/*

 * Copyright (c) 1997, 2011, 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 "code/codeCache.hpp"

#include "code/nmethod.hpp"

#include "compiler/compileBroker.hpp"

#include "memory/resourceArea.hpp"

#include "oops/methodOop.hpp"

#include "runtime/atomic.hpp"

#include "runtime/compilationPolicy.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/os.hpp"

#include "runtime/sweeper.hpp"

#include "runtime/vm_operations.hpp"

#include "utilities/events.hpp"

#include "utilities/xmlstream.hpp"

long      NMethodSweeper::_traversals = 0;   // No. of stack traversals performed

nmethod*  NMethodSweeper::_current = NULL;   // Current nmethod

int       NMethodSweeper::_seen = 0 ;        // No. of nmethods we have currently processed in current pass of CodeCache

volatile int NMethodSweeper::_invocations = 0;   // No. of invocations left until we are completed with this pass

volatile int NMethodSweeper::_sweep_started = 0; // Whether a sweep is in progress.

jint      NMethodSweeper::_locked_seen = 0;

jint      NMethodSweeper::_not_entrant_seen_on_stack = 0;

bool      NMethodSweeper::_rescan = false;

bool      NMethodSweeper::_do_sweep = false;

bool      NMethodSweeper::_was_full = false;

jint      NMethodSweeper::_advise_to_sweep = 0;

jlong     NMethodSweeper::_last_was_full = 0;

uint      NMethodSweeper::_highest_marked = 0;

long      NMethodSweeper::_was_full_traversal = 0;

class MarkActivationClosure: public CodeBlobClosure {

public:

  virtual void do_code_blob(CodeBlob* cb) {

    // If we see an activation belonging to a non_entrant nmethod, we mark it.

    if (cb->is_nmethod() && ((nmethod*)cb)->is_not_entrant()) {

      ((nmethod*)cb)->mark_as_seen_on_stack();

    }

  }

};

static MarkActivationClosure mark_activation_closure;

void NMethodSweeper::scan_stacks() {

  assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");

  if (!MethodFlushing) return;

  _do_sweep = true;

  // No need to synchronize access, since this is always executed at a

  // safepoint.  If we aren't in the middle of scan and a rescan

  // hasn't been requested then just return. If UseCodeCacheFlushing is on and

  // code cache flushing is in progress, don't skip sweeping to help make progress

  // clearing space in the code cache.

  if ((_current == NULL && !_rescan) && !(UseCodeCacheFlushing && !CompileBroker::should_compile_new_jobs())) {

    _do_sweep = false;

    return;

  }

  // Make sure CompiledIC_lock in unlocked, since we might update some

  // inline caches. If it is, we just bail-out and try later.

  if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return;

  // Check for restart

  assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");

  if (_current == NULL) {

    _seen        = 0;

    _invocations = NmethodSweepFraction;

    _current     = CodeCache::first_nmethod();

    _traversals  += 1;

    if (PrintMethodFlushing) {

      tty->print_cr("### Sweep: stack traversal %d", _traversals);

    }

    Threads::nmethods_do(&mark_activation_closure);

    // reset the flags since we started a scan from the beginning.

    _rescan = false;

    _locked_seen = 0;

    _not_entrant_seen_on_stack = 0;

  }

  if (UseCodeCacheFlushing) {

    if (!CodeCache::needs_flushing()) {

      // scan_stacks() runs during a safepoint, no race with setters

      _advise_to_sweep = 0;

    }

    if (was_full()) {

      // There was some progress so attempt to restart the compiler

      jlong now           = os::javaTimeMillis();

      jlong max_interval  = (jlong)MinCodeCacheFlushingInterval * (jlong)1000;

      jlong curr_interval = now - _last_was_full;

      if ((!CodeCache::needs_flushing()) && (curr_interval > max_interval)) {

        CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);

        set_was_full(false);

        // Update the _last_was_full time so we can tell how fast the

        // code cache is filling up

        _last_was_full = os::javaTimeMillis();

        log_sweep("restart_compiler");

      }

    }

  }

}

void NMethodSweeper::possibly_sweep() {

  assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");

  if ((!MethodFlushing) || (!_do_sweep)) return;

  if (_invocations > 0) {

    // Only one thread at a time will sweep

    jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );

    if (old != 0) {

      return;

    }

    if (_invocations > 0) {

      sweep_code_cache();

      _invocations--;

    }

    _sweep_started = 0;

  }

}

void NMethodSweeper::sweep_code_cache() {

#ifdef ASSERT

  jlong sweep_start;

  if (PrintMethodFlushing) {

    sweep_start = os::javaTimeMillis();

  }

#endif

  if (PrintMethodFlushing && Verbose) {

    tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _invocations);

