view src/hotspot/share/runtime/mutex.cpp @ 54938:5d20b085d893

8203469: Faster safepoints Reviewed-by: dcubed, pchilanomate, dholmes, acorn, coleenp, eosterlund
author rehn
date Fri, 15 Feb 2019 14:15:10 +0100
parents 043ae846819f
children 941db9c0b5b5
line wrap: on
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/*
 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "logging/log.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/mutex.hpp"
#include "runtime/osThread.hpp"
#include "runtime/safepointMechanism.inline.hpp"
#include "runtime/thread.inline.hpp"
#include "utilities/events.hpp"
#include "utilities/macros.hpp"


void Monitor::lock(Thread * self) {
  // Ensure that the Monitor requires/allows safepoint checks.
  assert(_safepoint_check_required != Monitor::_safepoint_check_never,
         "This lock should never have a safepoint check: %s", name());

#ifdef CHECK_UNHANDLED_OOPS
  // Clear unhandled oops in JavaThreads so we get a crash right away.
  if (self->is_Java_thread()) {
    self->clear_unhandled_oops();
  }
#endif // CHECK_UNHANDLED_OOPS

  DEBUG_ONLY(check_prelock_state(self, StrictSafepointChecks));
  assert(_owner != self, "invariant");

  Monitor* in_flight_monitor = NULL;
  DEBUG_ONLY(int retry_cnt = 0;)
  while (!_lock.try_lock()) {
    // The lock is contended

  #ifdef ASSERT
    check_block_state(self);
    if (retry_cnt++ > 3) {
      log_trace(vmmonitor)("JavaThread " INTPTR_FORMAT " on %d attempt trying to acquire vmmonitor %s", p2i(self), retry_cnt, _name);
    }
  #endif // ASSERT

    if (self->is_Java_thread()) {
      assert(rank() > Mutex::special, "Potential deadlock with special or lesser rank mutex");
      { ThreadBlockInVMWithDeadlockCheck tbivmdc((JavaThread *) self, &in_flight_monitor);
        in_flight_monitor = this;  // save for ~ThreadBlockInVMWithDeadlockCheck
        _lock.lock();
      }
      if (in_flight_monitor != NULL) {
        // Not unlocked by ~ThreadBlockInVMWithDeadlockCheck
        break;
      }
    } else {
      _lock.lock();
      break;
    }
  }

  assert_owner(NULL);
  set_owner(self);
}

void Monitor::lock() {
  this->lock(Thread::current());
}

// Lock without safepoint check - a degenerate variant of lock() for use by
// JavaThreads when it is known to be safe to not check for a safepoint when
// acquiring this lock. If the thread blocks acquiring the lock it is not
// safepoint-safe and so will prevent a safepoint from being reached. If used
// in the wrong way this can lead to a deadlock with the safepoint code.

void Monitor::lock_without_safepoint_check(Thread * self) {
  // Ensure that the Monitor does not require safepoint checks.
  assert(_safepoint_check_required != Monitor::_safepoint_check_always,
         "This lock should always have a safepoint check: %s", name());
  assert(_owner != self, "invariant");
  _lock.lock();
  assert_owner(NULL);
  set_owner(self);
}

void Monitor::lock_without_safepoint_check() {
  lock_without_safepoint_check(Thread::current());
}


// Returns true if thread succeeds in grabbing the lock, otherwise false.

