6988353: refactor contended sync subsystem

Reduce complexity by factoring synchronizer.cpp

Reviewed-by: dholmes, never, coleenp

hotspot/src/share/vm/runtime/park.cpp

@@ -0,0 +1,237 @@
+/*
+ * Copyright (c) 1997, 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.
+ *
+ */
+
+
+# include "incls/_precompiled.incl"
+# include "incls/_park.cpp.incl"
+
+
+// Lifecycle management for TSM ParkEvents.
+// ParkEvents are type-stable (TSM).
+// In our particular implementation they happen to be immortal.
+//
+// We manage concurrency on the FreeList with a CAS-based
+// detach-modify-reattach idiom that avoids the ABA problems
+// that would otherwise be present in a simple CAS-based
+// push-pop implementation.   (push-one and pop-all)
+//
+// Caveat: Allocate() and Release() may be called from threads
+// other than the thread associated with the Event!
+// If we need to call Allocate() when running as the thread in
+// question then look for the PD calls to initialize native TLS.
+// Native TLS (Win32/Linux/Solaris) can only be initialized or
+// accessed by the associated thread.
+// See also pd_initialize().
+//
+// Note that we could defer associating a ParkEvent with a thread
+// until the 1st time the thread calls park().  unpark() calls to
+// an unprovisioned thread would be ignored.  The first park() call
+// for a thread would allocate and associate a ParkEvent and return
+// immediately.
+
+volatile int ParkEvent::ListLock = 0 ;
+ParkEvent * volatile ParkEvent::FreeList = NULL ;
+
+ParkEvent * ParkEvent::Allocate (Thread * t) {
+  // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
+  ParkEvent * ev ;
+
+  // Start by trying to recycle an existing but unassociated
+  // ParkEvent from the global free list.
+  for (;;) {
+    ev = FreeList ;
+    if (ev == NULL) break ;
+    // 1: Detach - sequester or privatize the list
+    // Tantamount to ev = Swap (&FreeList, NULL)
+    if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
+       continue ;
+    }
+
+    // We've detached the list.  The list in-hand is now
+    // local to this thread.   This thread can operate on the
+    // list without risk of interference from other threads.
+    // 2: Extract -- pop the 1st element from the list.
+    ParkEvent * List = ev->FreeNext ;
+    if (List == NULL) break ;
+    for (;;) {
+        // 3: Try to reattach the residual list
+        guarantee (List != NULL, "invariant") ;
+        ParkEvent * Arv =  (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
+        if (Arv == NULL) break ;
+
+        // New nodes arrived.  Try to detach the recent arrivals.
+        if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
+            continue ;
+        }
+        guarantee (Arv != NULL, "invariant") ;
+        // 4: Merge Arv into List
+        ParkEvent * Tail = List ;
+        while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
+        Tail->FreeNext = Arv ;
+    }
+    break ;
+  }
+
+  if (ev != NULL) {
+    guarantee (ev->AssociatedWith == NULL, "invariant") ;
+  } else {
+    // Do this the hard way -- materialize a new ParkEvent.
+    // In rare cases an allocating thread might detach a long list --
+    // installing null into FreeList -- and then stall or be obstructed.
+    // A 2nd thread calling Allocate() would see FreeList == null.
+    // The list held privately by the 1st thread is unavailable to the 2nd thread.
+    // In that case the 2nd thread would have to materialize a new ParkEvent,
+    // even though free ParkEvents existed in the system.  In this case we end up
+    // with more ParkEvents in circulation than we need, but the race is
+    // rare and the outcome is benign.  Ideally, the # of extant ParkEvents
+    // is equal to the maximum # of threads that existed at any one time.
+    // Because of the race mentioned above, segments of the freelist
+    // can be transiently inaccessible.  At worst we may end up with the
+    // # of ParkEvents in circulation slightly above the ideal.
+    // Note that if we didn't have the TSM/immortal constraint, then
+    // when reattaching, above, we could trim the list.
+    ev = new ParkEvent () ;
+    guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
+  }