  }

  // We want to visit all nmethods after NmethodSweepFraction

  // invocations so divide the remaining number of nmethods by the

  // remaining number of invocations.  This is only an estimate since

  // the number of nmethods changes during the sweep so the final

  // stage must iterate until it there are no more nmethods.

  int todo = (CodeCache::nof_nmethods() - _seen) / _invocations;

  assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");

  assert(!CodeCache_lock->owned_by_self(), "just checking");

  {

    MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);

    // The last invocation iterates until there are no more nmethods

    for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) {

      // Since we will give up the CodeCache_lock, always skip ahead

      // to the next nmethod.  Other blobs can be deleted by other

      // threads but nmethods are only reclaimed by the sweeper.

      nmethod* next = CodeCache::next_nmethod(_current);

      // Now ready to process nmethod and give up CodeCache_lock

      {

        MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);

        process_nmethod(_current);

      }

      _seen++;

      _current = next;

    }

  }

  assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache");

  if (_current == NULL && !_rescan && (_locked_seen || _not_entrant_seen_on_stack)) {

    // we've completed a scan without making progress but there were

    // nmethods we were unable to process either because they were

    // locked or were still on stack.  We don't have to aggresively

    // clean them up so just stop scanning.  We could scan once more

    // but that complicates the control logic and it's unlikely to

    // matter much.

    if (PrintMethodFlushing) {

      tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep");

    }

  }

#ifdef ASSERT

  if(PrintMethodFlushing) {

    jlong sweep_end             = os::javaTimeMillis();

    tty->print_cr("### sweeper:      sweep time(%d): " INT64_FORMAT, _invocations, sweep_end - sweep_start);

  }

#endif

  if (_invocations == 1) {

    log_sweep("finished");

  }

}

void NMethodSweeper::process_nmethod(nmethod *nm) {

  assert(!CodeCache_lock->owned_by_self(), "just checking");

  // Skip methods that are currently referenced by the VM

  if (nm->is_locked_by_vm()) {

    // But still remember to clean-up inline caches for alive nmethods

    if (nm->is_alive()) {

      // Clean-up all inline caches that points to zombie/non-reentrant methods

      MutexLocker cl(CompiledIC_lock);

      nm->cleanup_inline_caches();

    } else {

      _locked_seen++;

    }

    return;

  }

  if (nm->is_zombie()) {

    // If it is first time, we see nmethod then we mark it. Otherwise,

    // we reclame it. When we have seen a zombie method twice, we know that

    // there are no inline caches that refer to it.

    if (nm->is_marked_for_reclamation()) {

      assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");

      if (PrintMethodFlushing && Verbose) {

        tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);

      }

      MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);

      nm->flush();

    } else {

      if (PrintMethodFlushing && Verbose) {

        tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);

      }

      nm->mark_for_reclamation();

      _rescan = true;

    }

  } else if (nm->is_not_entrant()) {

    // If there is no current activations of this method on the

    // stack we can safely convert it to a zombie method

    if (nm->can_not_entrant_be_converted()) {

      if (PrintMethodFlushing && Verbose) {

        tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);

      }

      nm->make_zombie();

      _rescan = true;

    } else {

      // Still alive, clean up its inline caches

      MutexLocker cl(CompiledIC_lock);

      nm->cleanup_inline_caches();

      // we coudn't transition this nmethod so don't immediately

      // request a rescan.  If this method stays on the stack for a

      // long time we don't want to keep rescanning the code cache.

      _not_entrant_seen_on_stack++;

    }

  } else if (nm->is_unloaded()) {

    // Unloaded code, just make it a zombie

    if (PrintMethodFlushing && Verbose)

      tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);

    if (nm->is_osr_method()) {

      // No inline caches will ever point to osr methods, so we can just remove it

      MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);

      nm->flush();

    } else {

      nm->make_zombie();

      _rescan = true;

    }

  } else {

    assert(nm->is_alive(), "should be alive");

    if (UseCodeCacheFlushing) {

      if ((nm->method()->code() != nm) && !(nm->is_locked_by_vm()) && !(nm->is_osr_method()) &&

          (_traversals > _was_full_traversal+2) && (((uint)nm->compile_id()) < _highest_marked) &&

          CodeCache::needs_flushing()) {

        // This method has not been called since the forced cleanup happened

        nm->make_not_entrant();

      }

    }

    // Clean-up all inline caches that points to zombie/non-reentrant methods

    MutexLocker cl(CompiledIC_lock);

    nm->cleanup_inline_caches();

