/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

#include "precompiled.hpp"

#include "logging/log.hpp"

#include "runtime/interfaceSupport.inline.hpp"

#include "runtime/os.hpp"

#include "services/attachListener.hpp"

#include "services/dtraceAttacher.hpp"

#include <windows.h>

#include <signal.h>             // SIGBREAK

#include <stdio.h>

// The AttachListener thread services a queue of operations. It blocks in the dequeue

// function until an operation is enqueued. A client enqueues an operation by creating

// a thread in this process using the Win32 CreateRemoteThread function. That thread

// executes a small stub generated by the client. The stub invokes the

// JVM_EnqueueOperation function which checks the operation parameters and enqueues

// the operation to the queue serviced by the attach listener. The thread created by

// the client is a native thread and is restricted to a single page of stack. To keep

// it simple operations are pre-allocated at initialization time. An enqueue thus

// takes a preallocated operation, populates the operation parameters, adds it to

// queue and wakes up the attach listener.

//

// When an operation has completed the attach listener is required to send the

// operation result and any result data to the client. In this implementation the

// client is a pipe server. In the enqueue operation it provides the name of pipe

// to this process. When the operation is completed this process opens the pipe and

// sends the result and output back to the client. Note that writing to the pipe

// (and flushing the output) is a blocking operation. This means that a non-responsive

// client could potentially hang the attach listener thread indefinitely. In that

// case no new operations would be executed but the VM would continue as normal.

// As only suitably privileged processes can open this process we concluded that

// this wasn't worth worrying about.

// forward reference

class Win32AttachOperation;

class Win32AttachListener: AllStatic {

 private:

  enum {

    max_enqueued_operations = 4

  };

  // protects the preallocated list and the operation list

  static HANDLE _mutex;

  // head of preallocated operations list

  static Win32AttachOperation* _avail;

  // head and tail of enqueue operations list

  static Win32AttachOperation* _head;

  static Win32AttachOperation* _tail;

  static Win32AttachOperation* head()                       { return _head; }

  static void set_head(Win32AttachOperation* head)          { _head = head; }

  static Win32AttachOperation* tail()                       { return _tail; }

  static void set_tail(Win32AttachOperation* tail)          { _tail = tail; }

  // A semaphore is used for communication about enqueued operations.

  // The maximum count for the semaphore object will be set to "max_enqueued_operations".

  // The state of a semaphore is signaled when its count is greater than

  // zero (there are operations enqueued), and nonsignaled when it is zero.

  static HANDLE _enqueued_ops_semaphore;

  static HANDLE enqueued_ops_semaphore() { return _enqueued_ops_semaphore; }

 public:

  enum {

    ATTACH_ERROR_DISABLED               = 100,              // error codes

    ATTACH_ERROR_RESOURCE               = 101,

    ATTACH_ERROR_ILLEGALARG             = 102,

    ATTACH_ERROR_INTERNAL               = 103

  };

  static int init();

  static HANDLE mutex()                                     { return _mutex; }

  static Win32AttachOperation* available()                  { return _avail; }

  static void set_available(Win32AttachOperation* avail)    { _avail = avail; }

  // enqueue an operation to the end of the list

  static int enqueue(char* cmd, char* arg1, char* arg2, char* arg3, char* pipename);

  // dequeue an operation from from head of the list

  static Win32AttachOperation* dequeue();

};

// statics

HANDLE Win32AttachListener::_mutex;

HANDLE Win32AttachListener::_enqueued_ops_semaphore;

Win32AttachOperation* Win32AttachListener::_avail;

Win32AttachOperation* Win32AttachListener::_head;

Win32AttachOperation* Win32AttachListener::_tail;

// Win32AttachOperation is an AttachOperation that additionally encapsulates the name

// of a pipe which is used to send the operation reply/output to the client.

