JDK14/Java14源码在线阅读
/*
* Copyright (c) 1997, 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 "code/codeCache.hpp"
#include "code/compiledIC.hpp"
#include "code/icBuffer.hpp"
#include "code/nmethod.hpp"
#include "compiler/compileBroker.hpp"
#include "gc/shared/collectedHeap.hpp"
#include "gc/shared/workgroup.hpp"
#include "jfr/jfrEvents.hpp"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/allocation.inline.hpp"
#include "memory/resourceArea.hpp"
#include "memory/universe.hpp"
#include "oops/method.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/handshake.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/orderAccess.hpp"
#include "runtime/os.hpp"
#include "runtime/sweeper.hpp"
#include "runtime/thread.inline.hpp"
#include "runtime/vmOperations.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/events.hpp"
#include "utilities/xmlstream.hpp"
#ifdef ASSERT
#define SWEEP(nm) record_sweep(nm, __LINE__)
// Sweeper logging code
class SweeperRecord {
public:
int traversal;
int compile_id;
long traversal_mark;
int state;
const char* kind;
address vep;
address uep;
int line;
void print() {
tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
PTR_FORMAT " state = %d traversal_mark %ld line = %d",
traversal,
compile_id,
kind == NULL ? "" : kind,
p2i(uep),
p2i(vep),
state,
traversal_mark,
line);
}
};
static int _sweep_index = 0;
static SweeperRecord* _records = NULL;
void NMethodSweeper::report_events(int id, address entry) {
if (_records != NULL) {
for (int i = _sweep_index; i < SweeperLogEntries; i++) {
if (_records[i].uep == entry ||
_records[i].vep == entry ||
_records[i].compile_id == id) {
_records[i].print();
}
}
for (int i = 0; i < _sweep_index; i++) {
if (_records[i].uep == entry ||
_records[i].vep == entry ||
_records[i].compile_id == id) {
_records[i].print();
}
}
}
}
void NMethodSweeper::report_events() {
if (_records != NULL) {
for (int i = _sweep_index; i < SweeperLogEntries; i++) {
// skip empty records
if (_records[i].vep == NULL) continue;
_records[i].print();
}
for (int i = 0; i < _sweep_index; i++) {
// skip empty records
if (_records[i].vep == NULL) continue;
_records[i].print();
}
}
}
void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
if (_records != NULL) {
_records[_sweep_index].traversal = _traversals;
_records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
_records[_sweep_index].compile_id = nm->compile_id();
_records[_sweep_index].kind = nm->compile_kind();
_records[_sweep_index].state = nm->get_state();
_records[_sweep_index].vep = nm->verified_entry_point();
_records[_sweep_index].uep = nm->entry_point();
_records[_sweep_index].line = line;
_sweep_index = (_sweep_index + 1) % SweeperLogEntries;
}
}
void NMethodSweeper::init_sweeper_log() {
if (LogSweeper && _records == NULL) {
// Create the ring buffer for the logging code
_records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
}
}
#else
#define SWEEP(nm)
#endif
CompiledMethodIterator NMethodSweeper::_current(CompiledMethodIterator::all_blobs); // Current compiled method
long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
volatile bool NMethodSweeper::_should_sweep = false;// Indicates if we should invoke the sweeper
volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
// 1) alive -> not_entrant
// 2) not_entrant -> zombie
int NMethodSweeper::_hotness_counter_reset_val = 0;
long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
class MarkActivationClosure: public CodeBlobClosure {
public:
virtual void do_code_blob(CodeBlob* cb) {
assert(cb->is_nmethod(), "CodeBlob should be nmethod");
nmethod* nm = (nmethod*)cb;
nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
// If we see an activation belonging to a non_entrant nmethod, we mark it.
