[Zion] Add a mutex object with appropriate syscalls.

zion/object/mutex.cpp

@@ -0,0 +1,30 @@
+#include "object/mutex.h"
+
+#include "scheduler/scheduler.h"
+
+glcr::RefPtr<Mutex> Mutex::Create() {
+  return glcr::AdoptPtr<Mutex>(new Mutex());
+}
+
+// FIXME: We almost certainly have some race conditions
+// between this and unlock where we could end up with
+// a thread in the blocked_threads_ queue while noone is holding the lock.
+void Mutex::Lock() {
+  while (__atomic_fetch_or(&lock_, 0x1, __ATOMIC_SEQ_CST) == 0x1) {
+    auto thread = gScheduler->CurrentThread();
+    thread->SetState(Thread::BLOCKED);
+    blocked_threads_.PushBack(thread);
+    gScheduler->Yield();
+  }
+}
+
+// FIXME: Check that this thread is the one that is holding the mutex before
+// releasing it.
+void Mutex::Release() {
+  lock_ = 0;
+  if (blocked_threads_.size() > 0) {
+    auto thread = blocked_threads_.PopFront();
+    thread->SetState(Thread::RUNNABLE);
+    gScheduler->Enqueue(thread);
+  }
+}