| /* |
| * Copyright (c) 1998, 2017, 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. |
| * |
| */ |
| |
| #ifndef SHARE_VM_RUNTIME_MUTEX_HPP |
| #define SHARE_VM_RUNTIME_MUTEX_HPP |
| |
| #include "memory/allocation.hpp" |
| #include "runtime/os.hpp" |
| #include "utilities/histogram.hpp" |
| |
| // The SplitWord construct allows us to colocate the contention queue |
| // (cxq) with the lock-byte. The queue elements are ParkEvents, which are |
| // always aligned on 256-byte addresses - the least significant byte of |
| // a ParkEvent is always 0. Colocating the lock-byte with the queue |
| // allows us to easily avoid what would otherwise be a race in lock() |
| // if we were to use two completely separate fields for the contention queue |
| // and the lock indicator. Specifically, colocation renders us immune |
| // from the race where a thread might enqueue itself in the lock() slow-path |
| // immediately after the lock holder drops the outer lock in the unlock() |
| // fast-path. |
| // |
| // Colocation allows us to use a fast-path unlock() form that uses |
| // A MEMBAR instead of a CAS. MEMBAR has lower local latency than CAS |
| // on many platforms. |
| // |
| // See: |
| // + http://blogs.sun.com/dave/entry/biased_locking_in_hotspot |
| // + http://blogs.sun.com/dave/resource/synchronization-public2.pdf |
| // |
| // Note that we're *not* using word-tearing the classic sense. |
| // The lock() fast-path will CAS the lockword and the unlock() |
| // fast-path will store into the lock-byte colocated within the lockword. |
| // We depend on the fact that all our reference platforms have |
| // coherent and atomic byte accesses. More precisely, byte stores |
| // interoperate in a safe, sane, and expected manner with respect to |
| // CAS, ST and LDs to the full-word containing the byte. |
| // If you're porting HotSpot to a platform where that isn't the case |
| // then you'll want change the unlock() fast path from: |
| // STB;MEMBAR #storeload; LDN |
| // to a full-word CAS of the lockword. |
| |
| |
| union SplitWord { // full-word with separately addressable LSB |
| volatile intptr_t FullWord ; |
| volatile void * Address ; |
| volatile jbyte Bytes [sizeof(intptr_t)] ; |
| } ; |
| |
| // Endian-ness ... index of least-significant byte in SplitWord.Bytes[] |
| #ifdef VM_LITTLE_ENDIAN |
| #define _LSBINDEX 0 |
| #else |
| #define _LSBINDEX (sizeof(intptr_t)-1) |
| #endif |
| |
| class ParkEvent ; |
| |
| // See orderAccess.hpp. We assume throughout the VM that mutex lock and |
| // try_lock do fence-lock-acquire, and that unlock does a release-unlock, |
| // *in that order*. If their implementations change such that these |
| // assumptions are violated, a whole lot of code will break. |
| |
| // The default length of monitor name was originally chosen to be 64 to avoid |
| // false sharing. Now, PaddedMonitor is available for this purpose. |
| // TODO: Check if _name[MONITOR_NAME_LEN] should better get replaced by const char*. |
| static const int MONITOR_NAME_LEN = 64; |
| |
| class Monitor : public CHeapObj<mtInternal> { |
| |
| public: |
| // A special lock: Is a lock where you are guaranteed not to block while you are |
| // holding it, i.e., no vm operation can happen, taking other (blocking) locks, etc. |
| // The rank 'access' is similar to 'special' and has the same restrictions on usage. |
| // It is reserved for locks that may be required in order to perform memory accesses |
| // that require special barriers, e.g. SATB GC barriers, that in turn uses locks. |
| // Since memory accesses should be able to be performed pretty much anywhere |
| // in the code, that requires locks required for performing accesses being |
| // inherently a bit more special than even locks of the 'special' rank. |
| // NOTE: It is critical that the rank 'special' be the lowest (earliest) |
| // (except for "event" and "access") for the deadlock detection to work correctly. |
| // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate, |
| // which being external to the VM are not subject to deadlock detection. |
| // The rank safepoint is used only for synchronization in reaching a |
| // safepoint and leaving a safepoint. It is only used for the Safepoint_lock |
| // currently. While at a safepoint no mutexes of rank safepoint are held |
| // by any thread. |
| // The rank named "leaf" is probably historical (and should |
