Add API for starting top level tasks.

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

@@ -19,7 +19,9 @@ namespace pls {
                 static std::uintptr_t next_alignment(std::uintptr_t size);
                 static char* next_alignment(char* pointer);
             public:
-                explicit aligned_stack(char* memory_region, const std::size_t size):
+                aligned_stack(): memory_start_{nullptr}, memory_end_{nullptr}, head_{nullptr} {};
+
+                aligned_stack(char* memory_region, const std::size_t size):
                     memory_start_{memory_region},
                     memory_end_{memory_region + size},
                     head_{next_alignment(memory_start_)} {}

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

@@ -5,9 +5,11 @@
 #include <array>
 #include <iostream>
 
+#include "pls/internal/base/aligned_stack.h"
 #include "pls/internal/base/thread.h"
 #include "pls/internal/base/barrier.h"
 #include "pls/internal/scheduling/thread_state.h"
+
 #include "root_master_task.h"
 #include "root_worker_task.h"
 
@@ -18,78 +20,87 @@ namespace pls {
             // Could be moved to templating if needed.
             static constexpr int MAX_THREADS = 32;
 
-            class scheduler {
-                static void worker_routine() {
-                    auto my_state = base::this_thread::state<thread_state>();
+            void worker_routine();
+            using scheduler_thread = base::thread<decltype(&worker_routine), thread_state>;
 
-                    while (true) {
-                        my_state->scheduler_->sync_barrier_.wait();
-                        if (my_state->scheduler_->terminated_) {
-                            return;
-                        }
+            class scheduler_memory {
+            public:
+                virtual size_t max_threads() = 0;
+                virtual thread_state* thread_state_for(size_t id) = 0;
+                virtual scheduler_thread* thread_for(size_t id) = 0;
+                virtual base::aligned_stack* task_stack_for(size_t id) = 0;
+            };
 
-                        // The root task must only return when all work is done,
-                        // because of this a simple call is enough to ensure the
-                        // fork-join-section is done (logically joined back into our main thread).
-                        my_state->root_task_->execute();
+            template<size_t MAX_THREADS, size_t TASK_STACK_SIZE>
+            class static_scheduler_memory: public scheduler_memory {
+                std::array<scheduler_thread, MAX_THREADS> threads_;
+                std::array<thread_state, MAX_THREADS> thread_states_;
+                std::array<std::array<char, TASK_STACK_SIZE>, MAX_THREADS> task_stacks_memory_;
+                std::array<base::aligned_stack, MAX_THREADS> task_stacks_;
 
-                        my_state->scheduler_->sync_barrier_.wait();
+            public:
+                static_scheduler_memory() {
+                    for (size_t i = 0; i < MAX_THREADS; i++) {
+                        task_stacks_[i] = base::aligned_stack(reinterpret_cast<char*>(&task_stacks_memory_[i]), TASK_STACK_SIZE);
                     }
                 }
 
+                size_t max_threads() override { return MAX_THREADS; }
+                thread_state* thread_state_for(size_t id) override { return &thread_states_[id]; }
+                scheduler_thread* thread_for(size_t id) override { return &threads_[id]; }
+                base::aligned_stack* task_stack_for(size_t id) override { return &task_stacks_[id]; }
+            };
+
+            class scheduler {
+                friend void worker_routine();
+
                 unsigned int num_threads_;
-                std::array<thread_state, MAX_THREADS> thread_states_;
-                std::array<base::thread<decltype(&worker_routine), thread_state>, MAX_THREADS> threads_;
+                scheduler_memory* memory_;
 
                 base::barrier sync_barrier_;
                 bool terminated_;
             public:
-                explicit scheduler(const unsigned int num_threads):
-                    num_threads_{num_threads},
-                    sync_barrier_{num_threads + 1},
-                    terminated_{false} {
-                    if (num_threads > MAX_THREADS) {
-                        exit(1); // TODO: Exception Handling
-                    }
-
-                    for (unsigned int i = 0; i < num_threads; i++) {
-                        thread_states_[i] = thread_state{this};
-                        threads_[i] = base::start_thread(&worker_routine, &thread_states_[i]);
-                    }
-                }
-
-                ~scheduler() {
-                    terminate();
-                }
+                explicit scheduler(scheduler_memory* memory, unsigned int num_threads);
+                ~scheduler();
 
                 template<typename Function>
                 void perform_work(Function work_section) {
                     root_master_task<Function> master{work_section};
                     root_worker_task<Function> worker{&master};
 