bool Monitor::try_lock() {
  Thread * const self = Thread::current();
  DEBUG_ONLY(check_prelock_state(self, false);)

  if (_lock.try_lock()) {
    assert_owner(NULL);
    set_owner(self);
    return true;
  }
  return false;
}

void Monitor::release_for_safepoint() {
  assert_owner(NULL);
  _lock.unlock();
}

void Monitor::unlock() {
  assert_owner(Thread::current());
  set_owner(NULL);
  _lock.unlock();
}

void Monitor::notify() {
  assert_owner(Thread::current());
  _lock.notify();
}

void Monitor::notify_all() {
  assert_owner(Thread::current());
  _lock.notify_all();
}

bool Monitor::wait(bool no_safepoint_check, long timeout,
                   bool as_suspend_equivalent) {
  // Make sure safepoint checking is used properly.
  assert(!(_safepoint_check_required == Monitor::_safepoint_check_never && no_safepoint_check == false),
         "This lock should never have a safepoint check: %s", name());
  assert(!(_safepoint_check_required == Monitor::_safepoint_check_always && no_safepoint_check == true),
         "This lock should always have a safepoint check: %s", name());

  // timeout is in milliseconds - with zero meaning never timeout
  assert(timeout >= 0, "negative timeout");

  Thread * const self = Thread::current();
  assert_owner(self);

  // as_suspend_equivalent logically implies !no_safepoint_check
  guarantee(!as_suspend_equivalent || !no_safepoint_check, "invariant");
  // !no_safepoint_check logically implies java_thread
  guarantee(no_safepoint_check || self->is_Java_thread(), "invariant");

  #ifdef ASSERT
  Monitor * least = get_least_ranked_lock_besides_this(self->owned_locks());
  assert(least != this, "Specification of get_least_... call above");
  if (least != NULL && least->rank() <= special) {
    ::tty->print("Attempting to wait on monitor %s/%d while holding"
               " lock %s/%d -- possible deadlock",
               name(), rank(), least->name(), least->rank());
    assert(false, "Shouldn't block(wait) while holding a lock of rank special");
  }
  #endif // ASSERT

  int wait_status;
  // conceptually set the owner to NULL in anticipation of
  // abdicating the lock in wait
  set_owner(NULL);
  if (no_safepoint_check) {
    wait_status = _lock.wait(timeout);
    set_owner(self);
  } else {
    assert(self->is_Java_thread(), "invariant");
    JavaThread *jt = (JavaThread *)self;
    Monitor* in_flight_monitor = NULL;

    {
      ThreadBlockInVMWithDeadlockCheck tbivmdc(jt, &in_flight_monitor);
      OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */);
      if (as_suspend_equivalent) {
        jt->set_suspend_equivalent();
        // cleared by handle_special_suspend_equivalent_condition() or
        // java_suspend_self()
      }

      wait_status = _lock.wait(timeout);
      in_flight_monitor = this;  // save for ~ThreadBlockInVMWithDeadlockCheck

      // were we externally suspended while we were waiting?
      if (as_suspend_equivalent && jt->handle_special_suspend_equivalent_condition()) {
        // Our event wait has finished and we own the lock, but
        // while we were waiting another thread suspended us. We don't
        // want to hold the lock while suspended because that
        // would surprise the thread that suspended us.
        _lock.unlock();
        jt->java_suspend_self();
        _lock.lock();
      }
    }

    if (in_flight_monitor != NULL) {
      // Not unlocked by ~ThreadBlockInVMWithDeadlockCheck
      assert_owner(NULL);
      // Conceptually reestablish ownership of the lock.
      set_owner(self);
    } else {
      lock(self);
    }
  }
  return wait_status != 0;          // return true IFF timeout
}


// Temporary JVM_RawMonitor* support.
// Yet another degenerate version of Monitor::lock() or lock_without_safepoint_check()
// jvm_raw_lock() and _unlock() can be called by non-Java threads via JVM_RawMonitorEnter.
// There's no expectation that JVM_RawMonitors will interoperate properly with the native
// Mutex-Monitor constructs.  We happen to implement JVM_RawMonitors in terms of
// native Mutex-Monitors simply as a matter of convenience.