+  ev->reset() ;                     // courtesy to caller
+  ev->AssociatedWith = t ;          // Associate ev with t
+  ev->FreeNext       = NULL ;
+  return ev ;
+}
+
+void ParkEvent::Release (ParkEvent * ev) {
+  if (ev == NULL) return ;
+  guarantee (ev->FreeNext == NULL      , "invariant") ;
+  ev->AssociatedWith = NULL ;
+  for (;;) {
+    // Push ev onto FreeList
+    // The mechanism is "half" lock-free.
+    ParkEvent * List = FreeList ;
+    ev->FreeNext = List ;
+    if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
+  }
+}
+
+// Override operator new and delete so we can ensure that the
+// least significant byte of ParkEvent addresses is 0.
+// Beware that excessive address alignment is undesirable
+// as it can result in D$ index usage imbalance as
+// well as bank access imbalance on Niagara-like platforms,
+// although Niagara's hash function should help.
+
+void * ParkEvent::operator new (size_t sz) {
+  return (void *) ((intptr_t (CHeapObj::operator new (sz + 256)) + 256) & -256) ;
+}
+
+void ParkEvent::operator delete (void * a) {
+  // ParkEvents are type-stable and immortal ...
+  ShouldNotReachHere();
+}
+
+
+// 6399321 As a temporary measure we copied & modified the ParkEvent::
+// allocate() and release() code for use by Parkers.  The Parker:: forms
+// will eventually be removed as we consolide and shift over to ParkEvents
+// for both builtin synchronization and JSR166 operations.
+
+volatile int Parker::ListLock = 0 ;
+Parker * volatile Parker::FreeList = NULL ;
+
+Parker * Parker::Allocate (JavaThread * t) {
+  guarantee (t != NULL, "invariant") ;
+  Parker * p ;
+
+  // Start by trying to recycle an existing but unassociated
+  // Parker from the global free list.
+  for (;;) {
+    p = FreeList ;
+    if (p  == NULL) break ;
+    // 1: Detach
+    // Tantamount to p = Swap (&FreeList, NULL)
+    if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
+       continue ;
+    }
+
+    // We've detached the list.  The list in-hand is now
+    // local to this thread.   This thread can operate on the
+    // list without risk of interference from other threads.
+    // 2: Extract -- pop the 1st element from the list.
+    Parker * List = p->FreeNext ;
+    if (List == NULL) break ;
+    for (;;) {
+        // 3: Try to reattach the residual list
+        guarantee (List != NULL, "invariant") ;
+        Parker * Arv =  (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
+        if (Arv == NULL) break ;
+
+        // New nodes arrived.  Try to detach the recent arrivals.
+        if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
+            continue ;
+        }
+        guarantee (Arv != NULL, "invariant") ;
+        // 4: Merge Arv into List
+        Parker * Tail = List ;
+        while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
+        Tail->FreeNext = Arv ;
+    }
+    break ;
+  }
+
+  if (p != NULL) {
+    guarantee (p->AssociatedWith == NULL, "invariant") ;
+  } else {
+    // Do this the hard way -- materialize a new Parker..
+    // In rare cases an allocating thread might detach
+    // a long list -- installing null into FreeList --and
+    // then stall.  Another thread calling Allocate() would see
+    // FreeList == null and then invoke the ctor.  In this case we
+    // end up with more Parkers in circulation than we need, but
+    // the race is rare and the outcome is benign.
+    // Ideally, the # of extant Parkers is equal to the
+    // maximum # of threads that existed at any one time.
+    // Because of the race mentioned above, segments of the
+    // freelist can be transiently inaccessible.  At worst
+    // we may end up with the # of Parkers in circulation
+    // slightly above the ideal.
+    p = new Parker() ;
+  }
+  p->AssociatedWith = t ;          // Associate p with t
+  p->FreeNext       = NULL ;
+  return p ;
+}
+
+
+void Parker::Release (Parker * p) {
+  if (p == NULL) return ;
+  guarantee (p->AssociatedWith != NULL, "invariant") ;
+  guarantee (p->FreeNext == NULL      , "invariant") ;
+  p->AssociatedWith = NULL ;
+  for (;;) {
+    // Push p onto FreeList
+    Parker * List = FreeList ;
+    p->FreeNext = List ;
+    if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
+  }
+}
+