, std::memory_order_release);
+      reset_bot_and_top();
+      return optional<task *>{};
     }
-  }
+    decrease_bot();
 
-  void empty_deque() {
-    bot_internal_.value = 0;
-    bot_internal_.stamp++;
+    auto &current_entry = entries_[bot_internal_.value];
+    auto *popped_task = current_entry.traded_task_.load();
+    auto expected_stamp = current_entry.forwarding_stamp_.load();
 
-    // TODO: We might be able to relax memory orderings...
-    bot_.store(bot_internal_.value);
-    top_.store(bot_internal_);
+    // We know what value must be in the cas field if no other thread stole it.
+    traded_cas_field expected_sync_cas_field;
+    expected_sync_cas_field.fill_with_stamp(expected_stamp, thread_id_);
+    traded_cas_field empty_cas_field;
+
+    if (popped_task->external_trading_deque_cas_.compare_exchange_strong(expected_sync_cas_field, empty_cas_field)) {
+      return optional<task *>{popped_task};
+    } else {
+      reset_bot_and_top();
+      return optional<task *>{};
+    }
   }
 
-  std::tuple<data_structures::optional<task *>, data_structures::stamped_integer> peek_top() {
+  struct peek_result {
+    peek_result(optional<task *> top_task, stamped_integer top_pointer) : top_task_{std::move(top_task)},
+                                                                           top_pointer_{top_pointer} {};
+    optional<task *> top_task_;
+    stamped_integer top_pointer_;
+  };
+
+  /**
+   * Peek at the current task on top of the deque.
+   * This is required, as we need to look at the task to figure out what we trade in for it.
+   * (Note: we could go without this by doing some tricks with top/bot pointers, but this
+   * is simpler and also more flexible if the traded objects are not as trivial as currently).
+   *
+   * @return a peek result containing the optional top task (if present) and the current head pointer.
+   */
+  peek_result peek_top() {
     auto local_top = top_.load();
     auto local_bot = bot_.load();
 
-    if (local_top.value >= local_bot) {
-      return std::make_tuple(data_structures::optional<task *>{}, local_top);
+    if (local_top.value < local_bot) {
+      return peek_result{optional<task *>{entries_[local_top.value].traded_task_}, local_top};
     } else {
-      return std::make_tuple(data_structures::optional<task *>{entries_[local_top.value].traded_task_}, local_top);
+      return peek_result{optional<task *>{}, local_top};
     }
   }
 
-  data_structures::optional<task *> pop_top(task *trade_offer, data_structures::stamped_integer local_top) {
+  optional<task *> pop_top(task *offered_task, stamped_integer expected_top) {
     auto local_bot = bot_.load();
-    if (local_top.value >= local_bot) {
+    if (expected_top.value >= local_bot) {
       return data_structures::optional<task *>{};
     }
 
-    unsigned long expected_top_stamp = local_top.stamp;
-    auto &target_entry = entries_[local_top.value];
+    auto &target_entry = entries_[expected_top.value];
 
     // Read our potential result
-    task *result = target_entry.traded_task_.load(std::memory_order_relaxed);
-    unsigned long forwarding_stamp = target_entry.forwarding_stamp_.load(std::memory_order_relaxed);
+    task *result = target_entry.traded_task_.load();
+    unsigned long forwarding_stamp = target_entry.forwarding_stamp_.load();
+
+    // Try to get it by CAS with the expected field entry, giving up our offered_task for it
+    traded_cas_field expected_sync_cas_field;
+    expected_sync_cas_field.fill_with_stamp(expected_top.stamp, thread_id_);
 
-    // Try to get it by CAS with the expected field entry, giving up our offered_object for it
-    traded_cas_field expected_field;
-    expected_field.fill_with_stamp(expected_top_stamp, deque_id_);
     traded_cas_field offered_field;
-    offered_field.fill_with_trade_object(trade_offer);
+    offered_field.fill_with_trade_object(offered_task);
 