void Monitor::jvm_raw_lock() {
  _lock.lock();
  assert_owner(NULL);
}

void Monitor::jvm_raw_unlock() {
  assert_owner(NULL);
  _lock.unlock();
}

Monitor::~Monitor() {
  assert_owner(NULL);
}

void Monitor::ClearMonitor(Monitor * m, const char *name) {
  m->_owner             = NULL;
  if (name == NULL) {
    strcpy(m->_name, "UNKNOWN");
  } else {
    strncpy(m->_name, name, MONITOR_NAME_LEN - 1);
    m->_name[MONITOR_NAME_LEN - 1] = '\0';
  }
}

Monitor::Monitor() {
  assert(os::mutex_init_done(), "Too early!");
  ClearMonitor(this);
}

Monitor::Monitor(int Rank, const char * name, bool allow_vm_block,
                 SafepointCheckRequired safepoint_check_required) {
  assert(os::mutex_init_done(), "Too early!");
  ClearMonitor(this, name);
#ifdef ASSERT
  _allow_vm_block  = allow_vm_block;
  _rank            = Rank;
  NOT_PRODUCT(_safepoint_check_required = safepoint_check_required;)
#endif
}

Mutex::Mutex(int Rank, const char * name, bool allow_vm_block,
             SafepointCheckRequired safepoint_check_required) {
  ClearMonitor((Monitor *) this, name);
#ifdef ASSERT
  _allow_vm_block   = allow_vm_block;
  _rank             = Rank;
  NOT_PRODUCT(_safepoint_check_required = safepoint_check_required;)
#endif
}

bool Monitor::owned_by_self() const {
  return _owner == Thread::current();
}

void Monitor::print_on_error(outputStream* st) const {
  st->print("[" PTR_FORMAT, p2i(this));
  st->print("] %s", _name);
  st->print(" - owner thread: " PTR_FORMAT, p2i(_owner));
}

// ----------------------------------------------------------------------------------
// Non-product code

#ifndef PRODUCT
void Monitor::print_on(outputStream* st) const {
  st->print_cr("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT,
               p2i(this), _name, p2i(_owner));
}
#endif

#ifndef PRODUCT
#ifdef ASSERT

void Monitor::assert_owner(Thread * expected) {
  const char* msg = "invalid owner";
  if (expected == NULL) {
    msg = "should be un-owned";
  }
  else if (expected == Thread::current()) {
    msg = "should be owned by current thread";
  }
  assert(_owner == expected,
         "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT,
         msg, p2i(_owner), p2i(expected));
}

Monitor * Monitor::get_least_ranked_lock(Monitor * locks) {
  Monitor *res, *tmp;
  for (res = tmp = locks; tmp != NULL; tmp = tmp->next()) {
    if (tmp->rank() < res->rank()) {
      res = tmp;
    }
  }
  if (!SafepointSynchronize::is_at_safepoint()) {
    // In this case, we expect the held locks to be
    // in increasing rank order (modulo any native ranks)
    for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
      if (tmp->next() != NULL) {
        assert(tmp->rank() == Mutex::native ||
               tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
      }
    }
  }
  return res;
}

Monitor* Monitor::get_least_ranked_lock_besides_this(Monitor* locks) {
  Monitor *res, *tmp;
  for (res = NULL, tmp = locks; tmp != NULL; tmp = tmp->next()) {
    if (tmp != this && (res == NULL || tmp->rank() < res->rank())) {
      res = tmp;
    }
  }
  if (!SafepointSynchronize::is_at_safepoint()) {
    // In this case, we expect the held locks to be
    // in increasing rank order (modulo any native ranks)
    for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
      if (tmp->next() != NULL) {
        assert(tmp->rank() == Mutex::native ||
               tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
      }
    }
  }
  return res;
}


bool Monitor::contains(Monitor* locks, Monitor * lock) {
  for (; locks != NULL; locks = locks->next()) {
    if (locks == lock) {
      return true;
    }
  }
  return false;
}
#endif

// Called immediately after lock acquisition or release as a diagnostic
// to track the lock-set of the thread and test for rank violations that
// might indicate exposure to deadlock.
// Rather like an EventListener for _owner (:>).

