Finish pulling out deque/resource stacks from scheduler logic.

lib/pls/CMakeLists.txt

@@ -39,7 +39,7 @@ add_library(pls STATIC
         include/pls/internal/scheduling/lock_free/task.h
         include/pls/internal/scheduling/lock_free/task_manager.h src/internal/scheduling/lock_free/task_manager.cpp
         include/pls/internal/scheduling/lock_free/external_trading_deque.h src/internal/scheduling/lock_free/external_trading_deque.cpp
-        include/pls/internal/scheduling/lock_free/traded_cas_field.h)
+        include/pls/internal/scheduling/lock_free/traded_cas_field.h src/internal/scheduling/lock_free/task.cpp)
 
 # Dependencies for pls
 target_link_libraries(pls Threads::Threads)

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

@@ -8,12 +8,24 @@
 
 namespace pls::internal::scheduling::lock_free {
 
+/**
+ * Lock free task variant.
+ * Needs extra fields to manage the trading and resources.
+ * RELIES on the fact that tasks have a unique depth and thread id,
+ * allowing to refer to a task solely by this property!
+ */
 struct task : public base_task {
   task(char *stack_memory, size_t stack_size, unsigned depth, unsigned thread_id) :
       base_task(stack_memory, stack_size, depth, thread_id) {}
 
   // Additional info for lock-free stealing and resource trading.
   std::atomic<traded_cas_field> external_trading_deque_cas_{};
+
+  void push_task_chain(task *spare_task_chain);
+  task *pop_task_chain();
+  void reset_task_chain();
+
+ private:
   std::atomic<base_task *> resource_stack_next_{};
   std::atomic<data_structures::stamped_integer> resource_stack_root_{{0, 0}};
 };

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

@@ -5,6 +5,7 @@
 #include <memory>
 #include <utility>
 #include <array>
+#include <tuple>
 
 #include "pls/internal/base/stack_allocator.h"
 
@@ -21,7 +22,8 @@ namespace pls::internal::scheduling::lock_free {
  * Handles management of tasks in the system. Each thread has a local task manager,
  * responsible for allocating, freeing and publishing tasks for stealing.
  *
- * All interaction for spawning, stealing and task trading are managed through this class.
+ * The task manager handles steal/sync details, the scheduler handles all other aspects.
+ * By doing this the task manager can be exchanged for a different implementation for testing purposes.
  */
 class task_manager {
   using stack_allocator = pls::internal::base::stack_allocator;
@@ -40,15 +42,11 @@ class task_manager {
   base_task *pop_local_task();
 
   // Stealing work, automatically trades in another task
-  base_task *steal_task(thread_state &stealing_state);
+  std::tuple<base_task *, base_task *> steal_task(thread_state &stealing_state);
 
   // Sync/memory management
   base_task *pop_clean_task_chain(base_task *task);
  private:
-  // Internal helpers for resource stack on tasks
-  void push_resource_on_task(task *target_task, task *spare_task_chain);
-  task *pop_resource_from_task(task *target_task);
-
   std::shared_ptr<stack_allocator> stack_allocator_;
   std::vector<std::unique_ptr<task>> tasks_;
 

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

 #include "pls/internal/scheduling/base_task.h"
 
-namespace pls {
-namespace internal {
-namespace scheduling {
-
-}
-}
+namespace pls::internal::scheduling {
 }