| // be changed) -- mutexes of this rank aren't really leaf mutexes |
| // at all. |
| enum lock_types { |
| event, |
| access = event + 1, |
| special = access + 2, |
| suspend_resume = special + 1, |
| leaf = suspend_resume + 2, |
| safepoint = leaf + 10, |
| barrier = safepoint + 1, |
| nonleaf = barrier + 1, |
| max_nonleaf = nonleaf + 900, |
| native = max_nonleaf + 1 |
| }; |
| |
| // The WaitSet and EntryList linked lists are composed of ParkEvents. |
| // I use ParkEvent instead of threads as ParkEvents are immortal and |
| // type-stable, meaning we can safely unpark() a possibly stale |
| // list element in the unlock()-path. |
| |
| protected: // Monitor-Mutex metadata |
| SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte |
| enum LockWordBits { _LBIT=1 } ; |
| Thread * volatile _owner; // The owner of the lock |
| // Consider sequestering _owner on its own $line |
| // to aid future synchronization mechanisms. |
| ParkEvent * volatile _EntryList ; // List of threads waiting for entry |
| ParkEvent * volatile _OnDeck ; // heir-presumptive |
| volatile intptr_t _WaitLock [1] ; // Protects _WaitSet |
| ParkEvent * volatile _WaitSet ; // LL of ParkEvents |
| volatile bool _snuck; // Used for sneaky locking (evil). |
| int NotifyCount ; // diagnostic assist |
| char _name[MONITOR_NAME_LEN]; // Name of mutex |
| |
| // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode) |
| #ifndef PRODUCT |
| bool _allow_vm_block; |
| debug_only(int _rank;) // rank (to avoid/detect potential deadlocks) |
| debug_only(Monitor * _next;) // Used by a Thread to link up owned locks |
| debug_only(Thread* _last_owner;) // the last thread to own the lock |
| debug_only(static bool contains(Monitor * locks, Monitor * lock);) |
| debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);) |
| debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);) |
| #endif |
| |
| void set_owner_implementation(Thread* owner) PRODUCT_RETURN; |
| void check_prelock_state (Thread* thread) PRODUCT_RETURN; |
| void check_block_state (Thread* thread) PRODUCT_RETURN; |
| |
| // platform-dependent support code can go here (in os_<os_family>.cpp) |
| public: |
| enum { |
| _no_safepoint_check_flag = true, |
| _allow_vm_block_flag = true, |
| _as_suspend_equivalent_flag = true |
| }; |
| |
| // Locks can be acquired with or without safepoint check. |
| // Monitor::lock and Monitor::lock_without_safepoint_check |
| // checks these flags when acquiring a lock to ensure |
| // consistent checking for each lock. |
| // A few existing locks will sometimes have a safepoint check and |
| // sometimes not, but these locks are set up in such a way to avoid deadlocks. |
| enum SafepointCheckRequired { |
| _safepoint_check_never, // Monitors with this value will cause errors |
| // when acquired with a safepoint check. |
| _safepoint_check_sometimes, // Certain locks are called sometimes with and |
| // sometimes without safepoint checks. These |
| // locks will not produce errors when locked. |
| _safepoint_check_always // Causes error if locked without a safepoint |
| // check. |
| }; |
| |
| NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;) |
| |
| enum WaitResults { |
| CONDVAR_EVENT, // Wait returned because of condition variable notification |
| INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted |
| NUMBER_WAIT_RESULTS |
| }; |
| |
| private: |
| int TrySpin (Thread * Self) ; |
| int TryLock () ; |
| int TryFast () ; |
| int AcquireOrPush (ParkEvent * ev) ; |
| void IUnlock (bool RelaxAssert) ; |
| void ILock (Thread * Self) ; |
| int IWait (Thread * Self, jlong timo); |
| int ILocked () ; |
| |
| protected: |
| static void ClearMonitor (Monitor * m, const char* name = NULL) ; |
| Monitor() ; |
| |
| public: |
| Monitor(int rank, const char *name, bool allow_vm_block = false, |
| SafepointCheckRequired safepoint_check_required = _safepoint_check_always); |
| ~Monitor(); |
| |
| // Wait until monitor is notified (or times out). |
| // Defaults are to make safepoint checks, wait time is forever (i.e., |
| // zero), and not a suspend-equivalent condition. Returns true if wait |
| // times out; otherwise returns false. |
| bool wait(bool no_safepoint_check = !_no_safepoint_check_flag, |
| long timeout = 0, |
| bool as_suspend_equivalent = !_as_suspend_equivalent_flag); |
| bool notify(); |
| bool notify_all(); |
| |
| |