-    if (result->traded_field_.compare_exchange_strong(expected_field, offered_field, std::memory_order_acq_rel)) {
+    if (result->external_trading_deque_cas_.compare_exchange_strong(expected_sync_cas_field, offered_field)) {
       // We got it, for sure move the top pointer forward.
-      top_.compare_exchange_strong(local_top, {local_top.stamp + 1, local_top.value + 1});
+      top_.compare_exchange_strong(expected_top, {expected_top.stamp + 1, expected_top.value + 1});
       // Return the stolen task
       return data_structures::optional<task *>{result};
     } else {
       // We did not get it...help forwarding the top pointer anyway.
-      if (expected_top_stamp == forwarding_stamp) {
+      if (expected_top.stamp == forwarding_stamp) {
         // ...move the pointer forward if someone else put a valid trade object in there.
-        top_.compare_exchange_strong(local_top, {local_top.stamp + 1, local_top.value + 1});
+        top_.compare_exchange_strong(expected_top, {expected_top.stamp + 1, expected_top.value + 1});
       } else {
         // ...we failed because the top tag lags behind...try to fix it.
         // This means only updating the tag, as this location can still hold data we need.
-        top_.compare_exchange_strong(local_top, {forwarding_stamp, local_top.value});
+        top_.compare_exchange_strong(expected_top, {forwarding_stamp, expected_top.value});
       }
       return data_structures::optional<task *>{};
     }
   }
 
  private:
-  trading_deque_entry *entries_;
-  size_t num_entries_;
+  // info on this deque
+  trading_deque_entry *const entries_;
+  const size_t num_entries_;
+  unsigned thread_id_;
 
-  unsigned deque_id_;
+  // fields for stealing/interacting
+  stamped_integer bot_internal_{0, 0};
 
-  alignas(base::system_details::CACHE_LINE_SIZE) std::atomic<data_structures::stamped_integer> top_{{0, 0}};
+  alignas(base::system_details::CACHE_LINE_SIZE) std::atomic<stamped_integer> top_{{0, 0}};
   alignas(base::system_details::CACHE_LINE_SIZE) std::atomic<size_t> bot_{0};
 
-  data_structures::stamped_integer bot_internal_{0, 0};
 };
 
 template<size_t SIZE>

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

@@ -55,7 +55,7 @@ struct alignas(base::system_details::CACHE_LINE_SIZE) task {
   context_switcher::continuation continuation_;
 
   // Work-Stealing
-  std::atomic<traded_cas_field> traded_field_{};
+  std::atomic<traded_cas_field> external_trading_deque_cas_{};
   task *resource_stack_next_{};
   std::atomic<data_structures::stamped_integer> resource_stack_root_{{0, 0}};
   bool clean_;

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

@@ -38,6 +38,7 @@ class task_manager {
     for (size_t i = 0; i < num_tasks_; i++) {
       this_thread_tasks_[i].thread_id_ = id;
     }
+    deque_.set_thread_id(id);
   }
 
   task &get_active_task() {

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

@@ -27,30 +27,33 @@ void task_manager::spawn_child(F &&lambda) {
         last_task->continuation_ = std::move(cont);
         spawning_task_manager->active_task_ = this_task;
 
-        traded_cas_field expected_cas_value = spawning_task_manager->deque_.push_bot(last_task);
-        traded_cas_field empty_cas;
-
+        spawning_task_manager->deque_.push_bot(last_task);
         lambda();
         auto *syncing_task_manager = &thread_state::get().get_task_manager();
 
