8253694: Remove Thread::muxAcquire() from ThreadCrashProtection()

Reviewed-by: dholmes, dcubed, coleenp

src/hotspot/os/posix/os_posix.cpp

@@ -1525,9 +1525,10 @@ bool os::Posix::matches_effective_uid_and_gid_or_root(uid_t uid, gid_t gid) {
 
 Thread* os::ThreadCrashProtection::_protected_thread = NULL;
 os::ThreadCrashProtection* os::ThreadCrashProtection::_crash_protection = NULL;
-volatile intptr_t os::ThreadCrashProtection::_crash_mux = 0;
 
 os::ThreadCrashProtection::ThreadCrashProtection() {
+  _protected_thread = Thread::current();
+  assert(_protected_thread->is_JfrSampler_thread(), "should be JFRSampler");
 }
 
 /*
@@ -1539,11 +1540,6 @@ os::ThreadCrashProtection::ThreadCrashProtection() {
 bool os::ThreadCrashProtection::call(os::CrashProtectionCallback& cb) {
   sigset_t saved_sig_mask;
 
-  Thread::muxAcquire(&_crash_mux, "CrashProtection");
-
-  _protected_thread = Thread::current_or_null();
-  assert(_protected_thread != NULL, "Cannot crash protect a NULL thread");
-
   // we cannot rely on sigsetjmp/siglongjmp to save/restore the signal mask
   // since on at least some systems (OS X) siglongjmp will restore the mask
   // for the process, not the thread
@@ -1556,14 +1552,12 @@ bool os::ThreadCrashProtection::call(os::CrashProtectionCallback& cb) {
     // and clear the crash protection
     _crash_protection = NULL;
     _protected_thread = NULL;
-    Thread::muxRelease(&_crash_mux);
     return true;
   }
   // this happens when we siglongjmp() back
   pthread_sigmask(SIG_SETMASK, &saved_sig_mask, NULL);
   _crash_protection = NULL;
   _protected_thread = NULL;
-  Thread::muxRelease(&_crash_mux);
   return false;
 }
 

src/hotspot/os/posix/os_posix.hpp

@@ -146,7 +146,7 @@ class Posix {
 };
 
 /*
- * Crash protection for the watcher thread. Wrap the callback
+ * Crash protection for the JfrSampler thread. Wrap the callback
  * with a sigsetjmp and in case of a SIGSEGV/SIGBUS we siglongjmp
  * back.
  * To be able to use this - don't take locks, don't rely on destructors,
@@ -167,7 +167,6 @@ class ThreadCrashProtection : public StackObj {
 private:
   static Thread* _protected_thread;
   static ThreadCrashProtection* _crash_protection;
-  static volatile intptr_t _crash_mux;
   void restore();
   sigjmp_buf _jmpbuf;
 };

src/hotspot/os/windows/os_windows.cpp

@@ -5066,9 +5066,10 @@ void os::pause() {
 
 Thread* os::ThreadCrashProtection::_protected_thread = NULL;
 os::ThreadCrashProtection* os::ThreadCrashProtection::_crash_protection = NULL;
-volatile intptr_t os::ThreadCrashProtection::_crash_mux = 0;
 
 os::ThreadCrashProtection::ThreadCrashProtection() {
+  _protected_thread = Thread::current();
+  assert(_protected_thread->is_JfrSampler_thread(), "should be JFRSampler");
 }
 
 // See the caveats for this class in os_windows.hpp
@@ -5078,12 +5079,6 @@ os::ThreadCrashProtection::ThreadCrashProtection() {
 // The callback is supposed to provide the method that should be protected.
 //
 bool os::ThreadCrashProtection::call(os::CrashProtectionCallback& cb) {
-
-  Thread::muxAcquire(&_crash_mux, "CrashProtection");
-
-  _protected_thread = Thread::current_or_null();
-  assert(_protected_thread != NULL, "Cannot crash protect a NULL thread");
-
   bool success = true;
   __try {
     _crash_protection = this;
@@ -5094,7 +5089,6 @@ bool os::ThreadCrashProtection::call(os::CrashProtectionCallback& cb) {
   }
   _crash_protection = NULL;
   _protected_thread = NULL;
-  Thread::muxRelease(&_crash_mux);
   return success;
 }
 

src/hotspot/os/windows/os_windows.hpp

@@ -128,7 +128,7 @@ class win32 {
 };
 
 /*
- * Crash protection for the watcher thread. Wrap the callback
+ * Crash protection for the JfrSampler thread. Wrap the callback
  * with a __try { call() }
  * To be able to use this - don't take locks, don't rely on destructors,
  * don't make OS library calls, don't allocate memory, don't print,
@@ -146,7 +146,6 @@ class ThreadCrashProtection : public StackObj {
 private:
   static Thread* _protected_thread;
   static ThreadCrashProtection* _crash_protection;
-  static volatile intptr_t _crash_mux;
 };
 
 class PlatformEvent : public CHeapObj<mtSynchronizer> {

src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp

@@ -343,6 +343,7 @@ class JfrThreadSampler : public NonJavaThread {
   virtual void post_run();
  public:
   virtual char* name() const { return (char*)"JFR Thread Sampler"; }
+  bool is_JfrSampler_thread() const { return true; }
   void run();
   static Monitor* transition_block() { return JfrThreadSampler_lock; }
   static void on_javathread_suspend(JavaThread* thread);

src/hotspot/share/runtime/thread.hpp

@@ -490,6 +490,7 @@ class Thread: public ThreadShadow {
   virtual bool is_ConcurrentGC_thread() const        { return false; }
   virtual bool is_Named_thread() const               { return false; }
   virtual bool is_Worker_thread() const              { return false; }
+  virtual bool is_JfrSampler_thread() const          { return false; }
 
   // Can this thread make Java upcalls
   virtual bool can_call_java() const                 { return false; }