lib/pls/src/internal/scheduling/lock_free/task.cpp

+#include "pls/internal/scheduling/lock_free/task.h"
+#include "pls/internal/scheduling/scheduler.h"
+
+namespace pls::internal::scheduling::lock_free {
+
+// TODO: this 'global' lookup hardly bound to the full scheduler to be setup could be reworked for better testing.
+static task *find_task(unsigned id, unsigned depth) {
+  return thread_state::get().get_scheduler().thread_state_for(id).get_task_manager().get_task(depth);
+}
+
+void task::push_task_chain(task *spare_task_chain) {
+  PLS_ASSERT(this->thread_id_ != spare_task_chain->thread_id_,
+             "Makes no sense to push task onto itself, as it is not clean by definition.");
+  PLS_ASSERT(this->depth_ == spare_task_chain->depth_,
+             "Must only push tasks with correct depth.");
+
+  data_structures::stamped_integer current_root;
+  data_structures::stamped_integer target_root;
+  do {
+    current_root = this->resource_stack_root_.load();
+    target_root.stamp = current_root.stamp + 1;
+    target_root.value = spare_task_chain->thread_id_ + 1;
+
+    if (current_root.value == 0) {
+      // Empty, simply push in with no successor
+      spare_task_chain->resource_stack_next_.store(nullptr);
+    } else {
+      // Already an entry. Find it's corresponding task and set it as our successor.
+      auto *current_root_task = find_task(current_root.value - 1, this->depth_);
+      spare_task_chain->resource_stack_next_.store(current_root_task);
+    }
+
+  } while (!this->resource_stack_root_.compare_exchange_strong(current_root, target_root));
+}
+
+task *task::pop_task_chain() {
+  data_structures::stamped_integer current_root;
+  data_structures::stamped_integer target_root;
+  task *output_task;
+  do {
+    current_root = this->resource_stack_root_.load();
+    if (current_root.value == 0) {
+      // Empty...
+      return nullptr;
+    } else {
+      // Found something, try to pop it
+      auto *current_root_task = find_task(current_root.value - 1, this->depth_);
+      auto *next_stack_task = current_root_task->resource_stack_next_.load();
+
+      target_root.stamp = current_root.stamp + 1;
+      target_root.value = next_stack_task != nullptr ? next_stack_task->thread_id_ + 1 : 0;
+
+      output_task = current_root_task;
+    }
+  } while (!this->resource_stack_root_.compare_exchange_strong(current_root, target_root));
+
+  PLS_ASSERT(scheduler::check_task_chain_backward(*output_task), "Must only pop proper task chains.");
+  output_task->resource_stack_next_.store(nullptr);
+  return output_task;
+}
+
+void task::reset_task_chain() {
+  auto current_root = this->resource_stack_root_.load();
+  current_root.stamp++;
+  current_root.value = 0;
+  this->resource_stack_root_.store(current_root);
+  this->resource_stack_next_.store(nullptr);
+}
+
+}

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

@@ -14,7 +14,7 @@ task_manager::task_manager(unsigned thread_id,
                                                                                 deque_{thread_id, num_tasks} {
   tasks_.reserve(num_tasks);
 
-  for (size_t i = 0; i < num_tasks - 1; i++) {
+  for (size_t i = 0; i < num_tasks; i++) {
     char *stack_memory = stack_allocator->allocate_stack(stack_size);
     tasks_.emplace_back(std::make_unique<task>(stack_memory, stack_size, i, thread_id));
 
@@ -31,10 +31,6 @@ task_manager::~task_manager() {
   }
 }
 
-static task *find_task(unsigned id, unsigned depth) {
-  return thread_state::get().get_scheduler().thread_state_for(id).get_task_manager().get_task(depth);
-}
-
 void task_manager::push_local_task(base_task *pushed_task) {
   deque_.push_bot(static_cast<task *>(pushed_task));
 }
@@ -48,21 +44,17 @@ base_task *task_manager::pop_local_task() {
   }
 }
 
-base_task *task_manager::steal_task(thread_state &stealing_state) {
+std::tuple<base_task *, base_task *> task_manager::steal_task(thread_state &stealing_state) {
   PLS_ASSERT(stealing_state.get_active_task()->depth_ == 0, "Must only steal with clean task chain.");
   PLS_ASSERT(scheduler::check_task_chain(*stealing_state.get_active_task()), "Must only steal with clean task chain.");
 
   auto peek = deque_.peek_top();
   if (peek.top_task_) {
-    // search for the task we want to trade in
     task *stolen_task = static_cast<task *>(*peek.top_task_);
+    // get a suitable task to trade in
+    // TODO: opt. add debug marker to traded in tasks that we do not accidentally use them.
     task *traded_task = static_cast<task *>(&scheduler::task_chain_at(stolen_task->depth_, stealing_state));
 