if (nm->is_not_entrant()) {
nm->mark_as_seen_on_stack();
}
}
};
static MarkActivationClosure mark_activation_closure;
class SetHotnessClosure: public CodeBlobClosure {
public:
virtual void do_code_blob(CodeBlob* cb) {
assert(cb->is_nmethod(), "CodeBlob should be nmethod");
nmethod* nm = (nmethod*)cb;
nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
}
};
static SetHotnessClosure set_hotness_closure;
int NMethodSweeper::hotness_counter_reset_val() {
if (_hotness_counter_reset_val == 0) {
_hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
}
return _hotness_counter_reset_val;
}
bool NMethodSweeper::wait_for_stack_scanning() {
return _current.end();
}
class NMethodMarkingClosure : public HandshakeClosure {
private:
CodeBlobClosure* _cl;
public:
NMethodMarkingClosure(CodeBlobClosure* cl) : HandshakeClosure("NMethodMarking"), _cl(cl) {}
void do_thread(Thread* thread) {
if (thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) {
JavaThread* jt = (JavaThread*) thread;
jt->nmethods_do(_cl);
}
}
};
class NMethodMarkingTask : public AbstractGangTask {
private:
NMethodMarkingClosure* _cl;
public:
NMethodMarkingTask(NMethodMarkingClosure* cl) :
AbstractGangTask("Parallel NMethod Marking"),
_cl(cl) {
Threads::change_thread_claim_token();
}
~NMethodMarkingTask() {
Threads::assert_all_threads_claimed();
}
void work(uint worker_id) {
Threads::possibly_parallel_threads_do(true, _cl);
}
};
/**
* Scans the stacks of all Java threads and marks activations of not-entrant methods.
* No need to synchronize access, since 'mark_active_nmethods' is always executed at a
* safepoint.
*/
void NMethodSweeper::mark_active_nmethods() {
CodeBlobClosure* cl = prepare_mark_active_nmethods();
if (cl != NULL) {
WorkGang* workers = Universe::heap()->get_safepoint_workers();
if (workers != NULL) {
NMethodMarkingClosure tcl(cl);
NMethodMarkingTask task(&tcl);
workers->run_task(&task);
} else {
Threads::nmethods_do(cl);
}
}
}
CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
#ifdef ASSERT
if (SafepointMechanism::uses_thread_local_poll()) {
assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
assert_lock_strong(CodeCache_lock);
} else {
assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
}
#endif
// If we do not want to reclaim not-entrant or zombie methods there is no need
// to scan stacks
if (!MethodFlushing) {
return NULL;
}
// Increase time so that we can estimate when to invoke the sweeper again.
_time_counter++;
// Check for restart
assert(_current.method() == NULL, "should only happen between sweeper cycles");
assert(wait_for_stack_scanning(), "should only happen between sweeper cycles");
_seen = 0;
_current = CompiledMethodIterator(CompiledMethodIterator::all_blobs);
// Initialize to first nmethod
_current.next();
_traversals += 1;
_total_time_this_sweep = Tickspan();
if (PrintMethodFlushing) {
tty->print_cr("### Sweep: stack traversal %ld", _traversals);
}
return &mark_activation_closure;
}
CodeBlobClosure* NMethodSweeper::prepare_reset_hotness_counters() {
assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
// If we do not want to reclaim not-entrant or zombie methods there is no need
// to scan stacks
if (!MethodFlushing) {
return NULL;
}
// Increase time so that we can estimate when to invoke the sweeper again.
_time_counter++;
// Check for restart
if (_current.method() != NULL) {
if (_current.method()->is_nmethod()) {
assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
} else if (_current.method()->is_aot()) {
assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
} else {
ShouldNotReachHere();
}
}
return &set_hotness_closure;
}
/**
* This function triggers a VM operation that does stack scanning of active
* methods. Stack scanning is mandatory for the sweeper to make progress.
*/
void NMethodSweeper::do_stack_scanning() {
assert(!CodeCache_lock->owned_by_self(), "just checking");
if (wait_for_stack_scanning()) {
if (SafepointMechanism::uses_thread_local_poll()) {
CodeBlobClosure* code_cl;
{
MutexLocker ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
code_cl = prepare_mark_active_nmethods();
}
if (code_cl != NULL) {
NMethodMarkingClosure nm_cl(code_cl);
Handshake::execute(&nm_cl);
}
} else {
VM_MarkActiveNMethods op;
VMThread::execute(&op);
}
}
}
void NMethodSweeper::sweeper_loop() {
bool timeout;
while (true) {
{
ThreadBlockInVM tbivm(JavaThread::current());
MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
const long wait_time = 60*60*24 * 1000;
timeout = waiter.wait(wait_time);
}
if (!timeout) {
possibly_sweep();
}
}
}
/**
* Wakes up the sweeper thread to possibly sweep.
