8006fe8f75
Replaced MakeDeps and the includeDB files with more standardized solutions. Reviewed-by: coleenp, kvn, kamg
238 lines
8.8 KiB
C++
238 lines
8.8 KiB
C++
/*
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* Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "runtime/thread.hpp"
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// Lifecycle management for TSM ParkEvents.
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// ParkEvents are type-stable (TSM).
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// In our particular implementation they happen to be immortal.
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//
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// We manage concurrency on the FreeList with a CAS-based
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// detach-modify-reattach idiom that avoids the ABA problems
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// that would otherwise be present in a simple CAS-based
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// push-pop implementation. (push-one and pop-all)
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//
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// Caveat: Allocate() and Release() may be called from threads
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// other than the thread associated with the Event!
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// If we need to call Allocate() when running as the thread in
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// question then look for the PD calls to initialize native TLS.
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// Native TLS (Win32/Linux/Solaris) can only be initialized or
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// accessed by the associated thread.
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// See also pd_initialize().
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//
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// Note that we could defer associating a ParkEvent with a thread
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// until the 1st time the thread calls park(). unpark() calls to
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// an unprovisioned thread would be ignored. The first park() call
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// for a thread would allocate and associate a ParkEvent and return
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// immediately.
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volatile int ParkEvent::ListLock = 0 ;
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ParkEvent * volatile ParkEvent::FreeList = NULL ;
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ParkEvent * ParkEvent::Allocate (Thread * t) {
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// In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
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ParkEvent * ev ;
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// Start by trying to recycle an existing but unassociated
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// ParkEvent from the global free list.
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for (;;) {
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ev = FreeList ;
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if (ev == NULL) break ;
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// 1: Detach - sequester or privatize the list
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// Tantamount to ev = Swap (&FreeList, NULL)
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if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
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continue ;
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}
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// We've detached the list. The list in-hand is now
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// local to this thread. This thread can operate on the
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// list without risk of interference from other threads.
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// 2: Extract -- pop the 1st element from the list.
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ParkEvent * List = ev->FreeNext ;
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if (List == NULL) break ;
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for (;;) {
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// 3: Try to reattach the residual list
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guarantee (List != NULL, "invariant") ;
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ParkEvent * Arv = (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
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if (Arv == NULL) break ;
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// New nodes arrived. Try to detach the recent arrivals.
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if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
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continue ;
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}
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guarantee (Arv != NULL, "invariant") ;
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// 4: Merge Arv into List
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ParkEvent * Tail = List ;
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while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
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Tail->FreeNext = Arv ;
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}
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break ;
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}
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if (ev != NULL) {
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guarantee (ev->AssociatedWith == NULL, "invariant") ;
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} else {
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// Do this the hard way -- materialize a new ParkEvent.
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// In rare cases an allocating thread might detach a long list --
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// installing null into FreeList -- and then stall or be obstructed.
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// A 2nd thread calling Allocate() would see FreeList == null.
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// The list held privately by the 1st thread is unavailable to the 2nd thread.
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// In that case the 2nd thread would have to materialize a new ParkEvent,
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// even though free ParkEvents existed in the system. In this case we end up
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// with more ParkEvents in circulation than we need, but the race is
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// rare and the outcome is benign. Ideally, the # of extant ParkEvents
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// is equal to the maximum # of threads that existed at any one time.
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// Because of the race mentioned above, segments of the freelist
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// can be transiently inaccessible. At worst we may end up with the
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// # of ParkEvents in circulation slightly above the ideal.
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// Note that if we didn't have the TSM/immortal constraint, then
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// when reattaching, above, we could trim the list.
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ev = new ParkEvent () ;
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guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
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}
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ev->reset() ; // courtesy to caller
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ev->AssociatedWith = t ; // Associate ev with t
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ev->FreeNext = NULL ;
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return ev ;
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}
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void ParkEvent::Release (ParkEvent * ev) {
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if (ev == NULL) return ;
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guarantee (ev->FreeNext == NULL , "invariant") ;
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ev->AssociatedWith = NULL ;
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for (;;) {
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// Push ev onto FreeList
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// The mechanism is "half" lock-free.
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ParkEvent * List = FreeList ;
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ev->FreeNext = List ;
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if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
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}
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}
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// Override operator new and delete so we can ensure that the
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// least significant byte of ParkEvent addresses is 0.
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// Beware that excessive address alignment is undesirable
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// as it can result in D$ index usage imbalance as
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// well as bank access imbalance on Niagara-like platforms,
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// although Niagara's hash function should help.
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void * ParkEvent::operator new (size_t sz) {
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return (void *) ((intptr_t (CHeapObj::operator new (sz + 256)) + 256) & -256) ;
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}
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void ParkEvent::operator delete (void * a) {
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// ParkEvents are type-stable and immortal ...
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ShouldNotReachHere();
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}
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// 6399321 As a temporary measure we copied & modified the ParkEvent::
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// allocate() and release() code for use by Parkers. The Parker:: forms
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// will eventually be removed as we consolide and shift over to ParkEvents
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// for both builtin synchronization and JSR166 operations.
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volatile int Parker::ListLock = 0 ;
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Parker * volatile Parker::FreeList = NULL ;
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Parker * Parker::Allocate (JavaThread * t) {
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guarantee (t != NULL, "invariant") ;
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Parker * p ;
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// Start by trying to recycle an existing but unassociated
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// Parker from the global free list.
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for (;;) {
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p = FreeList ;
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if (p == NULL) break ;
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// 1: Detach
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// Tantamount to p = Swap (&FreeList, NULL)
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if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
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continue ;
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}
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// We've detached the list. The list in-hand is now
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// local to this thread. This thread can operate on the
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// list without risk of interference from other threads.
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// 2: Extract -- pop the 1st element from the list.
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Parker * List = p->FreeNext ;
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if (List == NULL) break ;
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for (;;) {
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// 3: Try to reattach the residual list
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guarantee (List != NULL, "invariant") ;
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Parker * Arv = (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
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if (Arv == NULL) break ;
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// New nodes arrived. Try to detach the recent arrivals.
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if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
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continue ;
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}
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guarantee (Arv != NULL, "invariant") ;
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// 4: Merge Arv into List
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Parker * Tail = List ;
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while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
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Tail->FreeNext = Arv ;
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}
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break ;
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}
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if (p != NULL) {
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guarantee (p->AssociatedWith == NULL, "invariant") ;
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} else {
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// Do this the hard way -- materialize a new Parker..
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// In rare cases an allocating thread might detach
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// a long list -- installing null into FreeList --and
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// then stall. Another thread calling Allocate() would see
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// FreeList == null and then invoke the ctor. In this case we
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// end up with more Parkers in circulation than we need, but
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// the race is rare and the outcome is benign.
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// Ideally, the # of extant Parkers is equal to the
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// maximum # of threads that existed at any one time.
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// Because of the race mentioned above, segments of the
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// freelist can be transiently inaccessible. At worst
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// we may end up with the # of Parkers in circulation
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// slightly above the ideal.
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p = new Parker() ;
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}
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p->AssociatedWith = t ; // Associate p with t
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p->FreeNext = NULL ;
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return p ;
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}
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void Parker::Release (Parker * p) {
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if (p == NULL) return ;
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guarantee (p->AssociatedWith != NULL, "invariant") ;
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guarantee (p->FreeNext == NULL , "invariant") ;
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p->AssociatedWith = NULL ;
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for (;;) {
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// Push p onto FreeList
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Parker * List = FreeList ;
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p->FreeNext = List ;
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if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
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}
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}
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