| void lock(); // prints out warning if VM thread blocks |
| void lock(Thread *thread); // overloaded with current thread |
| void unlock(); |
| bool is_locked() const { return _owner != NULL; } |
| |
| bool try_lock(); // Like lock(), but unblocking. It returns false instead |
| |
| // Lock without safepoint check. Should ONLY be used by safepoint code and other code |
| // that is guaranteed not to block while running inside the VM. |
| void lock_without_safepoint_check(); |
| void lock_without_safepoint_check (Thread * Self) ; |
| |
| // Current owner - not not MT-safe. Can only be used to guarantee that |
| // the current running thread owns the lock |
| Thread* owner() const { return _owner; } |
| bool owned_by_self() const; |
| |
| // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by |
| // non-Java thread. (We should really have a RawMonitor abstraction) |
| void jvm_raw_lock(); |
| void jvm_raw_unlock(); |
| const char *name() const { return _name; } |
| |
| void print_on_error(outputStream* st) const; |
| |
| #ifndef PRODUCT |
| void print_on(outputStream* st) const; |
| void print() const { print_on(tty); } |
| debug_only(int rank() const { return _rank; }) |
| bool allow_vm_block() { return _allow_vm_block; } |
| |
| debug_only(Monitor *next() const { return _next; }) |
| debug_only(void set_next(Monitor *next) { _next = next; }) |
| #endif |
| |
| void set_owner(Thread* owner) { |
| #ifndef PRODUCT |
| set_owner_implementation(owner); |
| debug_only(void verify_Monitor(Thread* thr)); |
| #else |
| _owner = owner; |
| #endif |
| } |
| |
| }; |
| |
| class PaddedMonitor : public Monitor { |
| enum { |
| CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Monitor), |
| PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1 |
| }; |
| char _padding[PADDING_LEN]; |
| public: |
| PaddedMonitor(int rank, const char *name, bool allow_vm_block = false, |
| SafepointCheckRequired safepoint_check_required = _safepoint_check_always) : |
| Monitor(rank, name, allow_vm_block, safepoint_check_required) {}; |
| }; |
| |
| // Normally we'd expect Monitor to extend Mutex in the sense that a monitor |
| // constructed from pthreads primitives might extend a mutex by adding |
| // a condvar and some extra metadata. In fact this was the case until J2SE7. |
| // |
| // Currently, however, the base object is a monitor. Monitor contains all the |
| // logic for wait(), notify(), etc. Mutex extends monitor and restricts the |
| // visibility of wait(), notify(), and notify_all(). |
| // |
| // Another viable alternative would have been to have Monitor extend Mutex and |
| // implement all the normal mutex and wait()-notify() logic in Mutex base class. |
| // The wait()-notify() facility would be exposed via special protected member functions |
| // (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait() |
| // as a call to _Wait(). That is, the public wait() would be a wrapper for the protected |
| // _Wait(). |
| // |
| // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead. |
| // After all, monitors are sufficient for Java-level synchronization. At one point in time |
| // there may have been some benefit to having distinct mutexes and monitors, but that time |
| // has past. |
| // |
| // The Mutex/Monitor design parallels that of Java-monitors, being based on |
| // thread-specific park-unpark platform-specific primitives. |
| |
| |
| class Mutex : public Monitor { // degenerate Monitor |
| public: |
| Mutex(int rank, const char *name, bool allow_vm_block = false, |
| SafepointCheckRequired safepoint_check_required = _safepoint_check_always); |
| // default destructor |
| private: |
| bool notify () { ShouldNotReachHere(); return false; } |
| bool notify_all() { ShouldNotReachHere(); return false; } |
| bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) { |
| ShouldNotReachHere() ; |
| return false ; |
| } |
| }; |
| |
| class PaddedMutex : public Mutex { |
| enum { |
| CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Mutex), |
| PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1 |
| }; |
| char _padding[PADDING_LEN]; |
| public: |
| PaddedMutex(int rank, const char *name, bool allow_vm_block = false, |
| SafepointCheckRequired safepoint_check_required = _safepoint_check_always) : |
| Mutex(rank, name, allow_vm_block, safepoint_check_required) {}; |
| }; |
| |
| #endif // SHARE_VM_RUNTIME_MUTEX_HPP |