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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* published by the Free Software Foundation.
*
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* 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.
*
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#ifndef SHARE_RUNTIME_PARK_HPP
#define SHARE_RUNTIME_PARK_HPP
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#if defined(LINUX) || defined(AIX) || defined(BSD)
# include "park_posix.hpp"
#else
# include OS_HEADER(park)
#endif
class Thread;
/*
* Per-thread blocking support for JSR166. See the Java-level
* documentation for rationale. Basically, park acts like wait, unpark
* like notify.
*
* Parkers are inherently part of their associated JavaThread and are only
* accessed when the JavaThread is guaranteed to be alive (e.g. by operating
* on the current thread, or by having the thread protected by a
* ThreadsListHandle.
*
* Class Parker is declared in shared code and extends the platform-specific
* PlatformParker class, which contains the actual implementation
* mechanics (condvars/events etc). The implementation for park() and unpark()
* are also in the platform-specific os_<os>.cpp files.
*
* In the future we'll want to think about eliminating Parker and using
* ParkEvent instead. There's considerable duplication between the two
* services.
*
*/
class Parker : public PlatformParker {
private:
NONCOPYABLE(Parker);
public:
Parker() : PlatformParker() {}
// For simplicity of interface with Java, all forms of park (indefinite,
// relative, and absolute) are multiplexed into one call.
void park(bool isAbsolute, jlong time);
void unpark();
};
/////////////////////////////////////////////////////////////
//
// ParkEvents are type-stable and immortal.
//
// Lifecycle: Once a ParkEvent is associated with a thread that ParkEvent remains
// associated with the thread for the thread's entire lifetime - the relationship is
// stable. A thread will be associated at most one ParkEvent. When the thread
// expires, the ParkEvent moves to the EventFreeList. New threads attempt to allocate from
// the EventFreeList before creating a new Event. Type-stability frees us from
// worrying about stale Event or Thread references in the objectMonitor subsystem.
// (A reference to ParkEvent is always valid, even though the event may no longer be associated
// with the desired or expected thread. A key aspect of this design is that the callers of
// park, unpark, etc must tolerate stale references and spurious wakeups).
//
// Only the "associated" thread can block (park) on the ParkEvent, although
// any other thread can unpark a reachable parkevent. Park() is allowed to
// return spuriously. In fact park-unpark a really just an optimization to
// avoid unbounded spinning and surrender the CPU to be a polite system citizen.
// A degenerate albeit "impolite" park-unpark implementation could simply return.
// See http://blogs.sun.com/dave for more details.
//
// Eventually I'd like to eliminate Events and ObjectWaiters, both of which serve as
// thread proxies, and simply make the THREAD structure type-stable and persistent.
// Currently, we unpark events associated with threads, but ideally we'd just
// unpark threads.
//
// The base-class, PlatformEvent, is platform-specific while the ParkEvent is
// platform-independent. PlatformEvent provides park(), unpark(), etc., and
// is abstract -- that is, a PlatformEvent should never be instantiated except
// as part of a ParkEvent.
// Equivalently we could have defined a platform-independent base-class that
// exported Allocate(), Release(), etc. The platform-specific class would extend
// that base-class, adding park(), unpark(), etc.
//
// A word of caution: The JVM uses 2 very similar constructs:
// 1. ParkEvent are used for Java-level "monitor" synchronization.
// 2. Parkers are used by JSR166-JUC park-unpark.
//
// We'll want to eventually merge these redundant facilities and use ParkEvent.
class ParkEvent : public PlatformEvent {
private:
ParkEvent * FreeNext ;
// Current association
Thread * AssociatedWith ;
public:
// MCS-CLH list linkage and Native Mutex/Monitor
ParkEvent * volatile ListNext ;
volatile int TState ;
volatile int Notified ; // for native monitor construct
private:
static ParkEvent * volatile FreeList ;
static volatile int ListLock ;
// It's prudent to mark the dtor as "private"
// ensuring that it's not visible outside the package.
// Unfortunately gcc warns about such usage, so
// we revert to the less desirable "protected" visibility.
// The other compilers accept private dtors.
protected: // Ensure dtor is never invoked
~ParkEvent() { guarantee (0, "invariant") ; }
ParkEvent() : PlatformEvent() {
AssociatedWith = NULL ;
FreeNext = NULL ;
ListNext = NULL ;
TState = 0 ;
Notified = 0 ;
}
// We use placement-new to force ParkEvent instances to be
// aligned on 256-byte address boundaries. This ensures that the least
// significant byte of a ParkEvent address is always 0.
void * operator new (size_t sz) throw();
void operator delete (void * a) ;
public:
static ParkEvent * Allocate (Thread * t) ;
static void Release (ParkEvent * e) ;
} ;
#endif // SHARE_RUNTIME_PARK_HPP
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