1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/runtime/mutex.hpp Wed Apr 27 01:25:04 2016 +0800
1.3 @@ -0,0 +1,276 @@
1.4 +/*
1.5 + * Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.23 + * or visit www.oracle.com if you need additional information or have any
1.24 + * questions.
1.25 + *
1.26 + */
1.27 +
1.28 +#ifndef SHARE_VM_RUNTIME_MUTEX_HPP
1.29 +#define SHARE_VM_RUNTIME_MUTEX_HPP
1.30 +
1.31 +#include "memory/allocation.hpp"
1.32 +#include "runtime/os.hpp"
1.33 +#include "utilities/histogram.hpp"
1.34 +
1.35 +// The SplitWord construct allows us to colocate the contention queue
1.36 +// (cxq) with the lock-byte. The queue elements are ParkEvents, which are
1.37 +// always aligned on 256-byte addresses - the least significant byte of
1.38 +// a ParkEvent is always 0. Colocating the lock-byte with the queue
1.39 +// allows us to easily avoid what would otherwise be a race in lock()
1.40 +// if we were to use two completely separate fields for the contention queue
1.41 +// and the lock indicator. Specifically, colocation renders us immune
1.42 +// from the race where a thread might enqueue itself in the lock() slow-path
1.43 +// immediately after the lock holder drops the outer lock in the unlock()
1.44 +// fast-path.
1.45 +//
1.46 +// Colocation allows us to use a fast-path unlock() form that uses
1.47 +// A MEMBAR instead of a CAS. MEMBAR has lower local latency than CAS
1.48 +// on many platforms.
1.49 +//
1.50 +// See:
1.51 +// + http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
1.52 +// + http://blogs.sun.com/dave/resource/synchronization-public2.pdf
1.53 +//
1.54 +// Note that we're *not* using word-tearing the classic sense.
1.55 +// The lock() fast-path will CAS the lockword and the unlock()
1.56 +// fast-path will store into the lock-byte colocated within the lockword.
1.57 +// We depend on the fact that all our reference platforms have
1.58 +// coherent and atomic byte accesses. More precisely, byte stores
1.59 +// interoperate in a safe, sane, and expected manner with respect to
1.60 +// CAS, ST and LDs to the full-word containing the byte.
1.61 +// If you're porting HotSpot to a platform where that isn't the case
1.62 +// then you'll want change the unlock() fast path from:
1.63 +// STB;MEMBAR #storeload; LDN
1.64 +// to a full-word CAS of the lockword.
1.65 +
1.66 +
1.67 +union SplitWord { // full-word with separately addressable LSB
1.68 + volatile intptr_t FullWord ;
1.69 + volatile void * Address ;
1.70 + volatile jbyte Bytes [sizeof(intptr_t)] ;
1.71 +} ;
1.72 +
1.73 +// Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
1.74 +#ifdef VM_LITTLE_ENDIAN
1.75 + #define _LSBINDEX 0
1.76 +#else
1.77 + #define _LSBINDEX (sizeof(intptr_t)-1)
1.78 +#endif
1.79 +
1.80 +class ParkEvent ;
1.81 +
1.82 +// See orderAccess.hpp. We assume throughout the VM that mutex lock and
1.83 +// try_lock do fence-lock-acquire, and that unlock does a release-unlock,
1.84 +// *in that order*. If their implementations change such that these
1.85 +// assumptions are violated, a whole lot of code will break.
1.86 +
1.87 +// The default length of monitor name is chosen to be 64 to avoid false sharing.
1.88 +static const int MONITOR_NAME_LEN = 64;
1.89 +
1.90 +class Monitor : public CHeapObj<mtInternal> {
1.91 +
1.92 + public:
1.93 + // A special lock: Is a lock where you are guaranteed not to block while you are
1.94 + // holding it, i.e., no vm operation can happen, taking other locks, etc.
1.95 + // NOTE: It is critical that the rank 'special' be the lowest (earliest)
1.96 + // (except for "event"?) for the deadlock dection to work correctly.
1.97 + // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
1.98 + // which being external to the VM are not subject to deadlock detection.
