8350667: Remove startThread_lock() and _startThread_lock on AIX

Reviewed-by: stuefe, jkern

src/hotspot/os/aix/osThread_aix.cpp

@@ -37,11 +37,9 @@ OSThread::OSThread()
     _siginfo(nullptr),
     _ucontext(nullptr),
     _expanding_stack(0),
-    _alt_sig_stack(nullptr),
-    _startThread_lock(new Monitor(Mutex::event, "startThread_lock")) {
+    _alt_sig_stack(nullptr) {
   sigemptyset(&_caller_sigmask);
 }
 
 OSThread::~OSThread() {
-  delete _startThread_lock;
 }

src/hotspot/os/aix/osThread_aix.hpp

@@ -114,15 +114,6 @@ class OSThread : public OSThreadBase {
   void set_alt_sig_stack(address val)     { _alt_sig_stack = val; }
   address alt_sig_stack(void)             { return _alt_sig_stack; }
 
- private:
-  Monitor* _startThread_lock;     // sync parent and child in thread creation
-
- public:
-
-  Monitor* startThread_lock() const {
-    return _startThread_lock;
-  }
-
   // Printing
   uintx thread_id_for_printing() const override {
     return (uintx)_thread_id;

src/hotspot/os/aix/os_aix.cpp

@@ -796,6 +796,8 @@ bool os::create_thread(Thread* thread, ThreadType thr_type,
   // OSThread::thread_id is the pthread id.
   osthread->set_thread_id(tid);
 
+  // child thread synchronization is not done here on AIX, a thread is started in suspended state
+
   return true;
 }