Java example source code file (sweeper.cpp)
The sweeper.cpp Java example source code
/*
* Copyright (c) 1997, 2013, 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 "memory/resourceArea.hpp"
#include "oops/method.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 "trace/tracing.hpp"
#include "utilities/events.hpp"
#include "utilities/ticks.inline.hpp"
#include "utilities/xmlstream.hpp"
#ifdef ASSERT
#define SWEEP(nm) record_sweep(nm, __LINE__)
// Sweeper logging code
class SweeperRecord {
public:
int traversal;
int invocation;
int compile_id;
long traversal_mark;
int state;
const char* kind;
address vep;
address uep;
int line;
void print() {
tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
PTR_FORMAT " state = %d traversal_mark %d line = %d",
traversal,
invocation,
compile_id,
kind == NULL ? "" : kind,
uep,
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(nmethod* nm, int line) {
if (_records != NULL) {
_records[_sweep_index].traversal = _traversals;
_records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
_records[_sweep_index].invocation = _sweep_fractions_left;
_records[_sweep_index].compile_id = nm->compile_id();
_records[_sweep_index].kind = nm->compile_kind();
_records[_sweep_index].state = nm->_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;
}
}
#else
#define SWEEP(nm)
#endif
nmethod* NMethodSweeper::_current = NULL; // Current nmethod
long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
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
int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep
int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep
int NMethodSweeper::_marked_for_reclamation_count = 0; // Nof. nmethods marked for reclaim in current sweep
volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
volatile int NMethodSweeper::_sweep_fractions_left = 0; // Nof. invocations left until we are completed with this pass
volatile int NMethodSweeper::_sweep_started = 0; // Flag to control conc sweeper
volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
// 1) alive -> not_entrant
// 2) not_entrant -> zombie
// 3) zombie -> marked_for_reclamation
int NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
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
int NMethodSweeper::_hotness_counter_reset_val = 0;
class MarkActivationClosure: public CodeBlobClosure {
public:
virtual void do_code_blob(CodeBlob* cb) {
if (cb->is_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) {
if (cb->is_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::sweep_in_progress() {
return (_current != NULL);
}
// 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() {
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;
}
// Increase time so that we can estimate when to invoke the sweeper again.
_time_counter++;
// Check for restart
assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
if (!sweep_in_progress()) {
_seen = 0;
_sweep_fractions_left = NmethodSweepFraction;
_current = CodeCache::first_nmethod();
_traversals += 1;
_total_time_this_sweep = Tickspan();
if (PrintMethodFlushing) {
tty->print_cr("### Sweep: stack traversal %d", _traversals);
}
Threads::nmethods_do(&mark_activation_closure);
} else {
// Only set hotness counter
Threads::nmethods_do(&set_hotness_closure);
}
OrderAccess::storestore();
}
/**
* 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");
// Only compiler threads are allowed to sweep
if (!MethodFlushing || !sweep_in_progress() || !Thread::current()->is_Compiler_thread()) {
return;
}
// 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) {
int time_since_last_sweep = _time_counter - _last_sweep;
double wait_until_next_sweep = (ReservedCodeCacheSize / (16 * M)) - time_since_last_sweep -
CodeCache::reverse_free_ratio();
if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
_should_sweep = true;
}
}
if (_should_sweep && _sweep_fractions_left > 0) {
// Only one thread at a time will sweep
jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );
if (old != 0) {
return;
}
#ifdef ASSERT
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);
}
#endif
if (_sweep_fractions_left > 0) {
sweep_code_cache();
_sweep_fractions_left--;
}
// We are done with sweeping the code cache once.
if (_sweep_fractions_left == 0) {
_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;
}
}
_sweep_started = 0;
}
}
void NMethodSweeper::sweep_code_cache() {
Ticks sweep_start_counter = Ticks::now();
_flushed_count = 0;
_zombified_count = 0;
_marked_for_reclamation_count = 0;
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
}
if (!CompileBroker::should_compile_new_jobs()) {
// If we have turned off compilations we might as well do full sweeps
// in order to reach the clean state faster. Otherwise the sleeping compiler
// threads will slow down sweeping.