1.99 + // The rank safepoint is used only for synchronization in reaching a
1.100 + // safepoint and leaving a safepoint. It is only used for the Safepoint_lock
1.101 + // currently. While at a safepoint no mutexes of rank safepoint are held
1.102 + // by any thread.
1.103 + // The rank named "leaf" is probably historical (and should
1.104 + // be changed) -- mutexes of this rank aren't really leaf mutexes
1.105 + // at all.
1.106 + enum lock_types {
1.107 + event,
1.108 + special,
1.109 + suspend_resume,
1.110 + leaf = suspend_resume + 2,
1.111 + safepoint = leaf + 10,
1.112 + barrier = safepoint + 1,
1.113 + nonleaf = barrier + 1,
1.114 + max_nonleaf = nonleaf + 900,
1.115 + native = max_nonleaf + 1
1.116 + };
1.117 +
1.118 + // The WaitSet and EntryList linked lists are composed of ParkEvents.
1.119 + // I use ParkEvent instead of threads as ParkEvents are immortal and
1.120 + // type-stable, meaning we can safely unpark() a possibly stale
1.121 + // list element in the unlock()-path.
1.122 +
1.123 + protected: // Monitor-Mutex metadata
1.124 + SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte
1.125 + enum LockWordBits { _LBIT=1 } ;
1.126 + Thread * volatile _owner; // The owner of the lock
1.127 + // Consider sequestering _owner on its own $line
1.128 + // to aid future synchronization mechanisms.
1.129 + ParkEvent * volatile _EntryList ; // List of threads waiting for entry
1.130 + ParkEvent * volatile _OnDeck ; // heir-presumptive
1.131 + volatile intptr_t _WaitLock [1] ; // Protects _WaitSet
1.132 + ParkEvent * volatile _WaitSet ; // LL of ParkEvents
1.133 + volatile bool _snuck; // Used for sneaky locking (evil).
1.134 + int NotifyCount ; // diagnostic assist
1.135 + char _name[MONITOR_NAME_LEN]; // Name of mutex
1.136 +
1.137 + // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
1.138 +#ifndef PRODUCT
1.139 + bool _allow_vm_block;
1.140 + debug_only(int _rank;) // rank (to avoid/detect potential deadlocks)
1.141 + debug_only(Monitor * _next;) // Used by a Thread to link up owned locks
1.142 + debug_only(Thread* _last_owner;) // the last thread to own the lock
1.143 + debug_only(static bool contains(Monitor * locks, Monitor * lock);)
1.144 + debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
1.145 + debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
1.146 +#endif
1.147 +
1.148 + void set_owner_implementation(Thread* owner) PRODUCT_RETURN;
1.149 + void check_prelock_state (Thread* thread) PRODUCT_RETURN;
1.150 + void check_block_state (Thread* thread) PRODUCT_RETURN;
1.151 +
1.152 + // platform-dependent support code can go here (in os_<os_family>.cpp)
1.153 + public:
1.154 + enum {
1.155 + _no_safepoint_check_flag = true,
1.156 + _allow_vm_block_flag = true,
1.157 + _as_suspend_equivalent_flag = true
1.158 + };
1.159 +
1.160 + enum WaitResults {
1.161 + CONDVAR_EVENT, // Wait returned because of condition variable notification
1.162 + INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted
1.163 + NUMBER_WAIT_RESULTS
1.164 + };
1.165 +
1.166 + private:
1.167 + int TrySpin (Thread * Self) ;
1.168 + int TryLock () ;
1.169 + int TryFast () ;
1.170 + int AcquireOrPush (ParkEvent * ev) ;
1.171 + void IUnlock (bool RelaxAssert) ;
1.172 + void ILock (Thread * Self) ;
1.173 + int IWait (Thread * Self, jlong timo);
1.174 + int ILocked () ;
1.175 +
1.176 + protected:
1.177 + static void ClearMonitor (Monitor * m, const char* name = NULL) ;
1.178 + Monitor() ;
1.179 +
1.180 + public:
1.181 + Monitor(int rank, const char *name, bool allow_vm_block=false);
1.182 + ~Monitor();
1.183 +
1.184 + // Wait until monitor is notified (or times out).