-                    thread_states_[0].root_task_ = &master;
+                    // Push root task on stacks
+                    memory_->thread_state_for(0)->root_task_ = memory_->task_stack_for(0)->push(master);
                     for (unsigned int i = 1; i < num_threads_; i++) {
-                        thread_states_[i].root_task_ = &worker;
+                        memory_->thread_state_for(i)->root_task_ = memory_->task_stack_for(i)->push(worker);
                     }
 
+                    // Perform and wait for work
                     sync_barrier_.wait(); // Trigger threads to wake up
                     sync_barrier_.wait(); // Wait for threads to finish
-                }
 
-                void terminate(bool wait_for_workers=true) {
-                    if (terminated_) {
-                        return;
+                    // Remove root task from stacks
+                    memory_->task_stack_for(0)->pop<typeof(master)>();
+                    for (unsigned int i = 1; i < num_threads_; i++) {
+                        memory_->task_stack_for(i)->pop<typeof(worker)>();
                     }
+                }
 
-                    terminated_ = true;
-                    sync_barrier_.wait();
+                // TODO: See if we should place this differently (only for performance reasons)
+                template<typename Task>
+                void execute_task(Task& task) {
+                    static_assert(std::is_base_of<abstract_task, Task>::value, "Only pass abstract_task subclasses!");
 
-                    if (wait_for_workers) {
-                        for (unsigned int i = 0; i < num_threads_; i++) {
-                            threads_[i].join();
-                        }
-                    }
+                    auto my_state = base::this_thread::state<thread_state>();
+                    auto task_stack = my_state->task_stack_;
+
+                    // TODO: Assert if 'top level' task even have to go somewhere or if
+                    //       we can simply keep the on the call stack.
+                    auto my_task = task_stack->push(task);
+                    my_task.execute();
+                    task_stack->pop<Task>();
                 }
+
+                void terminate(bool wait_for_workers=true);
             };
         }
     }

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

@@ -11,11 +11,15 @@ namespace pls {
             class scheduler;
 
             struct thread_state {
-                thread_state(): scheduler_{nullptr}, root_task_{nullptr} {};
-                explicit thread_state(scheduler* scheduler): scheduler_{scheduler}, root_task_{nullptr} {}
+                thread_state(): scheduler_{nullptr}, root_task_{nullptr}, task_stack_{nullptr} {};
+                explicit thread_state(scheduler* scheduler, base::aligned_stack* task_stack):
+                    scheduler_{scheduler},
+                    root_task_{nullptr},
+                    task_stack_{task_stack} {}
 
                 scheduler* scheduler_;
                 abstract_task* root_task_;
+                base::aligned_stack* task_stack_;
             };
         }
     }

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

@@ -3,7 +3,57 @@
 namespace pls {
     namespace internal {
         namespace scheduling {
+            scheduler::scheduler(scheduler_memory* memory, const unsigned int num_threads):
+                    num_threads_{num_threads},
+                    memory_{memory},
+                    sync_barrier_{num_threads + 1},
+                    terminated_{false} {
+                if (num_threads > MAX_THREADS) {
+                    exit(1); // TODO: Exception Handling
+                }
 
+                for (unsigned int i = 0; i < num_threads; i++) {
+                    *memory_->thread_state_for(i) = thread_state{this, memory_->task_stack_for(i)};
+                    *memory_->thread_for(i) = base::start_thread(&worker_routine, memory_->thread_state_for(i));
+                }
+            }
+
+            scheduler::~scheduler() {
+                terminate();
+            }
+
+            void worker_routine() {
+                auto my_state = base::this_thread::state<thread_state>();
+
+                while (true) {
+                    my_state->scheduler_->sync_barrier_.wait();
+                    if (my_state->scheduler_->terminated_) {
+                        return;
+                    }
+
+                    // The root task must only return when all work is done,
+                    // because of this a simple call is enough to ensure the
+                    // fork-join-section is done (logically joined back into our main thread).
+                    my_state->root_task_->execute();
+
+                    my_state->scheduler_->sync_barrier_.wait();
+                }
+            }
+
+            void scheduler::terminate(bool wait_for_workers) {
+                if (terminated_) {
+                    return;
+                }
+
+                terminated_ = true;
+                sync_barrier_.wait();
+
+                if (wait_for_workers) {
+                    for (unsigned int i = 0; i < num_threads_; i++) {
+                        memory_->thread_for(i)->join();
+                    }
+                }
+            }
         }
     }
 }