*/
void NMethodSweeper::notify(int code_blob_type) {
// Makes sure that we do not invoke the sweeper too often during startup.
double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
assert_locked_or_safepoint(CodeCache_lock);
CodeCache_lock->notify();
}
}
/**
* Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
*/
void NMethodSweeper::force_sweep() {
ThreadBlockInVM tbivm(JavaThread::current());
MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
// Request forced sweep
_force_sweep = true;
while (_force_sweep) {
// Notify sweeper that we want to force a sweep and wait for completion.
// In case a sweep currently takes place we timeout and try again because
// we want to enforce a full sweep.
CodeCache_lock->notify();
waiter.wait(1000);
}
}
/**
* Handle a safepoint request
*/
void NMethodSweeper::handle_safepoint_request() {
JavaThread* thread = JavaThread::current();
if (SafepointMechanism::should_block(thread)) {
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
}
MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
ThreadBlockInVM tbivm(thread);
thread->java_suspend_self();
}
}
/**
* This function invokes the sweeper if at least one of the three conditions is met:
* (1) The code cache is getting full
* (2) There are sufficient state changes in/since the last sweep.
* (3) We have not been sweeping for 'some time'
*/
void NMethodSweeper::possibly_sweep() {
assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
// If there was no state change while nmethod sweeping, 'should_sweep' will be false.
// This is one of the two places where should_sweep can be set to true. The general
// idea is as follows: If there is enough free space in the code cache, there is no
// need to invoke the sweeper. The following formula (which determines whether to invoke
// the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
// we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
// the formula considers how much space in the code cache is currently used. Here are
// some examples that will (hopefully) help in understanding.
//
// Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
// the result of the division is 0. This
// keeps the used code cache size small
// (important for embedded Java)
// Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
// computes: (256 / 16) - 1 = 15
// As a result, we invoke the sweeper after
// 15 invocations of 'mark_active_nmethods.
// Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
// computes: (256 / 16) - 10 = 6.
if (!_should_sweep) {
const int time_since_last_sweep = _time_counter - _last_sweep;
// ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
// since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
// an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
// value) that disables the intended periodic sweeps.
const int max_wait_time = ReservedCodeCacheSize / (16 * M);
double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
_should_sweep = true;
}
}
// Remember if this was a forced sweep
bool forced = _force_sweep;
// Force stack scanning if there is only 10% free space in the code cache.
// We force stack scanning only if the non-profiled code heap gets full, since critical
// allocations go to the non-profiled heap and we must be make sure that there is
// enough space.
double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
if (free_percent <= StartAggressiveSweepingAt || forced || _should_sweep) {
do_stack_scanning();
}
if (_should_sweep || forced) {
init_sweeper_log();
sweep_code_cache();
}
// We are done with sweeping the code cache once.
_total_nof_code_cache_sweeps++;
_last_sweep = _time_counter;
// Reset flag; temporarily disables sweeper
_should_sweep = false;
// If there was enough state change, 'possibly_enable_sweeper()'
// sets '_should_sweep' to true
possibly_enable_sweeper();
// Reset _bytes_changed only if there was enough state change. _bytes_changed
// can further increase by calls to 'report_state_change'.
if (_should_sweep) {
_bytes_changed = 0;
}
if (forced) {
// Notify requester that forced sweep finished
assert(_force_sweep, "Should be a forced sweep");
MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
_force_sweep = false;
CodeCache_lock->notify();
}
}
static void post_sweep_event(EventSweepCodeCache* event,
const Ticks& start,
const Ticks& end,
s4 traversals,
int swept,
int flushed,
int zombified) {
assert(event != NULL, "invariant");
assert(event->should_commit(), "invariant");
event->set_starttime(start);
event->set_endtime(end);
event->set_sweepId(traversals);
event->set_sweptCount(swept);
event->set_flushedCount(flushed);
event->set_zombifiedCount(zombified);
event->commit();
}
void NMethodSweeper::sweep_code_cache() {
ResourceMark rm;
Ticks sweep_start_counter = Ticks::now();
log_debug(codecache, sweep, start)("CodeCache flushing");
int flushed_count = 0;
int zombified_count = 0;
int flushed_c2_count = 0;
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
}
int swept_count = 0;
assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
assert(!CodeCache_lock->owned_by_self(), "just checking");
int freed_memory = 0;
{
MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
while (!_current.end()) {
swept_count++;
// 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.