-    // keep a reference to the rest of the task chain that we keep
-    base_task *next_own_task = traded_task->next_;
-    // 'unchain' the traded tasks (to help us find bugs)
-    traded_task->next_ = nullptr;
-
     // perform the actual pop operation
     auto pop_result_task = deque_.pop_top(traded_task, peek);
     if (pop_result_task) {
@@ -71,15 +63,8 @@ base_task *task_manager::steal_task(thread_state &stealing_state) {
       PLS_ASSERT(*pop_result_task == stolen_task,
                  "We must only steal the task that we peeked at!");
 
-      // TODO: the re-chaining should not be part of the task manager.
-      //  The manager should only perform the steal + resource push.
-
-      // the steal was a success, link the chain so we own the stolen part
-      stolen_task->next_ = next_own_task;
-      next_own_task->prev_ = stolen_task;
-
       // update the resource stack associated with the stolen task
-      push_resource_on_task(stolen_task, traded_task);
+      stolen_task->push_task_chain(traded_task);
 
       auto optional_exchanged_task = external_trading_deque::get_trade_object(stolen_task);
       if (optional_exchanged_task) {
@@ -89,90 +74,34 @@ base_task *task_manager::steal_task(thread_state &stealing_state) {
       } else {
         // The last other active thread took it as its spare resource...
         // ...remove our traded object from the stack again (it must be empty now and no one must access it anymore).
-        auto current_root = stolen_task->resource_stack_root_.load();
-        current_root.stamp++;
-        current_root.value = 0;
-        stolen_task->resource_stack_root_.store(current_root);
+        stolen_task->reset_task_chain();
       }
 
-      return stolen_task;
+      return std::pair{stolen_task, traded_task};
     } else {
-      // the steal failed, reset our chain to its old, clean state (re-link what we have broken)
-      traded_task->next_ = next_own_task;
-
-      return nullptr;
+      return std::pair{nullptr, nullptr};
     }
   } else {
-    return nullptr;
+    return std::pair{nullptr, nullptr};
   }
 }
 
 base_task *task_manager::pop_clean_task_chain(base_task *base_task) {
   task *popped_task = static_cast<task *>(base_task);
   // Try to get a clean resource chain to go back to the main stealing loop
-  task *clean_chain = pop_resource_from_task(popped_task);
+  task *clean_chain = popped_task->pop_task_chain();
   if (clean_chain == nullptr) {
     // double-check if we are really last one or we only have unlucky timing
     auto optional_cas_task = external_trading_deque::get_trade_object(popped_task);
     if (optional_cas_task) {
       clean_chain = *optional_cas_task;
     } else {
-      clean_chain = pop_resource_from_task(popped_task);
+      clean_chain = popped_task->pop_task_chain();
     }
   }
 
   return clean_chain;
 }
 
-void task_manager::push_resource_on_task(task *target_task, task *spare_task_chain) {
-  PLS_ASSERT(target_task->thread_id_ != spare_task_chain->thread_id_,
-             "Makes no sense to push task onto itself, as it is not clean by definition.");
-  PLS_ASSERT(target_task->depth_ == spare_task_chain->depth_,
-             "Must only push tasks with correct depth.");
-
-  data_structures::stamped_integer current_root;
-  data_structures::stamped_integer target_root;
-  do {
-    current_root = target_task->resource_stack_root_.load();
-    target_root.stamp = current_root.stamp + 1;
-    target_root.value = spare_task_chain->thread_id_ + 1;
-
-    if (current_root.value == 0) {
-      // Empty, simply push in with no successor
-      spare_task_chain->resource_stack_next_.store(nullptr);
-    } else {
-      // Already an entry. Find it's corresponding task and set it as our successor.
-      auto *current_root_task = find_task(current_root.value - 1, target_task->depth_);
-      spare_task_chain->resource_stack_next_.store(current_root_task);
-    }
-
-  } while (!target_task->resource_stack_root_.compare_exchange_strong(current_root, target_root));
-}
-
-task *task_manager::pop_resource_from_task(task *target_task) {
-  data_structures::stamped_integer current_root;
-  data_structures::stamped_integer target_root;
-  task *output_task;
-  do {
-    current_root = target_task->resource_stack_root_.load();
-    if (current_root.value == 0) {
-      // Empty...
-      return nullptr;
-    } else {
-      // Found something, try to pop it
-      auto *current_root_task = find_task(current_root.value - 1, target_task->depth_);
-      auto *next_stack_task = current_root_task->resource_stack_next_.load();
-
-      target_root.stamp = current_root.stamp + 1;
-      target_root.value = next_stack_task != nullptr ? next_stack_task->thread_id_ + 1 : 0;
-
-      output_task = current_root_task;
-    }
-  } while (!target_task->resource_stack_root_.compare_exchange_strong(current_root, target_root));
-
-  PLS_ASSERT(scheduler::check_task_chain_backward(*output_task), "Must only pop proper task chains.");
-  output_task->resource_stack_next_.store(nullptr);
-  return output_task;
-}
 
