pipeline: Fix `Thread::bind_thread()` regression

Fixes #1575

panda/src/pipeline/thread.cxx

@@ -92,16 +92,19 @@ Thread::
  */
 PT(Thread) Thread::
 bind_thread(const std::string &name, const std::string &sync_name) {
-  Thread *current_thread = get_current_thread();
-  if (current_thread != get_external_thread()) {
+  PT(Thread) thread = new ExternalThread(name, sync_name);
+#ifndef HAVE_THREADS
+  Thread *current_thread = get_main_thread();
+#else
+  Thread *current_thread = ThreadImpl::bind_thread(thread);
+#endif
+  if (current_thread != nullptr &&
+      current_thread != thread.p()) {
     // This thread already has an associated thread.
     nassertr(current_thread->get_name() == name &&
              current_thread->get_sync_name() == sync_name, current_thread);
-    return current_thread;
+    thread = current_thread;
   }
-
-  PT(Thread) thread = new ExternalThread(name, sync_name);
-  ThreadImpl::bind_thread(thread);
   return thread;
 }
 

panda/src/pipeline/threadDummyImpl.I

@@ -63,13 +63,15 @@ prepare_for_exit() {
 }
 
 /**
- * Associates the indicated Thread object with the currently-executing thread.
+ * Associates the indicated Thread object with the currently-executing thread,
+ * unless a thread is already bound, in which case it is returned.
  * You should not call this directly; use Thread::bind_thread() instead.
  */
-INLINE void ThreadDummyImpl::
+INLINE Thread *ThreadDummyImpl::
 bind_thread(Thread *thread) {
   // This method shouldn't be called in the non-threaded case.
-  nassertv(false);
+  nassertr(false, nullptr);
+  return nullptr;
 }
 
 /**

panda/src/pipeline/threadDummyImpl.h

@@ -55,7 +55,7 @@ public:
   INLINE static void prepare_for_exit();
 
   static Thread *get_current_thread();
-  INLINE static void bind_thread(Thread *thread);
+  INLINE static Thread *bind_thread(Thread *thread);
   INLINE static bool is_threading_supported();
   INLINE static bool is_true_threads();
   INLINE static bool is_simple_threads();

panda/src/pipeline/threadPosixImpl.cxx

@@ -193,18 +193,23 @@ get_unique_id() const {
 }
 
 /**
- * Associates the indicated Thread object with the currently-executing thread.
+ * Associates the indicated Thread object with the currently-executing thread,
+ * unless a thread is already bound, in which case it is returned.
  * You should not call this directly; use Thread::bind_thread() instead.
  */
-void ThreadPosixImpl::
+Thread *ThreadPosixImpl::
 bind_thread(Thread *thread) {
-  if (_current_thread == nullptr && thread == Thread::get_main_thread()) {
+  if (_current_thread != nullptr) {
+    return _current_thread;
+  }
+  if (thread == Thread::get_main_thread()) {
     _main_thread_known.test_and_set(std::memory_order_relaxed);
   }
   _current_thread = thread;
 #ifdef ANDROID
   bind_java_thread();
 #endif
+  return thread;
 }
 
 #ifdef ANDROID

panda/src/pipeline/threadPosixImpl.h

@@ -49,7 +49,7 @@ public:
   INLINE static void prepare_for_exit();
 
   INLINE static Thread *get_current_thread();
-  static void bind_thread(Thread *thread);
+  static Thread *bind_thread(Thread *thread);
   INLINE static bool is_threading_supported();
   INLINE static bool is_true_threads();
   INLINE static bool is_simple_threads();

panda/src/pipeline/threadSimpleImpl.I

@@ -36,11 +36,13 @@ is_same_system_thread() const {
 }
 
 /**
- * Associates the indicated Thread object with the currently-executing thread.
+ * Associates the indicated Thread object with the currently-executing thread,
+ * unless a thread is already bound, in which case it is returned.
  * You should not call this directly; use Thread::bind_thread() instead.
  */
-INLINE void ThreadSimpleImpl::
+INLINE Thread *ThreadSimpleImpl::
 bind_thread(Thread *) {
+  return get_current_thread();
 }
 
 /**

panda/src/pipeline/threadSimpleImpl.h

@@ -61,7 +61,7 @@ public:
   INLINE static Thread *get_current_thread();
   INLINE bool is_same_system_thread() const;
 
-  INLINE static void bind_thread(Thread *thread);
+  INLINE static Thread *bind_thread(Thread *thread);
   INLINE static bool is_threading_supported();
   static bool is_true_threads();
   INLINE static bool is_simple_threads();

panda/src/pipeline/threadWin32Impl.cxx

@@ -184,15 +184,20 @@ get_current_thread() {
 }
 
 /**
- * Associates the indicated Thread object with the currently-executing thread.
+ * Associates the indicated Thread object with the currently-executing thread,
+ * unless a thread is already bound, in which case it is returned.
  * You should not call this directly; use Thread::bind_thread() instead.
  */
-void ThreadWin32Impl::
+Thread *ThreadWin32Impl::
 bind_thread(Thread *thread) {
-  if (_current_thread == nullptr && thread == Thread::get_main_thread()) {
+  if (_current_thread != nullptr) {
+    return _current_thread;
+  }
+  if (thread == Thread::get_main_thread()) {
     _main_thread_known.test_and_set(std::memory_order_relaxed);
   }
   _current_thread = thread;
+  return thread;
 }
 
 /**

panda/src/pipeline/threadWin32Impl.h

@@ -44,7 +44,7 @@ public:
   INLINE static void prepare_for_exit();
 
   static Thread *get_current_thread();
-  static void bind_thread(Thread *thread);
+  static Thread *bind_thread(Thread *thread);
   INLINE static bool is_threading_supported();
   INLINE static bool is_true_threads();
   INLINE static bool is_simple_threads();