src/hotspot/share/runtime/mutex.hpp - platform/libcore - Git at Google

 /*
  * Copyright (c) 1998, 2019, 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_RUNTIME_MUTEX_HPP
 #define SHARE_RUNTIME_MUTEX_HPP

 #include "memory/allocation.hpp"
 #include "runtime/os.hpp"

 // A Mutex/Monitor is a simple wrapper around a native lock plus condition
 // variable that supports lock ownership tracking, lock ranking for deadlock
 // detection and coordinates with the safepoint protocol.

 // 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<mtSynchronizer> {

  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.
   // The rank 'tty' is also similar to 'special' and has the same restrictions.
   // It is reserved for the tty_lock.
   // 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.
   // 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,
        tty            = access         +   2,
        special        = tty            +   1,
        suspend_resume = special        +   1,
        vmweak         = suspend_resume +   2,
        leaf           = vmweak         +   2,
        safepoint      = leaf           +  10,
        barrier        = safepoint      +   1,
        nonleaf        = barrier        +   1,
        max_nonleaf    = nonleaf        + 900,
        native         = max_nonleaf    +   1
   };

  protected:                              // Monitor-Mutex metadata
   Thread * volatile _owner;              // The owner of the lock
   os::PlatformMonitor _lock;             // Native monitor implementation
   char _name[MONITOR_NAME_LEN];          // Name of mutex/monitor

   // 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, bool safepoint_check) PRODUCT_RETURN;
   void check_block_state       (Thread* thread)                       PRODUCT_RETURN;
   void check_safepoint_state   (Thread* thread, bool safepoint_check) NOT_DEBUG_RETURN;
   void assert_owner            (Thread* expected)                     NOT_DEBUG_RETURN;
   void assert_wait_lock_state  (Thread* self)                         NOT_DEBUG_RETURN;

  public:
   enum {
     _allow_vm_block_flag        = true,
     _as_suspend_equivalent_flag = true
   };

   // Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
   // the safepoint protocol when acquiring locks.

   // Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
   // Java and NonJavaThreads. When the lock is initialized with _safepoint_check_always,
   // that means that whenever the lock is acquired by a JavaThread, it will verify that
   // it is done with a safepoint check. In corollary, when the lock is initialized with
   // _safepoint_check_never, that means that whenever the lock is acquired by a JavaThread
   // it will verify that it is done without a safepoint check.


   // There are a couple of existing locks that will sometimes have a safepoint check and
   // sometimes not when acquired by a JavaThread, but these locks are set up carefully
   // to avoid deadlocks. TODO: Fix these locks and remove _safepoint_check_sometimes.

   // TODO: Locks that are shared between JavaThreads and NonJavaThreads
   // should never encounter a safepoint check while they are held, or else a
   // deadlock can occur. We should check this by noting which
   // locks are shared, and walk held locks during safepoint checking.

   enum SafepointCheckFlag {
     _safepoint_check_flag,
     _no_safepoint_check_flag
   };

   enum SafepointCheckRequired {
     _safepoint_check_never,       // Monitors with this value will cause errors
                                   // when acquired by a JavaThread with a safepoint check.
     _safepoint_check_sometimes,   // A couple of special locks are acquired by JavaThreads sometimes
                                   // with and sometimes without safepoint checks. These
                                   // locks will not produce errors when locked.
     _safepoint_check_always       // Monitors with this value will cause errors
                                   // when acquired by a JavaThread without a safepoint check.
   };

   NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;)

  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(long timeout = 0,
             bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
   bool wait_without_safepoint_check(long timeout = 0);
   void notify();
   void 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

   void release_for_safepoint();

   // 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 passed.
 //

 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:
    void notify();
    void notify_all();
    bool wait(long timeout, bool as_suspend_equivalent);
    bool wait_without_safepoint_check(long timeout);
 };

 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_RUNTIME_MUTEX_HPP
	/*
	* Copyright (c) 1998, 2019, 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_RUNTIME_MUTEX_HPP
	#define SHARE_RUNTIME_MUTEX_HPP

	#include "memory/allocation.hpp"
	#include "runtime/os.hpp"

	// A Mutex/Monitor is a simple wrapper around a native lock plus condition
	// variable that supports lock ownership tracking, lock ranking for deadlock
	// detection and coordinates with the safepoint protocol.

	// 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<mtSynchronizer> {

	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.
	// The rank 'tty' is also similar to 'special' and has the same restrictions.
	// It is reserved for the tty_lock.
	// 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.
	// 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,
	tty = access + 2,
	special = tty + 1,
	suspend_resume = special + 1,
	vmweak = suspend_resume + 2,
	leaf = vmweak + 2,
	safepoint = leaf + 10,
	barrier = safepoint + 1,
	nonleaf = barrier + 1,
	max_nonleaf = nonleaf + 900,
	native = max_nonleaf + 1
	};

	protected: // Monitor-Mutex metadata
	Thread * volatile _owner; // The owner of the lock
	os::PlatformMonitor _lock; // Native monitor implementation
	char _name[MONITOR_NAME_LEN]; // Name of mutex/monitor

	// 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, bool safepoint_check) PRODUCT_RETURN;
	void check_block_state (Thread* thread) PRODUCT_RETURN;
	void check_safepoint_state (Thread* thread, bool safepoint_check) NOT_DEBUG_RETURN;
	void assert_owner (Thread* expected) NOT_DEBUG_RETURN;
	void assert_wait_lock_state (Thread* self) NOT_DEBUG_RETURN;

	public:
	enum {
	_allow_vm_block_flag = true,
	_as_suspend_equivalent_flag = true
	};

	// Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
	// the safepoint protocol when acquiring locks.

	// Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
	// Java and NonJavaThreads. When the lock is initialized with _safepoint_check_always,
	// that means that whenever the lock is acquired by a JavaThread, it will verify that
	// it is done with a safepoint check. In corollary, when the lock is initialized with
	// _safepoint_check_never, that means that whenever the lock is acquired by a JavaThread
	// it will verify that it is done without a safepoint check.


	// There are a couple of existing locks that will sometimes have a safepoint check and
	// sometimes not when acquired by a JavaThread, but these locks are set up carefully
	// to avoid deadlocks. TODO: Fix these locks and remove _safepoint_check_sometimes.

	// TODO: Locks that are shared between JavaThreads and NonJavaThreads
	// should never encounter a safepoint check while they are held, or else a
	// deadlock can occur. We should check this by noting which
	// locks are shared, and walk held locks during safepoint checking.

	enum SafepointCheckFlag {
	_safepoint_check_flag,
	_no_safepoint_check_flag
	};

	enum SafepointCheckRequired {
	_safepoint_check_never, // Monitors with this value will cause errors
	// when acquired by a JavaThread with a safepoint check.
	_safepoint_check_sometimes, // A couple of special locks are acquired by JavaThreads sometimes
	// with and sometimes without safepoint checks. These
	// locks will not produce errors when locked.
	_safepoint_check_always // Monitors with this value will cause errors
	// when acquired by a JavaThread without a safepoint check.
	};

	NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;)

	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(long timeout = 0,
	bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
	bool wait_without_safepoint_check(long timeout = 0);
	void notify();
	void 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

	void release_for_safepoint();

	// 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 passed.
	//

	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:
	void notify();
	void notify_all();
	bool wait(long timeout, bool as_suspend_equivalent);
	bool wait_without_safepoint_check(long timeout);
	};

	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_RUNTIME_MUTEX_HPP