1.185 + // Defaults are to make safepoint checks, wait time is forever (i.e.,
1.186 + // zero), and not a suspend-equivalent condition. Returns true if wait
1.187 + // times out; otherwise returns false.
1.188 + bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
1.189 + long timeout = 0,
1.190 + bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
1.191 + bool notify();
1.192 + bool notify_all();
1.193 +
1.194 +
1.195 + void lock(); // prints out warning if VM thread blocks
1.196 + void lock(Thread *thread); // overloaded with current thread
1.197 + void unlock();
1.198 + bool is_locked() const { return _owner != NULL; }
1.199 +
1.200 + bool try_lock(); // Like lock(), but unblocking. It returns false instead
1.201 +
1.202 + // Lock without safepoint check. Should ONLY be used by safepoint code and other code
1.203 + // that is guaranteed not to block while running inside the VM.
1.204 + void lock_without_safepoint_check();
1.205 + void lock_without_safepoint_check (Thread * Self) ;
1.206 +
1.207 + // Current owner - not not MT-safe. Can only be used to guarantee that
1.208 + // the current running thread owns the lock
1.209 + Thread* owner() const { return _owner; }
1.210 + bool owned_by_self() const;
1.211 +
1.212 + // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
1.213 + // non-Java thread. (We should really have a RawMonitor abstraction)
1.214 + void jvm_raw_lock();
1.215 + void jvm_raw_unlock();
1.216 + const char *name() const { return _name; }
1.217 +
1.218 + void print_on_error(outputStream* st) const;
1.219 +
1.220 + #ifndef PRODUCT
1.221 + void print_on(outputStream* st) const;
1.222 + void print() const { print_on(tty); }
1.223 + debug_only(int rank() const { return _rank; })
1.224 + bool allow_vm_block() { return _allow_vm_block; }
1.225 +
1.226 + debug_only(Monitor *next() const { return _next; })
1.227 + debug_only(void set_next(Monitor *next) { _next = next; })
1.228 + #endif
1.229 +
1.230 + void set_owner(Thread* owner) {
1.231 + #ifndef PRODUCT
1.232 + set_owner_implementation(owner);
1.233 + debug_only(void verify_Monitor(Thread* thr));
1.234 + #else
1.235 + _owner = owner;
1.236 + #endif
1.237 + }
1.238 +
1.239 +};
1.240 +
1.241 +// Normally we'd expect Monitor to extend Mutex in the sense that a monitor
1.242 +// constructed from pthreads primitives might extend a mutex by adding
1.243 +// a condvar and some extra metadata. In fact this was the case until J2SE7.
1.244 +//
1.245 +// Currently, however, the base object is a monitor. Monitor contains all the
1.246 +// logic for wait(), notify(), etc. Mutex extends monitor and restricts the
1.247 +// visiblity of wait(), notify(), and notify_all().
1.248 +//
1.249 +// Another viable alternative would have been to have Monitor extend Mutex and
1.250 +// implement all the normal mutex and wait()-notify() logic in Mutex base class.
1.251 +// The wait()-notify() facility would be exposed via special protected member functions
1.252 +// (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait()
1.253 +// as a call to _Wait(). That is, the public wait() would be a wrapper for the protected
1.254 +// _Wait().
1.255 +//
1.256 +// An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
1.257 +// After all, monitors are sufficient for Java-level synchronization. At one point in time
1.258 +// there may have been some benefit to having distinct mutexes and monitors, but that time
1.259 +// has past.
1.260 +//
1.261 +// The Mutex/Monitor design parallels that of Java-monitors, being based on
1.262 +// thread-specific park-unpark platform-specific primitives.
1.263 +
1.264 +
1.265 +class Mutex : public Monitor { // degenerate Monitor
1.266 + public:
1.267 + Mutex (int rank, const char *name, bool allow_vm_block=false);
1.268 + ~Mutex () ;
1.269 + private:
1.270 + bool notify () { ShouldNotReachHere(); return false; }
1.271 + bool notify_all() { ShouldNotReachHere(); return false; }
1.272 + bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
1.273 + ShouldNotReachHere() ;
1.274 + return false ;
1.275 + }
1.276 +};
1.277 +
1.278 +
1.279 +#endif // SHARE_VM_RUNTIME_MUTEX_HPP
