8292351: tty should always live

Reviewed-by: clanger, coleenp, dholmes

Author: tstuefe

src/hotspot/share/utilities/ostream.cpp

@@ -421,8 +421,19 @@ stringStream::~stringStream() {
   }
 }
 
+// tty needs to be always accessible since there are code paths that may write to it
+// outside of the VM lifespan.
+// Examples for pre-VM-init accesses: Early NMT init, Early UL init
+// Examples for post-VM-exit accesses: many, e.g. NMT C-heap bounds checker, signal handling, AGCT, ...
+// During lifetime tty is served by an instance of defaultStream. That instance's deletion cannot
+// be (easily) postponed or omitted since it has ties to the JVM infrastructure.
+// The policy followed here is a compromise reached during review of JDK-8292351:
+// - pre-init: we silently swallow all output. We won't see anything, but at least won't crash
+// - post-exit: we write to a simple fdStream, but somewhat mimic the behavior of the real defaultStream
+static nullStream tty_preinit_stream;
+outputStream* tty = &tty_preinit_stream;
+
 xmlStream*   xtty;
-outputStream* tty;
 extern Mutex* tty_lock;
 
 #define EXTRACHARLEN   32
@@ -615,6 +626,9 @@ void fileStream::flush() {
   }
 }
 
+fdStream fdStream::_stdout_stream(1);
+fdStream fdStream::_stderr_stream(2);
+
 void fdStream::write(const char* s, size_t len) {
   if (_fd != -1) {
     // Make an unused local variable to avoid warning from gcc compiler.
@@ -961,13 +975,13 @@ void ostream_exit() {
   if (ostream_exit_called)  return;
   ostream_exit_called = true;
   ClassListWriter::delete_classlist();
-  if (tty != defaultStream::instance) {
-    delete tty;
-  }
-  if (defaultStream::instance != NULL) {
-    delete defaultStream::instance;
+  // Make sure tty works after VM exit by assigning an always-on functioning fdStream.
+  outputStream* tmp = tty;
+  tty = DisplayVMOutputToStderr ? fdStream::stdout_stream() : fdStream::stderr_stream();
+  if (tmp != &tty_preinit_stream && tmp != defaultStream::instance) {
+    delete tmp;
   }
-  tty = NULL;
+  delete defaultStream::instance;
   xtty = NULL;
   defaultStream::instance = NULL;
 }

src/hotspot/share/utilities/ostream.hpp

@@ -248,13 +248,26 @@ class fileStream : public outputStream {
 class fdStream : public outputStream {
  protected:
   int  _fd;
+  static fdStream _stdout_stream;
+  static fdStream _stderr_stream;
  public:
   fdStream(int fd = -1) : _fd(fd) { }
   bool is_open() const { return _fd != -1; }
   void set_fd(int fd) { _fd = fd; }
   int fd() const { return _fd; }
   virtual void write(const char* c, size_t len);
   void flush() {};
+
+  // predefined streams for unbuffered IO to stdout, stderr
+  static fdStream* stdout_stream() { return &_stdout_stream; }
+  static fdStream* stderr_stream() { return &_stderr_stream; }
+};
+
+// A /dev/null equivalent stream
+class nullStream : public outputStream {
+public:
+  void write(const char* c, size_t len) {}
+  void flush() {};
 };
 
 void ostream_init();