CompiledMethod* nm = _current.method();
_current.next();
// Now ready to process nmethod and give up CodeCache_lock
{
MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
// Save information before potentially flushing the nmethod
// Only flushing nmethods so size only matters for them.
int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
bool is_c2_method = nm->is_compiled_by_c2();
bool is_osr = nm->is_osr_method();
int compile_id = nm->compile_id();
intptr_t address = p2i(nm);
const char* state_before = nm->state();
const char* state_after = "";
MethodStateChange type = process_compiled_method(nm);
switch (type) {
case Flushed:
state_after = "flushed";
freed_memory += size;
++flushed_count;
if (is_c2_method) {
++flushed_c2_count;
}
break;
case MadeZombie:
state_after = "made zombie";
++zombified_count;
break;
case None:
break;
default:
ShouldNotReachHere();
}
if (PrintMethodFlushing && Verbose && type != None) {
tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
}
}
_seen++;
handle_safepoint_request();
}
}
assert(_current.end(), "must have scanned the whole cache");
const Ticks sweep_end_counter = Ticks::now();
const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
{
MutexLocker mu(NMethodSweeperStats_lock, Mutex::_no_safepoint_check_flag);
_total_time_sweeping += sweep_time;
_total_time_this_sweep += sweep_time;
_peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
_total_flushed_size += freed_memory;
_total_nof_methods_reclaimed += flushed_count;
_total_nof_c2_methods_reclaimed += flushed_c2_count;
_peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
}
EventSweepCodeCache event(UNTIMED);
if (event.should_commit()) {
post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
}
#ifdef ASSERT
if(PrintMethodFlushing) {
tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
}
#endif
Log(codecache, sweep) log;
if (log.is_debug()) {
LogStream ls(log.debug());
CodeCache::print_summary(&ls, false);
}
log_sweep("finished");
// Sweeper is the only case where memory is released, check here if it
// is time to restart the compiler. Only checking if there is a certain
// amount of free memory in the code cache might lead to re-enabling
// compilation although no memory has been released. For example, there are
// cases when compilation was disabled although there is 4MB (or more) free
// memory in the code cache. The reason is code cache fragmentation. Therefore,
// it only makes sense to re-enable compilation if we have actually freed memory.
// Note that typically several kB are released for sweeping 16MB of the code
// cache. As a result, 'freed_memory' > 0 to restart the compiler.
if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
log.debug("restart compiler");
log_sweep("restart_compiler");
}
}
/**
* This function updates the sweeper statistics that keep track of nmethods
* state changes. If there is 'enough' state change, the sweeper is invoked
* as soon as possible. There can be data races on _bytes_changed. The data
* races are benign, since it does not matter if we loose a couple of bytes.
* In the worst case we call the sweeper a little later. Also, we are guaranteed
* to invoke the sweeper if the code cache gets full.
*/
void NMethodSweeper::report_state_change(nmethod* nm) {
_bytes_changed += nm->total_size();
possibly_enable_sweeper();
}
/**
* Function determines if there was 'enough' state change in the code cache to invoke
* the sweeper again. Currently, we determine 'enough' as more than 1% state change in
* the code cache since the last sweep.