-        if (last_task->traded_field_.compare_exchange_strong(expected_cas_value, empty_cas)) {
+        auto pop_result = syncing_task_manager->deque_.pop_bot();
+        if (pop_result) {
           // Fast path, simply continue execution where we left of before spawn.
-          // This requires no coordination with the resource stack.
+          PLS_ASSERT(*pop_result == last_task,
+                     "Fast path, nothing can have changed until here.");
+          PLS_ASSERT(spawning_task_manager == syncing_task_manager,
+                     "Fast path, nothing can have changed here.");
+          PLS_ASSERT(last_task->continuation_.valid(),
+                     "Fast path, no one can have continued working on the last task.");
+
           syncing_task_manager->active_task_ = last_task;
-          syncing_task_manager->deque_.popped_bot();
           return std::move(last_task->continuation_);
         } else {
           // Slow path, the continuation was stolen.
-          // First empty our own deque (everything below must have been stolen already).
-          syncing_task_manager->deque_.empty_deque();
-
           context_switcher::continuation result_cont;
           if (syncing_task_manager->try_clean_return(result_cont)) {
             // We return back to the main scheduling loop
-            return result_cont;
+            PLS_ASSERT(result_cont.valid(), "Must only return valid continuations...");
+            return std::move(result_cont);
           } else {
             // We finish up the last task and are the sole owner again
-            return result_cont;
+            PLS_ASSERT(result_cont.valid(), "Must only return valid continuations...");
+            return std::move(result_cont);
           }
         }
       });

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

@@ -45,17 +45,17 @@ struct traded_cas_field {
 
  public:
   void fill_with_stamp(unsigned long stamp, unsigned long deque_id) {
-    cas_integer_ = (((stamp << STAMP_SHIFT) & STAMP_BITS) | ((stamp << ID_SHIFT) & ID_BITS) | STAMP_TAG);
+    cas_integer_ = (((stamp << STAMP_SHIFT) & STAMP_BITS) | ((deque_id << ID_SHIFT) & ID_BITS) | STAMP_TAG);
   }
   unsigned long get_stamp() {
-    PLS_ASSERT(is_filled_with_tag(), "Must only read out the tag when the traded field contains one.");
+    PLS_ASSERT(is_filled_with_stamp(), "Must only read out the tag when the traded field contains one.");
     return (((unsigned long) cas_integer_) & STAMP_BITS) >> STAMP_SHIFT;
   }
   unsigned long get_deque_id() {
-    PLS_ASSERT(is_filled_with_tag(), "Must only read out the tag when the traded field contains one.");
+    PLS_ASSERT(is_filled_with_stamp(), "Must only read out the tag when the traded field contains one.");
     return (((unsigned long) cas_integer_) & ID_BITS) >> ID_SHIFT;
   }
-  bool is_filled_with_tag() {
+  bool is_filled_with_stamp() {
     return (((unsigned long) cas_integer_) & TAG_BITS) == STAMP_TAG;
   }
 

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

@@ -90,17 +90,16 @@ void scheduler::work_thread_work_section() {
 
         // Move the traded in resource of this active task over to the stack of resources.
         auto *stolen_task = &my_task_manager.get_active_task();
-        traded_cas_field stolen_task_cas = stolen_task->traded_field_.load();
-
+        traded_cas_field stolen_task_cas = stolen_task->external_trading_deque_cas_.load();
         if (stolen_task_cas.is_filled_with_object()) {
           // Push the traded in resource on the resource stack to clear the traded_field for later steals/spawns.
           auto *exchanged_task = stolen_task_cas.get_trade_object();
-
           my_task_manager.push_resource_on_task(stolen_task, exchanged_task);
+
           traded_cas_field empty_field;
           traded_cas_field expected_field;
           expected_field.fill_with_trade_object(exchanged_task);
-          if (stolen_task->traded_field_.compare_exchange_strong(expected_field, empty_field)) {
+          if (stolen_task->external_trading_deque_cas_.compare_exchange_strong(expected_field, empty_field)) {
             // All good, nothing more to do
           } else {
             // The last other active thread took it as its spare resource...