  }

}

// Code cache unloading: when compilers notice the code cache is getting full,

// they will call a vm op that comes here. This code attempts to speculatively

// unload the oldest half of the nmethods (based on the compile job id) by

// saving the old code in a list in the CodeCache. Then

// execution resumes. If a method so marked is not called by the second sweeper

// stack traversal after the current one, the nmethod will be marked non-entrant and

// got rid of by normal sweeping. If the method is called, the methodOop's

// _code field is restored and the methodOop/nmethod

// go back to their normal state.

void NMethodSweeper::handle_full_code_cache(bool is_full) {

  // Only the first one to notice can advise us to start early cleaning

  if (!is_full){

    jint old = Atomic::cmpxchg( 1, &_advise_to_sweep, 0 );

    if (old != 0) {

      return;

    }

  }

  if (is_full) {

    // Since code cache is full, immediately stop new compiles

    bool did_set = CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation);

    if (!did_set) {

      // only the first to notice can start the cleaning,

      // others will go back and block

      return;

    }

    set_was_full(true);

    // If we run out within MinCodeCacheFlushingInterval of the last unload time, give up

    jlong now = os::javaTimeMillis();

    jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000;

    jlong curr_interval = now - _last_was_full;

    if (curr_interval < max_interval) {

      _rescan = true;

      log_sweep("disable_compiler", "flushing_interval='" UINT64_FORMAT "'",

                           curr_interval/1000);

      return;

    }

  }

  VM_HandleFullCodeCache op(is_full);

  VMThread::execute(&op);

  // rescan again as soon as possible

  _rescan = true;

}

void NMethodSweeper::speculative_disconnect_nmethods(bool is_full) {

  // If there was a race in detecting full code cache, only run

  // one vm op for it or keep the compiler shut off

  debug_only(jlong start = os::javaTimeMillis();)

  if ((!was_full()) && (is_full)) {

    if (!CodeCache::needs_flushing()) {

      log_sweep("restart_compiler");

      CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);

      return;

    }

  }

  // Traverse the code cache trying to dump the oldest nmethods

  uint curr_max_comp_id = CompileBroker::get_compilation_id();

  uint flush_target = ((curr_max_comp_id - _highest_marked) >> 1) + _highest_marked;

  log_sweep("start_cleaning");

  nmethod* nm = CodeCache::alive_nmethod(CodeCache::first());

  jint disconnected = 0;

  jint made_not_entrant  = 0;

  while ((nm != NULL)){

    uint curr_comp_id = nm->compile_id();

    // OSR methods cannot be flushed like this. Also, don't flush native methods

    // since they are part of the JDK in most cases

    if (nm->is_in_use() && (!nm->is_osr_method()) && (!nm->is_locked_by_vm()) &&

        (!nm->is_native_method()) && ((curr_comp_id < flush_target))) {

      if ((nm->method()->code() == nm)) {

        // This method has not been previously considered for

        // unloading or it was restored already

        CodeCache::speculatively_disconnect(nm);

        disconnected++;

      } else if (nm->is_speculatively_disconnected()) {

        // This method was previously considered for preemptive unloading and was not called since then

        CompilationPolicy::policy()->delay_compilation(nm->method());

        nm->make_not_entrant();

        made_not_entrant++;

      }

      if (curr_comp_id > _highest_marked) {

        _highest_marked = curr_comp_id;

      }

    }

    nm = CodeCache::alive_nmethod(CodeCache::next(nm));

  }

  log_sweep("stop_cleaning",

                       "disconnected='" UINT32_FORMAT "' made_not_entrant='" UINT32_FORMAT "'",

                       disconnected, made_not_entrant);

  // Shut off compiler. Sweeper will start over with a new stack scan and

  // traversal cycle and turn it back on if it clears enough space.

  if (was_full()) {

    _last_was_full = os::javaTimeMillis();

    CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation);

  }

  // After two more traversals the sweeper will get rid of unrestored nmethods

  _was_full_traversal = _traversals;

#ifdef ASSERT

  jlong end = os::javaTimeMillis();

  if(PrintMethodFlushing && Verbose) {

    tty->print_cr("### sweeper: unload time: " INT64_FORMAT, end-start);

  }

#endif

}

// Print out some state information about the current sweep and the

// state of the code cache if it's requested.

void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {

  if (PrintMethodFlushing) {

    ttyLocker ttyl;

    tty->print("### sweeper: %s ", msg);

    if (format != NULL) {

      va_list ap;

      va_start(ap, format);

      tty->vprint(format, ap);

      va_end(ap);

    }

  }

  if (LogCompilation && (xtty != NULL)) {

    ttyLocker ttyl;

    xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());

    if (format != NULL) {

      va_list ap;

      va_start(ap, format);

      xtty->vprint(format, ap);

      va_end(ap);

    }

    xtty->stamp();

    xtty->end_elem();

  }

}