*/
void NMethodSweeper::possibly_enable_sweeper() {
double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
if (percent_changed > 1.0) {
_should_sweep = true;
}
}
class CompiledMethodMarker: public StackObj {
private:
CodeCacheSweeperThread* _thread;
public:
CompiledMethodMarker(CompiledMethod* cm) {
JavaThread* current = JavaThread::current();
assert (current->is_Code_cache_sweeper_thread(), "Must be");
_thread = (CodeCacheSweeperThread*)current;
if (!cm->is_zombie() && !cm->is_unloading()) {
// Only expose live nmethods for scanning
_thread->set_scanned_compiled_method(cm);
}
}
~CompiledMethodMarker() {
_thread->set_scanned_compiled_method(NULL);
}
};
NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
assert(cm != NULL, "sanity");
assert(!CodeCache_lock->owned_by_self(), "just checking");
MethodStateChange result = None;
// Make sure this nmethod doesn't get unloaded during the scan,
// since safepoints may happen during acquired below locks.
CompiledMethodMarker nmm(cm);
SWEEP(cm);
// Skip methods that are currently referenced by the VM
if (cm->is_locked_by_vm()) {
// But still remember to clean-up inline caches for alive nmethods
if (cm->is_alive()) {
// Clean inline caches that point to zombie/non-entrant/unloaded nmethods
cm->cleanup_inline_caches(false);
SWEEP(cm);
}
return result;
}
if (cm->is_zombie()) {
// All inline caches that referred to this nmethod were cleaned in the
// previous sweeper cycle. Now flush the nmethod from the code cache.
assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
cm->flush();
assert(result == None, "sanity");
result = Flushed;
} else if (cm->is_not_entrant()) {
// If there are no current activations of this method on the
// stack we can safely convert it to a zombie method
OrderAccess::loadload(); // _stack_traversal_mark and _state
if (cm->can_convert_to_zombie()) {
// Code cache state change is tracked in make_zombie()
cm->make_zombie();
SWEEP(cm);
assert(result == None, "sanity");
result = MadeZombie;
assert(cm->is_zombie(), "nmethod must be zombie");
} else {
// Still alive, clean up its inline caches
cm->cleanup_inline_caches(false);
SWEEP(cm);
}
} else if (cm->is_unloaded()) {
// Code is unloaded, so there are no activations on the stack.
// Convert the nmethod to zombie.
// Code cache state change is tracked in make_zombie()
cm->make_zombie();
SWEEP(cm);
assert(result == None, "sanity");
result = MadeZombie;
} else {
if (cm->is_nmethod()) {
possibly_flush((nmethod*)cm);
}
// Clean inline caches that point to zombie/non-entrant/unloaded nmethods
cm->cleanup_inline_caches(false);
SWEEP(cm);
}
return result;
}
void NMethodSweeper::possibly_flush(nmethod* nm) {
if (UseCodeCacheFlushing) {
if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed() && !nm->is_unloading()) {
bool make_not_entrant = false;
// Do not make native methods not-entrant
nm->dec_hotness_counter();
// Get the initial value of the hotness counter. This value depends on the
// ReservedCodeCacheSize
int reset_val = hotness_counter_reset_val();
int time_since_reset = reset_val - nm->hotness_counter();
int code_blob_type = CodeCache::get_code_blob_type(nm);
double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
// The less free space in the code cache we have - the bigger reverse_free_ratio() is.
// I.e., 'threshold' increases with lower available space in the code cache and a higher
// NmethodSweepActivity. If the current hotness counter - which decreases from its initial
// value until it is reset by stack walking - is smaller than the computed threshold, the
// corresponding nmethod is considered for removal.
if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
// A method is marked as not-entrant if the method is
// 1) 'old enough': nm->hotness_counter() < threshold
// 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
// The second condition is necessary if we are dealing with very small code cache
// sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
// The second condition ensures that methods are not immediately made not-entrant
// after compilation.
make_not_entrant = true;
}
// The stack-scanning low-cost detection may not see the method was used (which can happen for
// flat profiles). Check the age counter for possible data.
if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
if (mc != NULL) {
// Snapshot the value as it's changed concurrently
int age = mc->nmethod_age();
if (MethodCounters::is_nmethod_hot(age)) {
// The method has gone through flushing, and it became relatively hot that it deopted
// before we could take a look at it. Give it more time to appear in the stack traces,
// proportional to the number of deopts.
MethodData* md = nm->method()->method_data();
if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
// It's been long enough, we still haven't seen it on stack.
// Try to flush it, but enable counters the next time.
mc->reset_nmethod_age();
} else {
make_not_entrant = false;
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