hotspot/src/share/vm/runtime/sweeper.cpp - platform/libcore - Git at Google

 /*
  * Copyright (c) 1997, 2010, 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);
     }
     CodeCache::log_state(tty); tty->cr();
   }

   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);
     }
     CodeCache::log_state(xtty);
     xtty->stamp();
     xtty->end_elem();
   }
 }
	/*
	* Copyright (c) 1997, 2010, 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);
	}
	CodeCache::log_state(tty); tty->cr();
	}

	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);
	}
	CodeCache::log_state(xtty);
	xtty->stamp();
	xtty->end_elem();
	}
	}