Mercurial > hg > graal-compiler
view src/share/vm/runtime/mutex.hpp @ 6210:1e26f61bbb52 jdk8-b48
Added tag hs24-b16 for changeset 66b0450071c1
author | amurillo |
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date | Fri, 13 Jul 2012 14:06:34 -0700 |
parents | d2a62e0f25eb |
children | b9a9ed0f8eeb |
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/* * Copyright (c) 1998, 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. * */ #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 is chosen to be 64 to avoid false sharing. 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 locks, etc. // NOTE: It is critical that the rank 'special' be the lowest (earliest) // (except for "event"?) for the deadlock dection 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, special, suspend_resume, 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 }; 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); ~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 } }; // 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 // visiblity 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); ~Mutex () ; 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 ; } }; #endif // SHARE_VM_RUNTIME_MUTEX_HPP