Create a RefCounted type and use it for Thread.

This should prevent me from actually creating 2 shared ptrs of
a single kernel object with their separate ref counts.

zion/lib/ref_counted.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "debug/debug.h"
+
+template <typename T>
+class RefCounted {
+ public:
+  RefCounted() {}
+  ~RefCounted() { dbgln("RefCounted object destroyed"); }
+  void Adopt() {
+    if (ref_count_ != -1) {
+      panic("Adopting owned ptr");
+    } else {
+      ref_count_ = 1;
+    }
+  }
+
+  void Acquire() {
+    if (ref_count_ == -1) {
+      panic("Acquiring unowned ptr");
+    }
+    ref_count_++;
+  }
+  bool Release() {
+    if (ref_count_ == -1 || ref_count_ == 0) {
+      panic("Releasing unowned ptr");
+    }
+    return (--ref_count_) == 0;
+  }
+
+ private:
+  // FIXME: This should be an atomic type.
+  uint64_t ref_count_ = -1;
+  // Disallow copy and move.
+  RefCounted(RefCounted&) = delete;
+  RefCounted(RefCounted&&) = delete;
+  RefCounted& operator=(RefCounted&) = delete;
+  RefCounted& operator=(RefCounted&&) = delete;
+};

zion/lib/ref_ptr.h

@@ -0,0 +1,76 @@
+#pragma once
+
+template <typename T>
+class RefPtr;
+
+template <typename T>
+RefPtr<T> AdoptPtr(T* ptr);
+
+template <typename T>
+class RefPtr {
+ public:
+  RefPtr() : ptr_(nullptr) {}
+  RefPtr(decltype(nullptr)) : ptr_(nullptr) {}
+  RefPtr(const RefPtr& other) : ptr_(other.ptr_) {
+    if (ptr_) {
+      ptr_->Acquire();
+    }
+  }
+  RefPtr& operator=(const RefPtr& other) {
+    T* old = ptr_;
+    ptr_ = other.ptr_;
+    if (ptr_) {
+      ptr_->Acquire();
+    }
+    if (old && old->Release()) {
+      delete old;
+    }
+
+    return *this;
+  }
+
+  RefPtr(RefPtr&& other) : ptr_(other.ptr_) { other.ptr_ = nullptr; }
+  RefPtr& operator=(RefPtr&& other) {
+    // Swap
+    T* ptr = ptr_;
+    ptr_ = other.ptr_;
+    other.ptr_ = ptr;
+    return *this;
+  }
+
+  T* get() const { return ptr_; };
+  T& operator*() const { return *ptr_; }
+  T* operator->() const { return ptr_; }
+  operator bool() const { return ptr_ != nullptr; }
+
+  bool operator==(decltype(nullptr)) const { return (ptr_ == nullptr); }
+  bool operator!=(decltype(nullptr)) const { return (ptr_ != nullptr); }
+
+  bool operator==(const RefPtr<T>& other) const { return (ptr_ == other.ptr_); }
+  bool operator!=(const RefPtr<T>& other) const { return (ptr_ != other.ptr_); }
+
+ private:
+  T* ptr_;
+
+  friend RefPtr<T> AdoptPtr<T>(T* ptr);
+  RefPtr(T* ptr) : ptr_(ptr) { ptr->Adopt(); }
+};
+
+template <typename T>
+class MakeRefCountedFriend final {
+ public:
+  template <typename... Args>
+  static RefPtr<T> Make(Args&&... args) {
+    return AdoptPtr(new T(args...));
+  }
+};
+
+template <typename T, typename... Args>
+RefPtr<T> MakeRefCounted(Args&&... args) {
+  return MakeRefCountedFriend<T>::Make(args...);
+}
+
+template <typename T>
+RefPtr<T> AdoptPtr(T* ptr) {
+  return RefPtr(ptr);
+}

zion/scheduler/process.cpp

@@ -26,13 +26,13 @@ Process::Process() : id_(gNextId++), state_(RUNNING) {
                                 ZC_PROC_SPAWN_PROC | ZC_PROC_SPAWN_THREAD));
 }
 
-SharedPtr<Thread> Process::CreateThread() {
-  SharedPtr<Thread> thread{new Thread(*this, next_thread_id_++)};
+RefPtr<Thread> Process::CreateThread() {
+  RefPtr<Thread> thread = MakeRefCounted<Thread>(*this, next_thread_id_++);
   threads_.PushBack(thread);
   return thread;
 }
 
-SharedPtr<Thread> Process::GetThread(uint64_t tid) {
+RefPtr<Thread> Process::GetThread(uint64_t tid) {
   auto iter = threads_.begin();
   while (iter != threads_.end()) {
     if (iter->tid() == tid) {
@@ -67,9 +67,9 @@ SharedPtr<Capability> Process::GetCapability(uint64_t cid) {
   return {};
 }
 