_sweep_fractions_left = 1;
}
// 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) / _sweep_fractions_left;
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;
{
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 || _sweep_fractions_left == 1) && _current != NULL; i++) {
swept_count++;
if (SafepointSynchronize::is_synchronizing()) { // Safepoint request
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
}
MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
assert(Thread::current()->is_Java_thread(), "should be java thread");
JavaThread* thread = (JavaThread*)Thread::current();
ThreadBlockInVM tbivm(thread);
thread->java_suspend_self();
}
// 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);
freed_memory += process_nmethod(_current);
}
_seen++;
_current = next;
}
}
assert(_sweep_fractions_left > 1 || _current == NULL, "must have scanned the whole cache");
const Ticks sweep_end_counter = Ticks::now();
const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
_total_time_sweeping += sweep_time;
_total_time_this_sweep += sweep_time;
_peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
_total_nof_methods_reclaimed += _flushed_count;
EventSweepCodeCache event(UNTIMED);
if (event.should_commit()) {
event.set_starttime(sweep_start_counter);
event.set_endtime(sweep_end_counter);
event.set_sweepIndex(_traversals);
event.set_sweepFractionIndex(NmethodSweepFraction - _sweep_fractions_left + 1);
event.set_sweptCount(swept_count);
event.set_flushedCount(_flushed_count);
event.set_markedCount(_marked_for_reclamation_count);
event.set_zombifiedCount(_zombified_count);
event.commit();
}
#ifdef ASSERT
if(PrintMethodFlushing) {
tty->print_cr("### sweeper: sweep time(%d): "
INT64_FORMAT, _sweep_fractions_left, (jlong)sweep_time.value());
}
#endif
if (_sweep_fractions_left == 1) {
_peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
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_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 NMethodMarker: public StackObj {
private:
CompilerThread* _thread;
public:
NMethodMarker(nmethod* nm) {
_thread = CompilerThread::current();
if (!nm->is_zombie() && !nm->is_unloaded()) {
// Only expose live nmethods for scanning
_thread->set_scanned_nmethod(nm);
}
}
~NMethodMarker() {
_thread->set_scanned_nmethod(NULL);
}
};
void NMethodSweeper::release_nmethod(nmethod *nm) {
// Clean up any CompiledICHolders
{
ResourceMark rm;
MutexLocker ml_patch(CompiledIC_lock);
RelocIterator iter(nm);
while (iter.next()) {
if (iter.type() == relocInfo::virtual_call_type) {
CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
}
}
}
MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
nm->flush();
}
int NMethodSweeper::process_nmethod(nmethod *nm) {
assert(!CodeCache_lock->owned_by_self(), "just checking");
int freed_memory = 0;
// Make sure this nmethod doesn't get unloaded during the scan,
// since safepoints may happen during acquired below locks.
NMethodMarker nmm(nm);
SWEEP(nm);
// 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 inline caches that point to zombie/non-entrant methods
MutexLocker cl(CompiledIC_lock);
nm->cleanup_inline_caches();
SWEEP(nm);
}
return freed_memory;
}
if (nm->is_zombie()) {
// If it is the first time we see nmethod then we mark it. Otherwise,
// we reclaim 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);
}
freed_memory = nm->total_size();
release_nmethod(nm);
_flushed_count++;
} else {
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
}
nm->mark_for_reclamation();
// Keep track of code cache state change
_bytes_changed += nm->total_size();
_marked_for_reclamation_count++;
SWEEP(nm);
}
} else if (nm->is_not_entrant()) {
// If there are 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);
}
// Code cache state change is tracked in make_zombie()
nm->make_zombie();
_zombified_count++;
SWEEP(nm);
} else {
// Still alive, clean up its inline caches
MutexLocker cl(CompiledIC_lock);
nm->cleanup_inline_caches();
SWEEP(nm);
}
} 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()) {
SWEEP(nm);
// No inline caches will ever point to osr methods, so we can just remove it
freed_memory = nm->total_size();
release_nmethod(nm);
_flushed_count++;
} else {
// Code cache state change is tracked in make_zombie()
nm->make_zombie();
_zombified_count++;
SWEEP(nm);
}
} else {
if (UseCodeCacheFlushing) {
if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
// Do not make native methods and OSR-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();
double threshold = -reset_val + (CodeCache::reverse_free_ratio() * 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 > 10)) {
// 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 > 10)
// 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.
nm->make_not_entrant();
// Code cache state change is tracked in make_not_entrant()
if (PrintMethodFlushing && Verbose) {
tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
}
}
}
}
// Clean-up all inline caches that point to zombie/non-reentrant methods
MutexLocker cl(CompiledIC_lock);
nm->cleanup_inline_caches();
SWEEP(nm);
}
return freed_memory;
}
// 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) {
stringStream s;
// Dump code cache state into a buffer before locking the tty,
// because log_state() will use locks causing lock conflicts.
CodeCache::log_state(&s);
ttyLocker ttyl;
tty->print("### sweeper: %s ", msg);
if (format != NULL) {
va_list ap;
va_start(ap, format);
tty->vprint(format, ap);
va_end(ap);
}
tty->print_cr(s.as_string());
}
if (LogCompilation && (xtty != NULL)) {
stringStream s;
// Dump code cache state into a buffer before locking the tty,
// because log_state() will use locks causing lock conflicts.
CodeCache::log_state(&s);
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->print(s.as_string());
xtty->stamp();
xtty->end_elem();
}
}
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