// Win32AttachOperation can also be linked in a list.

class Win32AttachOperation: public AttachOperation {

 private:

  friend class Win32AttachListener;

  enum {

    pipe_name_max = 256             // maximum pipe name

  };

  char _pipe[pipe_name_max + 1];

  const char* pipe() const                              { return _pipe; }

  void set_pipe(const char* pipe) {

    assert(strlen(pipe) <= pipe_name_max, "exceeds maximum length of pipe name");

    os::snprintf(_pipe, sizeof(_pipe), "%s", pipe);

  }

  HANDLE open_pipe();

  static BOOL write_pipe(HANDLE hPipe, char* buf, int len);

  Win32AttachOperation* _next;

  Win32AttachOperation* next() const                    { return _next; }

  void set_next(Win32AttachOperation* next)             { _next = next; }

  // noarg constructor as operation is preallocated

  Win32AttachOperation() : AttachOperation("<noname>") {

    set_pipe("<nopipe>");

    set_next(NULL);

  }

 public:

  void Win32AttachOperation::complete(jint result, bufferedStream* result_stream);

};

// Preallocate the maximum number of operations that can be enqueued.

int Win32AttachListener::init() {

  _mutex = (void*)::CreateMutex(NULL, FALSE, NULL);

  guarantee(_mutex != (HANDLE)NULL, "mutex creation failed");

  _enqueued_ops_semaphore = ::CreateSemaphore(NULL, 0, max_enqueued_operations, NULL);

  guarantee(_enqueued_ops_semaphore != (HANDLE)NULL, "semaphore creation failed");

  set_head(NULL);

  set_tail(NULL);

  set_available(NULL);

  for (int i=0; i<max_enqueued_operations; i++) {

    Win32AttachOperation* op = new Win32AttachOperation();

    op->set_next(available());

    set_available(op);

  }

  return 0;

}

// Enqueue an operation. This is called from a native thread that is not attached to VM.

// Also we need to be careful not to execute anything that results in more than a 4k stack.

//

int Win32AttachListener::enqueue(char* cmd, char* arg0, char* arg1, char* arg2, char* pipename) {

  // wait up to 10 seconds for listener to be up and running

  int sleep_count = 0;

  while (!AttachListener::is_initialized()) {

    Sleep(1000); // 1 second

    sleep_count++;

    if (sleep_count > 10) { // try for 10 seconds

      return ATTACH_ERROR_DISABLED;

    }

  }

  // check that all paramteres to the operation

  if (strlen(cmd) > AttachOperation::name_length_max) return ATTACH_ERROR_ILLEGALARG;

  if (strlen(arg0) > AttachOperation::arg_length_max) return ATTACH_ERROR_ILLEGALARG;

  if (strlen(arg1) > AttachOperation::arg_length_max) return ATTACH_ERROR_ILLEGALARG;

  if (strlen(arg2) > AttachOperation::arg_length_max) return ATTACH_ERROR_ILLEGALARG;

  if (strlen(pipename) > Win32AttachOperation::pipe_name_max) return ATTACH_ERROR_ILLEGALARG;

  // check for a well-formed pipename

  if (strstr(pipename, "\\\\.\\pipe\\") != pipename) return ATTACH_ERROR_ILLEGALARG;

  // grab the lock for the list

  DWORD res = ::WaitForSingleObject(mutex(), INFINITE);

  if (res != WAIT_OBJECT_0) {

    return ATTACH_ERROR_INTERNAL;

  }

  // try to get an operation from the available list

  Win32AttachOperation* op = available();

  if (op != NULL) {

    set_available(op->next());

    // add to end (tail) of list

    op->set_next(NULL);

    if (tail() == NULL) {

      set_head(op);

    } else {

      tail()->set_next(op);

    }

    set_tail(op);

    op->set_name(cmd);

    op->set_arg(0, arg0);

    op->set_arg(1, arg1);

    op->set_arg(2, arg2);

    op->set_pipe(pipename);

    // Increment number of enqueued operations.

    // Side effect: Semaphore will be signaled and will release

    // any blocking waiters (i.e. the AttachListener thread).

    BOOL not_exceeding_semaphore_maximum_count =

      ::ReleaseSemaphore(enqueued_ops_semaphore(), 1, NULL);

    guarantee(not_exceeding_semaphore_maximum_count, "invariant");

  }

  ::ReleaseMutex(mutex());

  return (op != NULL) ? 0 : ATTACH_ERROR_RESOURCE;

}

// dequeue the operation from the head of the operation list.