 }

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

@@ -56,13 +56,14 @@ void scheduler::work_thread_work_section() {
     } while (target == my_state.get_thread_id());
 
     thread_state &target_state = my_state.get_scheduler().thread_state_for(target);
-    base_task *stolen_task = target_state.get_task_manager().steal_task(my_state);
+    auto[stolen_task, traded_task] = target_state.get_task_manager().steal_task(my_state);
     if (stolen_task) {
+      // Keep task chain consistent. We want to appear as if we are working an a branch upwards of the stolen task.
+      base_task *next_own_task = traded_task->next_;
+      stolen_task->next_ = next_own_task;
+      next_own_task->prev_ = stolen_task;
       my_state.set_active_task(stolen_task);
-      // TODO: Figure out how to model 'steal' interaction .
-      //  The scheduler should decide on 'what to steal' and on how 'to manage the chains'.
-      //  The task_manager should perform the act of actually performing the steal/trade.
-      //  Maybe also give the chain management to the task_manager and associate resources with the traded tasks.
+
       PLS_ASSERT(check_task_chain_forward(*my_state.get_active_task()),
                  "We are sole owner of this chain, it has to be valid!");
 

test/CMakeLists.txt

@@ -4,5 +4,5 @@ add_executable(tests
         base_tests.cpp
         scheduling_tests.cpp
         patterns_test.cpp
-        test_helpers.h)
+        test_helpers.h scheduling_lock_free_tests.cpp)
 target_link_libraries(tests catch2 pls)

test/scheduling_lock_free_tests.cpp

+#include <catch.hpp>
+
+#include <atomic>
+
+#include "pls/pls.h"
+#include "pls/internal/scheduling/task_manager.h"
+#include "pls/internal/scheduling/thread_state.h"
+
+#if PLS_DEQUE_VARIANT == PLS_DEQUE_LOCK_FREE
+#include "pls/internal/scheduling/lock_free/traded_cas_field.h"
+#include "pls/internal/scheduling/lock_free/external_trading_deque.h"
+
+using namespace pls::internal::scheduling::lock_free;
+
+TEST_CASE("traded cas field bitmaps correctly", "[internal/scheduling/lock_free/traded_cas_field]") {
+  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{nullptr, 0, 0, 0};
+  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("task resource stack", "[internal/scheduling/lock_free/task]") {
+  // simulate scheduler with four threads and depth 1. We are thread 0.
+  pls::scheduler scheduler{4, 1, 4096, false};
+  pls::internal::scheduling::thread_state::set(&scheduler.thread_state_for(0));
+
+  task *tasks[] = {scheduler.task_manager_for(0).get_task(0),
+                   scheduler.task_manager_for(1).get_task(0),
+                   scheduler.task_manager_for(2).get_task(0),
+                   scheduler.task_manager_for(3).get_task(0)};
+
+  SECTION("simple push/pop") {
+    tasks[0]->push_task_chain(tasks[1]);
+
+    REQUIRE(tasks[0]->pop_task_chain() == tasks[1]);
+    REQUIRE(tasks[0]->pop_task_chain() == nullptr);
+  }
+
+  SECTION("multiple pushes") {
+    tasks[0]->push_task_chain(tasks[1]);
+    tasks[0]->push_task_chain(tasks[2]);
+    tasks[0]->push_task_chain(tasks[3]);
+
+    REQUIRE(tasks[0]->pop_task_chain() == tasks[3]);
+    REQUIRE(tasks[0]->pop_task_chain() == tasks[2]);
+    REQUIRE(tasks[0]->pop_task_chain() == tasks[1]);
+    REQUIRE(tasks[0]->pop_task_chain() == nullptr);
+  }
+}
+
+TEST_CASE("external trading deque", "[internal/scheduling/lock_free/external_trading_deque]") {
+  external_trading_deque deque_1{1, 16};
+  external_trading_deque deque_2{2, 16};
+
+  task tasks[4] = {{nullptr, 0, 0, 0},
+                   {nullptr, 0, 1, 0},
+                   {nullptr, 0, 2, 0},
+                   {nullptr, 0, 3, 0}};
+
+  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) == &tasks[0]);
+    REQUIRE(*external_trading_deque::get_trade_object(&tasks[0]) == &tasks[1]);
+    REQUIRE(!deque_1.pop_top(&tasks[1], peek));
+    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) == &tasks[0]);
+    auto peek2 = deque_1.peek_top();
+    REQUIRE(*deque_1.pop_top(&tasks[3], peek2) == &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) == &tasks[0]);
+    REQUIRE(!deque_1.pop_top(&tasks[2], peek2));
+  }
+
+  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));
+  }
+}
+#endif // PLS_DEQUE_VARIANT == PLS_DEQUE_LOCK_FREE

