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/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_LOCKS_H_
#define ART_RUNTIME_LOCKS_H_
#include <ostream>
#include "base/macros.h"
namespace art {
class LOCKABLE Mutex;
class LOCKABLE ReaderWriterMutex;
// LockLevel is used to impose a lock hierarchy [1] where acquisition of a Mutex at a higher or
// equal level to a lock a thread holds is invalid. The lock hierarchy achieves a cycle free
// partial ordering and thereby cause deadlock situations to fail checks.
//
// [1] http://www.drdobbs.com/parallel/use-lock-hierarchies-to-avoid-deadlock/204801163
enum LockLevel {
kLoggingLock = 0,
kUnexpectedSignalLock,
kThreadSuspendCountLock,
kAbortLock,
kJdwpSocketLock,
kAllocSpaceLock,
kDefaultMutexLevel,
kMarkSweepLargeObjectLock,
kPinTableLock,
kLoadLibraryLock,
kJdwpObjectRegistryLock,
kClassLinkerClassesLock,
kBreakpointLock,
kThreadListLock,
kBreakpointInvokeLock,
kTraceLock,
kJdwpEventListLock,
kJdwpAttachLock,
kJdwpStartLock,
kRuntimeShutdownLock,
kHeapBitmapLock,
kMonitorLock,
kMutatorLock,
kZygoteCreationLock,
kLockLevelCount // Must come last.
};
std::ostream& operator<<(std::ostream& os, const LockLevel& rhs);
// Global mutexes corresponding to the levels above.
class Locks {
public:
static void Init();
// The mutator_lock_ is used to allow mutators to execute in a shared (reader) mode or to block
// mutators by having an exclusive (writer) owner. In normal execution each mutator thread holds
// a share on the mutator_lock_. The garbage collector may also execute with shared access but
// at times requires exclusive access to the heap (not to be confused with the heap meta-data
// guarded by the heap_lock_ below). When the garbage collector requires exclusive access it asks
// the mutators to suspend themselves which also involves usage of the thread_suspend_count_lock_
// to cover weaknesses in using ReaderWriterMutexes with ConditionVariables. We use a condition
// variable to wait upon in the suspension logic as releasing and then re-acquiring a share on
// the mutator lock doesn't necessarily allow the exclusive user (e.g the garbage collector)
// chance to acquire the lock.
//
// Thread suspension:
// Shared users | Exclusive user
// (holding mutator lock and in kRunnable state) | .. running ..
// .. running .. | Request thread suspension by:
// .. running .. | - acquiring thread_suspend_count_lock_
// .. running .. | - incrementing Thread::suspend_count_ on
// .. running .. | all mutator threads
// .. running .. | - releasing thread_suspend_count_lock_
// .. running .. | Block trying to acquire exclusive mutator lock
// Poll Thread::suspend_count_ and enter full | .. blocked ..
// suspend code. | .. blocked ..
// Change state to kSuspended | .. blocked ..
// x: Release share on mutator_lock_ | Carry out exclusive access
// Acquire thread_suspend_count_lock_ | .. exclusive ..
// while Thread::suspend_count_ > 0 | .. exclusive ..
// - wait on Thread::resume_cond_ | .. exclusive ..
// (releases thread_suspend_count_lock_) | .. exclusive ..
// .. waiting .. | Release mutator_lock_
// .. waiting .. | Request thread resumption by:
// .. waiting .. | - acquiring thread_suspend_count_lock_
// .. waiting .. | - decrementing Thread::suspend_count_ on
// .. waiting .. | all mutator threads
// .. waiting .. | - notifying on Thread::resume_cond_
// - re-acquire thread_suspend_count_lock_ | - releasing thread_suspend_count_lock_
// Release thread_suspend_count_lock_ | .. running ..
// Acquire share on mutator_lock_ | .. running ..
// - This could block but the thread still | .. running ..
// has a state of kSuspended and so this | .. running ..
// isn't an issue. | .. running ..
// Acquire thread_suspend_count_lock_ | .. running ..
// - we poll here as we're transitioning into | .. running ..
// kRunnable and an individual thread suspend | .. running ..
// request (e.g for debugging) won't try | .. running ..
// to acquire the mutator lock (which would | .. running ..
// block as we hold the mutator lock). This | .. running ..
// poll ensures that if the suspender thought | .. running ..
// we were suspended by incrementing our | .. running ..
// Thread::suspend_count_ and then reading | .. running ..
// our state we go back to waiting on | .. running ..
// Thread::resume_cond_. | .. running ..
// can_go_runnable = Thread::suspend_count_ == 0 | .. running ..
// Release thread_suspend_count_lock_ | .. running ..
// if can_go_runnable | .. running ..
// Change state to kRunnable | .. running ..
// else | .. running ..
// Goto x | .. running ..
// .. running .. | .. running ..
static ReaderWriterMutex* mutator_lock_;
// Allow reader-writer mutual exclusion on the mark and live bitmaps of the heap.
static ReaderWriterMutex* heap_bitmap_lock_ ACQUIRED_AFTER(mutator_lock_);
// Guards shutdown of the runtime.
static Mutex* runtime_shutdown_lock_ ACQUIRED_AFTER(heap_bitmap_lock_);
// The thread_list_lock_ guards ThreadList::list_. It is also commonly held to stop threads
// attaching and detaching.
static Mutex* thread_list_lock_ ACQUIRED_AFTER(runtime_shutdown_lock_);
// Guards breakpoints and single-stepping.
static Mutex* breakpoint_lock_ ACQUIRED_AFTER(thread_list_lock_);
// Guards trace requests.
static Mutex* trace_lock_ ACQUIRED_AFTER(breakpoint_lock_);
// Guards lists of classes within the class linker.
static ReaderWriterMutex* classlinker_classes_lock_ ACQUIRED_AFTER(trace_lock_);
// When declaring any Mutex add DEFAULT_MUTEX_ACQUIRED_AFTER to use annotalysis to check the code
// doesn't try to hold a higher level Mutex.
#define DEFAULT_MUTEX_ACQUIRED_AFTER ACQUIRED_AFTER(classlinker_classes_lock_)
// Have an exclusive aborting thread.
static Mutex* abort_lock_ ACQUIRED_AFTER(classlinker_classes_lock_);
// Allow mutual exclusion when manipulating Thread::suspend_count_.
// TODO: Does the trade-off of a per-thread lock make sense?
static Mutex* thread_suspend_count_lock_ ACQUIRED_AFTER(abort_lock_);
// One unexpected signal at a time lock.
static Mutex* unexpected_signal_lock_ ACQUIRED_AFTER(thread_suspend_count_lock_);
// Have an exclusive logging thread.
static Mutex* logging_lock_ ACQUIRED_AFTER(unexpected_signal_lock_);
};
} // namespace art
#endif // ART_RUNTIME_LOCKS_H_
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