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

@@ -36,8 +36,8 @@ bool task_manager::steal_task(task_manager &stealing_task_manager) {
   PLS_ASSERT(stealing_task_manager.active_task_->depth_ == 0, "Must only steal with clean task chain.");
 
   auto peek = deque_.peek_top();
-  auto optional_target_task = std::get<0>(peek);
-  auto target_top = std::get<1>(peek);
+  auto optional_target_task = peek.top_task_;
+  auto target_top = peek.top_pointer_;
 
   if (optional_target_task) {
     PLS_ASSERT(stealing_task_manager.check_task_chain(), "We are stealing, must not have a bad chain here!");
@@ -56,7 +56,10 @@ bool task_manager::steal_task(task_manager &stealing_task_manager) {
 
     auto optional_result_task = deque_.pop_top(traded_task, target_top);
     if (optional_result_task) {
-      PLS_ASSERT(*optional_result_task == target_task, "We must only steal the task that we peeked at!");
+      PLS_ASSERT(target_task->thread_id_ != traded_task->thread_id_,
+                 "It is impossible to steal an task we already own!");
+      PLS_ASSERT(*optional_result_task == target_task,
+                 "We must only steal the task that we peeked at!");
       // the steal was a success, link the chain so we own the stolen part
       target_task->next_ = next_own_task;
       next_own_task->prev_ = target_task;
@@ -164,14 +167,11 @@ bool task_manager::try_clean_return(context_switcher::continuation &result_cont)
   task *clean_chain = pop_resource_from_task(last_task);
   if (clean_chain == nullptr) {
     // double-check if we are really last one or we only have unlucky timing
-    auto cas_field = last_task->traded_field_.load();
-    if (cas_field.is_filled_with_object()) {
-      traded_cas_field empty_target;
-      if (last_task->traded_field_.compare_exchange_strong(cas_field, empty_target)) {
-        clean_chain = cas_field.get_trade_object();
-      } else {
-        clean_chain = pop_resource_from_task(last_task);
-      }
+    auto optional_cas_task = external_trading_deque::get_trade_object(last_task);
+    if (optional_cas_task) {
+      clean_chain = *optional_cas_task;
+    } else {
+      clean_chain = pop_resource_from_task(last_task);
     }
   }
 

test/scheduling_tests.cpp

 #include <catch.hpp>
 
-#include <atomic>
-#include <thread>
-#include <mutex>
+#include <vector>
 
-#include "pls/internal/scheduling/scheduler.h"
-#include "pls/internal/scheduling/cont.h"
-#include "pls/internal/scheduling/cont_manager.h"
-#include "pls/internal/scheduling/scheduler_memory.h"
-#include "pls/internal/scheduling/parallel_result.h"
+#include "pls/internal/scheduling/traded_cas_field.h"
+#include "pls/internal/scheduling/task.h"
+#include "pls/internal/scheduling/external_trading_deque.h"
 
 using namespace pls::internal::scheduling;
 