void Monitor::set_owner_implementation(Thread *new_owner) {
  // This function is solely responsible for maintaining
  // and checking the invariant that threads and locks
  // are in a 1/N relation, with some some locks unowned.
  // It uses the Mutex::_owner, Mutex::_next, and
  // Thread::_owned_locks fields, and no other function
  // changes those fields.
  // It is illegal to set the mutex from one non-NULL
  // owner to another--it must be owned by NULL as an
  // intermediate state.

  if (new_owner != NULL) {
    // the thread is acquiring this lock

    assert(new_owner == Thread::current(), "Should I be doing this?");
    assert(_owner == NULL, "setting the owner thread of an already owned mutex");
    _owner = new_owner; // set the owner

    // link "this" into the owned locks list

#ifdef ASSERT  // Thread::_owned_locks is under the same ifdef
    Monitor* locks = get_least_ranked_lock(new_owner->owned_locks());
    // Mutex::set_owner_implementation is a friend of Thread

    assert(this->rank() >= 0, "bad lock rank");

    // Deadlock avoidance rules require us to acquire Mutexes only in
    // a global total order. For example m1 is the lowest ranked mutex
    // that the thread holds and m2 is the mutex the thread is trying
    // to acquire, then deadlock avoidance rules require that the rank
    // of m2 be less than the rank of m1.
    // The rank Mutex::native  is an exception in that it is not subject
    // to the verification rules.
    if (this->rank() != Mutex::native &&
        this->rank() != Mutex::suspend_resume &&
        locks != NULL && locks->rank() <= this->rank() &&
        !SafepointSynchronize::is_at_safepoint()) {
      new_owner->print_owned_locks();
      fatal("acquiring lock %s/%d out of order with lock %s/%d -- "
            "possible deadlock", this->name(), this->rank(),
            locks->name(), locks->rank());
    }

    this->_next = new_owner->_owned_locks;
    new_owner->_owned_locks = this;
#endif

  } else {
    // the thread is releasing this lock

    Thread* old_owner = _owner;
    DEBUG_ONLY(_last_owner = old_owner;)

    assert(old_owner != NULL, "removing the owner thread of an unowned mutex");
    assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");

    _owner = NULL; // set the owner

#ifdef ASSERT
    Monitor *locks = old_owner->owned_locks();

    // remove "this" from the owned locks list

    Monitor *prev = NULL;
    bool found = false;
    for (; locks != NULL; prev = locks, locks = locks->next()) {
      if (locks == this) {
        found = true;
        break;
      }
    }
    assert(found, "Removing a lock not owned");
    if (prev == NULL) {
      old_owner->_owned_locks = _next;
    } else {
      prev->_next = _next;
    }
    _next = NULL;
#endif
  }
}


// Factored out common sanity checks for locking mutex'es. Used by lock() and try_lock()
void Monitor::check_prelock_state(Thread *thread, bool safepoint_check) {
  if (safepoint_check) {
    assert((!thread->is_Java_thread() || ((JavaThread *)thread)->thread_state() == _thread_in_vm)
           || rank() == Mutex::special, "wrong thread state for using locks");
    if (thread->is_VM_thread() && !allow_vm_block()) {
      fatal("VM thread using lock %s (not allowed to block on)", name());
    }
    DEBUG_ONLY(if (rank() != Mutex::special) \
               thread->check_for_valid_safepoint_state(false);)
  }
  assert(!os::ThreadCrashProtection::is_crash_protected(thread),
         "locking not allowed when crash protection is set");
}

void Monitor::check_block_state(Thread *thread) {
  if (!_allow_vm_block && thread->is_VM_thread()) {
    warning("VM thread blocked on lock");
    print();
    BREAKPOINT;
  }
  assert(_owner != thread, "deadlock: blocking on monitor owned by current thread");
}

#endif // PRODUCT