Win32AttachOperation* Win32AttachListener::dequeue() {

  for (;;) {

    DWORD res = ::WaitForSingleObject(enqueued_ops_semaphore(), INFINITE);

    // returning from WaitForSingleObject will have decreased

    // the current count of the semaphore by 1.

    guarantee(res == WAIT_OBJECT_0, "wait failed");

    res = ::WaitForSingleObject(mutex(), INFINITE);

    guarantee(res == WAIT_OBJECT_0, "wait failed");

    Win32AttachOperation* op = head();

    if (op != NULL) {

      set_head(op->next());

      if (head() == NULL) {     // list is empty

        set_tail(NULL);

      }

    }

    ::ReleaseMutex(mutex());

    if (op != NULL) {

      return op;

    }

  }

}

// open the pipe to the client

HANDLE Win32AttachOperation::open_pipe() {

                        GENERIC_WRITE,   // write only

                        0,              // no sharing

                        NULL,           // default security attributes

                        OPEN_EXISTING,  // opens existing pipe

                        0,              // default attributes

                        NULL);          // no template file

  return hPipe;

}

// write to the pipe

BOOL Win32AttachOperation::write_pipe(HANDLE hPipe, char* buf, int len) {

  do {

    DWORD nwrote;

    BOOL fSuccess = WriteFile(  hPipe,                  // pipe handle

                                (LPCVOID)buf,           // message

                                (DWORD)len,             // message length

                                &nwrote,                // bytes written

                                NULL);                  // not overlapped

    if (!fSuccess) {

      return fSuccess;

    }

    buf += nwrote;

    len -= nwrote;

  return TRUE;

}

// Complete the operation:

//   - open the pipe to the client

//   - write the operation result (a jint)

//   - write the operation output (the result stream)

//

void Win32AttachOperation::complete(jint result, bufferedStream* result_stream) {

  JavaThread* thread = JavaThread::current();

  ThreadBlockInVM tbivm(thread);

  thread->set_suspend_equivalent();

  // cleared by handle_special_suspend_equivalent_condition() or

  // java_suspend_self() via check_and_wait_while_suspended()

  HANDLE hPipe = open_pipe();

  if (hPipe != INVALID_HANDLE_VALUE) {

    BOOL fSuccess;

    char msg[32];

    _snprintf(msg, sizeof(msg), "%d\n", result);

    msg[sizeof(msg) - 1] = '\0';

    fSuccess = write_pipe(hPipe, msg, (int)strlen(msg));

    if (fSuccess) {

      fSuccess = write_pipe(hPipe, (char*)result_stream->base(), (int)(result_stream->size()));

    }

    // Need to flush buffers

    FlushFileBuffers(hPipe);

    CloseHandle(hPipe);

    if (fSuccess) {

      log_debug(attach)("wrote result of attach operation %s to pipe %s", name(), pipe());

    } else {

    }

  } else {

  }

  DWORD res = ::WaitForSingleObject(Win32AttachListener::mutex(), INFINITE);

  if (res == WAIT_OBJECT_0) {

    // put the operation back on the available list

    set_next(Win32AttachListener::available());

    Win32AttachListener::set_available(this);

    ::ReleaseMutex(Win32AttachListener::mutex());

  }

  // were we externally suspended while we were waiting?

  thread->check_and_wait_while_suspended();

}

// AttachOperation functions

AttachOperation* AttachListener::dequeue() {

  JavaThread* thread = JavaThread::current();

  ThreadBlockInVM tbivm(thread);

  thread->set_suspend_equivalent();

  // cleared by handle_special_suspend_equivalent_condition() or

  // java_suspend_self() via check_and_wait_while_suspended()

  AttachOperation* op = Win32AttachListener::dequeue();

  // were we externally suspended while we were waiting?

  thread->check_and_wait_while_suspended();

  return op;

}

void AttachListener::vm_start() {

  // nothing to do

}

int AttachListener::pd_init() {

  return Win32AttachListener::init();

}

bool AttachListener::init_at_startup() {

  return true;

}

// no trigger mechanism on Windows to start Attach Listener lazily

bool AttachListener::is_init_trigger() {

  return false;

}

void AttachListener::abort() {

  // nothing to do

}

void AttachListener::pd_data_dump() {

  os::signal_notify(SIGBREAK);

}

AttachOperationFunctionInfo* AttachListener::pd_find_operation(const char* n) {

  return NULL;

}

jint AttachListener::pd_set_flag(AttachOperation* op, outputStream* out) {

  out->print_cr("flag '%s' cannot be changed", op->arg(0));

  return JNI_ERR;

}

void AttachListener::pd_detachall() {

  // do nothing for now

}

// Native thread started by remote client executes this.

extern "C" {

  JNIEXPORT jint JNICALL

    JVM_EnqueueOperation(char* cmd, char* arg0, char* arg1, char* arg2, char* pipename) {

      return (jint)Win32AttachListener::enqueue(cmd, arg0, arg1, arg2, pipename);

    }

} // extern