-// TODO: Introduce actual tests once multiple threads work...
-TEST_CASE("continuation stealing", "[internal/scheduling/cont_manager.h]") {
-  const int NUM_THREADS = 2;
-  const int NUM_TASKS = 8;
-  const int MAX_TASK_STACK_SIZE = 8;
-  const int NUM_CONTS = 8;
-  const int MAX_CONT_SIZE = 256;
-
-  static_scheduler_memory<NUM_THREADS,
-                          NUM_TASKS,
-                          MAX_TASK_STACK_SIZE,
-                          NUM_CONTS,
-                          MAX_CONT_SIZE> static_scheduler_memory;
-
-  scheduler scheduler{static_scheduler_memory, NUM_THREADS};
-
-  // Coordinate progress to match OUR order
-  std::atomic<int> progress{0};
-
-  // Order:
-  // 0) work on first task on main thread
-  // 1) second thread stole right task
-
-  scheduler.perform_work([&]() {
-    return scheduler::par([&]() {
-      while (progress.load() != 1);
-      return parallel_result<int>{0};
-    }, [&]() {
-      progress.store(1);
-      return parallel_result<int>{0};
-    }).then([&](int, int) {
-
-      return parallel_result<int>{0};
-    });
-  });
+TEST_CASE("traded cas field bitmaps correctly", "[internal/scheduling/traded_cas_field.h]") {
+  traded_cas_field empty_field;
+  REQUIRE(empty_field.is_empty());
+  REQUIRE(!empty_field.is_filled_with_stamp());
+  REQUIRE(!empty_field.is_filled_with_object());
+
+  const int stamp = 42;
+  const int ID = 10;
+  traded_cas_field tag_field;
+  tag_field.fill_with_stamp(stamp, ID);
+  REQUIRE(tag_field.is_filled_with_stamp());
+  REQUIRE(!tag_field.is_empty());
+  REQUIRE(!tag_field.is_filled_with_object());
+  REQUIRE(tag_field.get_stamp() == stamp);
+  REQUIRE(tag_field.get_deque_id() == ID);
+
+  alignas(64) task obj;
+  traded_cas_field obj_field;
+  obj_field.fill_with_trade_object(&obj);
+  REQUIRE(obj_field.is_filled_with_object());
+  REQUIRE(!obj_field.is_empty());
+  REQUIRE(!obj_field.is_filled_with_stamp());
+}
+
+TEST_CASE("external trading deque", "[internal/scheduling/external_trading_deque]") {
+  static_external_trading_deque<16> static_external_trading_deque_1;
+  external_trading_deque &deque_1 = static_external_trading_deque_1.get_deque();
+  deque_1.set_thread_id(1);
+
+  static_external_trading_deque<16> static_external_trading_deque_2;
+  external_trading_deque &deque_2 = static_external_trading_deque_2.get_deque();
+  deque_2.set_thread_id(2);
+
+  std::vector<task> tasks(16);
+
+  SECTION("basic operations") {
+    // Must start empty
+    REQUIRE(!deque_1.pop_bot());
+    REQUIRE(!deque_2.pop_bot());
+
+    // Local push/pop
+    deque_1.push_bot(&tasks[0]);
+    REQUIRE(*deque_1.pop_bot() == &tasks[0]);
+    REQUIRE(!deque_1.pop_bot());
+
+    // Local push, external pop
+    deque_1.push_bot(&tasks[0]);
+    auto peek = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_top(&tasks[1], peek.top_pointer_) == &tasks[0]);
+    REQUIRE(*external_trading_deque::get_trade_object(&tasks[0]) == &tasks[1]);
+    REQUIRE(!deque_1.pop_top(&tasks[1], peek.top_pointer_));
+    REQUIRE(!deque_1.pop_bot());
+
+    // Keeps push/pop order
+    deque_1.push_bot(&tasks[0]);
+    deque_1.push_bot(&tasks[1]);
+    REQUIRE(*deque_1.pop_bot() == &tasks[1]);
+    REQUIRE(*deque_1.pop_bot() == &tasks[0]);
+    REQUIRE(!deque_1.pop_bot());
+
+    deque_1.push_bot(&tasks[0]);
+    deque_1.push_bot(&tasks[1]);
+    auto peek1 = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_top(&tasks[2], peek1.top_pointer_) == &tasks[0]);
+    auto peek2 = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_top(&tasks[3], peek2.top_pointer_) == &tasks[1]);
+  }
+
+  SECTION("Interwined execution #1") {
+    // Two top poppers
+    deque_1.push_bot(&tasks[0]);
+    auto peek1 = deque_1.peek_top();
+    auto peek2 = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_top(&tasks[1], peek1.top_pointer_) == &tasks[0]);
+    REQUIRE(!deque_1.pop_top(&tasks[2], peek2.top_pointer_));
+  }
+
+  SECTION("Interwined execution #2") {
+    // Top and bottom access
+    deque_1.push_bot(&tasks[0]);
+    auto peek1 = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_bot() == &tasks[0]);
+    REQUIRE(!deque_1.pop_top(&tasks[2], peek1.top_pointer_));
+  }
 }