test/scheduling_tests.cpp

 #include <catch.hpp>
-
 #include <atomic>
 
-#include "pls/internal/scheduling/lock_free/traded_cas_field.h"
-#include "pls/internal/scheduling/lock_free/external_trading_deque.h"
 #include "pls/pls.h"
 
 using namespace pls::internal::scheduling;
-using namespace pls::internal::scheduling::lock_free;
 
 constexpr int MAX_NUM_TASKS = 32;
 constexpr int MAX_STACK_SIZE = 1024 * 8;
 
-TEST_CASE("tasks distributed over workers (do not block)", "[internal/scheduling/scheduler.h]") {
+TEST_CASE("scheduler correctly initializes", "[internal/scheduling/scheduler]") {
+  const unsigned num_tasks = 16;
+  const unsigned num_threads = 4;
+
+  pls::scheduler scheduler{num_threads, num_tasks, 4096, false};
+
+  SECTION("task chains are valid") {
+    for (unsigned i = 0; i < num_threads; i++) {
+      task_manager &manager = scheduler.task_manager_for(i);
+      for (unsigned j = 0; j < num_tasks; j++) {
+        REQUIRE(manager.get_task(j)->depth_ == j);
+        REQUIRE(manager.get_task(j)->thread_id_ == i);
+
+        if (j < num_tasks - 1) {
+          REQUIRE(manager.get_task(j)->next_ == manager.get_task(j + 1));
+        }
+        if (j > 0) {
+          REQUIRE(manager.get_task(j)->prev_ == manager.get_task(j - 1));
+        }
+      }
+    }
+  }
+}
+
+TEST_CASE("tasks distributed over workers (do not block)", "[internal/scheduling/scheduler]") {
   scheduler scheduler{3, MAX_NUM_TASKS, MAX_STACK_SIZE};
 
   std::atomic<int> num_run{0};
@@ -34,87 +54,3 @@ TEST_CASE("tasks distributed over workers (do not block)", "[internal/scheduling
   });
   REQUIRE(num_run == 3);
 }
-
-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{nullptr, 0, 0, 0};
-  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]") {
-  external_trading_deque deque_1{1, 16};
-  external_trading_deque deque_2{2, 16};
-
-  task tasks[4] = {{nullptr, 0, 0, 0},
-                   {nullptr, 0, 1, 0},
-                   {nullptr, 0, 2, 0},
-                   {nullptr, 0, 3, 0}};
-
-  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) == &tasks[0]);
-    REQUIRE(*external_trading_deque::get_trade_object(&tasks[0]) == &tasks[1]);
-    REQUIRE(!deque_1.pop_top(&tasks[1], peek));
-    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) == &tasks[0]);
-    auto peek2 = deque_1.peek_top();
-    REQUIRE(*deque_1.pop_top(&tasks[3], peek2) == &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) == &tasks[0]);
-    REQUIRE(!deque_1.pop_top(&tasks[2], peek2));
-  }
-
-  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));
-  }
-}