-uint64_t Process::AddCapability(SharedPtr<Thread>& thread) {
+uint64_t Process::AddCapability(RefPtr<Thread>& thread) {
   uint64_t cap_id = next_cap_id_++;
   caps_.PushBack(
-      new Capability(thread.ptr(), Capability::THREAD, cap_id, ZC_WRITE));
+      new Capability(thread.get(), Capability::THREAD, cap_id, ZC_WRITE));
   return cap_id;
 }

zion/scheduler/process.h

@@ -4,6 +4,7 @@
 
 #include "capability/capability.h"
 #include "lib/linked_list.h"
+#include "lib/ref_ptr.h"
 #include "lib/shared_ptr.h"
 #include "memory/virtual_memory.h"
 
@@ -24,11 +25,11 @@ class Process {
   uint64_t id() const { return id_; }
   VirtualMemory& vmm() { return vmm_; }
 
-  SharedPtr<Thread> CreateThread();
-  SharedPtr<Thread> GetThread(uint64_t tid);
+  RefPtr<Thread> CreateThread();
+  RefPtr<Thread> GetThread(uint64_t tid);
 
   SharedPtr<Capability> GetCapability(uint64_t cid);
-  uint64_t AddCapability(SharedPtr<Thread>& t);
+  uint64_t AddCapability(RefPtr<Thread>& t);
   // Checks the state of all child threads and transitions to
   // finished if all have finished.
   void CheckState();
@@ -44,6 +45,6 @@ class Process {
   uint64_t next_thread_id_ = 0;
   uint64_t next_cap_id_ = 0x100;
 
-  LinkedList<SharedPtr<Thread>> threads_;
+  LinkedList<RefPtr<Thread>> threads_;
   LinkedList<SharedPtr<Capability>> caps_;
 };

zion/scheduler/scheduler.cpp

@@ -48,7 +48,7 @@ void Scheduler::Preempt() {
     return;
   }
 
-  SharedPtr<Thread> prev = current_thread_;
+  RefPtr<Thread> prev = current_thread_;
   prev->SetState(Thread::RUNNABLE);
   current_thread_ = runnable_threads_.CycleFront(prev);
 
@@ -62,7 +62,7 @@ void Scheduler::Yield() {
   }
   asm volatile("cli");
 
-  SharedPtr<Thread> prev = current_thread_;
+  RefPtr<Thread> prev = current_thread_;
   if (prev == sleep_thread_) {
     if (runnable_threads_.size() == 0) {
       panic("Sleep thread yielded without next.");

zion/scheduler/scheduler.h

@@ -15,7 +15,7 @@ class Scheduler {
   Process& CurrentProcess() { return current_thread_->process(); }
   Thread& CurrentThread() { return *current_thread_; }
 
-  void Enqueue(const SharedPtr<Thread> thread) {
+  void Enqueue(const RefPtr<Thread>& thread) {
     runnable_threads_.PushBack(thread);
   }
 
@@ -25,10 +25,10 @@ class Scheduler {
  private:
   bool enabled_ = false;
 
-  SharedPtr<Thread> current_thread_;
-  LinkedList<SharedPtr<Thread>> runnable_threads_;
+  RefPtr<Thread> current_thread_;
+  LinkedList<RefPtr<Thread>> runnable_threads_;
 
-  SharedPtr<Thread> sleep_thread_;
+  RefPtr<Thread> sleep_thread_;
 
   Scheduler();
   void SwapToCurrent(Thread& prev);

zion/scheduler/thread.cpp

@@ -20,8 +20,12 @@ extern "C" void thread_init() {
 
 }  // namespace
 
-SharedPtr<Thread> Thread::RootThread(Process& root_proc) {
-  return new Thread(root_proc);
+RefPtr<Thread> Thread::RootThread(Process& root_proc) {
+  return MakeRefCounted<Thread>(root_proc);
+}
+
+RefPtr<Thread> Thread::Create(Process& proc, uint64_t tid) {
+  return MakeRefCounted<Thread>(proc, tid);
 }
 
 Thread::Thread(Process& proc, uint64_t tid) : process_(proc), id_(tid) {

zion/scheduler/thread.h

@@ -2,12 +2,13 @@
 
 #include <stdint.h>
 
-#include "lib/shared_ptr.h"
+#include "lib/ref_counted.h"
+#include "lib/ref_ptr.h"
 
 // Forward decl due to cyclic dependency.
 class Process;
 
-class Thread {
+class Thread : public RefCounted<Thread> {
  public:
   enum State {
     UNSPECIFIED,
@@ -16,9 +17,8 @@ class Thread {
     RUNNABLE,
     FINISHED,
   };
-  static SharedPtr<Thread> RootThread(Process& root_proc);
-
-  Thread(Process& proc, uint64_t tid);
+  static RefPtr<Thread> RootThread(Process& root_proc);
+  static RefPtr<Thread> Create(Process& proc, uint64_t tid);
 
   uint64_t tid() const { return id_; };
   uint64_t pid() const;
@@ -40,6 +40,8 @@ class Thread {
   void Exit();
 
  private:
+  friend class MakeRefCountedFriend<Thread>;
+  Thread(Process& proc, uint64_t tid);
   // Special constructor for the root thread only.
   Thread(Process& proc) : process_(proc), id_(0) {}
   Process& process_;