[ntcore] Match standard handle layout, only allow 16 instances (#3577)

Now that there are only 16 instances, store them all statically.

Make tests more reliable by using different ports for each connection in listener tests.

ntcore/src/main/native/cpp/Handle.h

@@ -10,8 +10,8 @@
 namespace nt {
 
 // Handle data layout:
-// Bits 30-28: Type
-// Bits 27-20: Instance index
+// Bits 30-24: Type
+// Bits 23-20: Instance index
 // Bits 19-0:  Handle index (0/unused for instance handles)
 
 class Handle {
@@ -40,15 +40,15 @@ class Handle {
       m_handle = 0;
       return;
     }
-    m_handle = ((static_cast<int>(type) & 0xf) << 27) | ((inst & 0x7f) << 20) |
+    m_handle = ((static_cast<int>(type) & 0x7f) << 24) | ((inst & 0xf) << 20) |
                (index & 0xfffff);
   }
 
   int GetIndex() const { return static_cast<int>(m_handle) & 0xfffff; }
   Type GetType() const {
-    return static_cast<Type>((static_cast<int>(m_handle) >> 27) & 0xf);
+    return static_cast<Type>((static_cast<int>(m_handle) >> 24) & 0x7f);
   }
-  int GetInst() const { return (static_cast<int>(m_handle) >> 20) & 0x7f; }
+  int GetInst() const { return (static_cast<int>(m_handle) >> 20) & 0xf; }
   bool IsType(Type type) const { return type == GetType(); }
   int GetTypedIndex(Type type) const { return IsType(type) ? GetIndex() : -1; }
   int GetTypedInst(Type type) const { return IsType(type) ? GetInst() : -1; }

ntcore/src/main/native/cpp/InstanceImpl.cpp

@@ -7,8 +7,7 @@
 using namespace nt;
 
 std::atomic<int> InstanceImpl::s_default{-1};
-std::atomic<InstanceImpl*> InstanceImpl::s_fast_instances[10];
-wpi::UidVector<InstanceImpl*, 10> InstanceImpl::s_instances;
+std::atomic<InstanceImpl*> InstanceImpl::s_instances[kNumInstances];
 wpi::mutex InstanceImpl::s_mutex;
 
 using namespace std::placeholders;
@@ -35,36 +34,10 @@ InstanceImpl* InstanceImpl::GetDefault() {
 }
 
 InstanceImpl* InstanceImpl::Get(int inst) {
-  if (inst < 0) {
+  if (inst < 0 || inst >= kNumInstances) {
     return nullptr;
   }
-
-  // fast path, just an atomic read
-  if (static_cast<unsigned int>(inst) <
-      (sizeof(s_fast_instances) / sizeof(s_fast_instances[0]))) {
-    InstanceImpl* ptr = s_fast_instances[inst];
-    if (ptr) {
-      return ptr;
-    }
-  }
-
-  // slow path
-  std::scoped_lock lock(s_mutex);
-
-  // static fast-path block
-  if (static_cast<unsigned int>(inst) <
-      (sizeof(s_fast_instances) / sizeof(s_fast_instances[0]))) {
-    // double-check
-    return s_fast_instances[inst];
-  }
-
-  // vector
-  if (static_cast<unsigned int>(inst) < s_instances.size()) {
-    return s_instances[inst];
-  }
-
-  // doesn't exist
-  return nullptr;
+  return s_instances[inst];
 }
 
 int InstanceImpl::GetDefaultIndex() {
@@ -94,28 +67,23 @@ int InstanceImpl::Alloc() {
 }
 
 int InstanceImpl::AllocImpl() {
-  unsigned int inst = s_instances.emplace_back(nullptr);
-  InstanceImpl* ptr = new InstanceImpl(inst);
-  s_instances[inst] = ptr;
-
-  if (inst < (sizeof(s_fast_instances) / sizeof(s_fast_instances[0]))) {
-    s_fast_instances[inst] = ptr;
+  int inst = 0;
+  for (; inst < kNumInstances; ++inst) {
+    if (!s_instances[inst]) {
+      s_instances[inst] = new InstanceImpl(inst);
+      return inst;
+    }
   }
-
-  return static_cast<int>(inst);
+  return -1;
 }
 
 void InstanceImpl::Destroy(int inst) {
   std::scoped_lock lock(s_mutex);
-  if (inst < 0 || static_cast<unsigned int>(inst) >= s_instances.size()) {
+  if (inst < 0 || inst >= kNumInstances) {
     return;
   }
 
-  if (static_cast<unsigned int>(inst) <
-      (sizeof(s_fast_instances) / sizeof(s_fast_instances[0]))) {
-    s_fast_instances[inst] = nullptr;
-  }
-
-  delete s_instances[inst];
-  s_instances.erase(inst);
+  InstanceImpl* ptr = nullptr;
+  s_instances[inst].exchange(ptr);
+  delete ptr;
 }

ntcore/src/main/native/cpp/InstanceImpl.h

@@ -8,7 +8,6 @@
 #include <atomic>
 #include <memory>
 
-#include <wpi/UidVector.h>
 #include <wpi/mutex.h>
 
 #include "ConnectionNotifier.h"
@@ -47,8 +46,8 @@ class InstanceImpl {
   static int AllocImpl();
 
   static std::atomic<int> s_default;
-  static std::atomic<InstanceImpl*> s_fast_instances[10];
-  static wpi::UidVector<InstanceImpl*, 10> s_instances;
+  static constexpr int kNumInstances = 16;
+  static std::atomic<InstanceImpl*> s_instances[kNumInstances];
   static wpi::mutex s_mutex;
 };