Mercurial > hg > graal-jvmci-8
view src/share/vm/runtime/sweeper.cpp @ 1716:be3f9c242c9d
6948538: CMS: BOT walkers can fall into object allocation and initialization cracks
Summary: GC workers now recognize an intermediate transient state of blocks which are allocated but have not yet completed initialization. blk_start() calls do not attempt to determine the size of a block in the transient state, rather waiting for the block to become initialized so that it is safe to query its size. Audited and ensured the order of initialization of object fields (klass, free bit and size) to respect block state transition protocol. Also included some new assertion checking code enabled in debug mode.
Reviewed-by: chrisphi, johnc, poonam
author | ysr |
---|---|
date | Mon, 16 Aug 2010 15:58:42 -0700 |
parents | 8d5934a77f10 |
children | d5d065957597 |
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/* * 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 "incls/_precompiled.incl" # include "incls/_sweeper.cpp.incl" 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 nm->method()->invocation_counter()->decay(); nm->method()->backedge_counter()->decay(); 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); } tty->print_cr(" total_blobs='" UINT32_FORMAT "' nmethods='" UINT32_FORMAT "'" " adapters='" UINT32_FORMAT "' free_code_cache='" SIZE_FORMAT "'", CodeCache::nof_blobs(), CodeCache::nof_nmethods(), CodeCache::nof_adapters(), CodeCache::unallocated_capacity()); } 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->print(" total_blobs='" UINT32_FORMAT "' nmethods='" UINT32_FORMAT "'" " adapters='" UINT32_FORMAT "' free_code_cache='" SIZE_FORMAT "'", CodeCache::nof_blobs(), CodeCache::nof_nmethods(), CodeCache::nof_adapters(), CodeCache::unallocated_capacity()); xtty->stamp(); xtty->end_elem(); } }