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8004902: correctness fixes motivated by contended locking work (6607129)

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Misc correctness fixes

Reviewed-by: acorn, dholmes, dice, sspitsyn
This commit is contained in:
Dave Dice 2013-01-22 05:56:42 -08:00 • committed by Daniel D. Daugherty
parent 8f1dc20874
commit 98c357abf8
7 changed files with 168 additions and 152 deletions
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88
hotspot/src/os/linux/vm/os_linux.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1999, 2012, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1999, 2013, 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
@ -5001,11 +5001,12 @@ void os::PlatformEvent::park() { // AKA "down()"
}
-- _nParked ;
// In theory we could move the ST of 0 into _Event past the unlock(),
// but then we'd need a MEMBAR after the ST.
_Event = 0 ;
status = pthread_mutex_unlock(_mutex);
assert_status(status == 0, status, "mutex_unlock");
// Paranoia to ensure our locked and lock-free paths interact
// correctly with each other.
OrderAccess::fence();
}
guarantee (_Event >= 0, "invariant") ;
}
@ -5068,40 +5069,44 @@ int os::PlatformEvent::park(jlong millis) {
status = pthread_mutex_unlock(_mutex);
assert_status(status == 0, status, "mutex_unlock");
assert (_nParked == 0, "invariant") ;
// Paranoia to ensure our locked and lock-free paths interact
// correctly with each other.
OrderAccess::fence();
return ret;
}
void os::PlatformEvent::unpark() {
int v, AnyWaiters ;
for (;;) {
v = _Event ;
if (v > 0) {
// The LD of _Event could have reordered or be satisfied
// by a read-aside from this processor's write buffer.
// To avoid problems execute a barrier and then
// ratify the value.
OrderAccess::fence() ;
if (_Event == v) return ;
continue ;
}
if (Atomic::cmpxchg (v+1, &_Event, v) == v) break ;
// Transitions for _Event:
// 0 :=> 1
// 1 :=> 1
// -1 :=> either 0 or 1; must signal target thread
// That is, we can safely transition _Event from -1 to either
// 0 or 1. Forcing 1 is slightly more efficient for back-to-back
// unpark() calls.
// See also: "Semaphores in Plan 9" by Mullender & Cox
//
// Note: Forcing a transition from "-1" to "1" on an unpark() means
// that it will take two back-to-back park() calls for the owning
// thread to block. This has the benefit of forcing a spurious return
// from the first park() call after an unpark() call which will help
// shake out uses of park() and unpark() without condition variables.
if (Atomic::xchg(1, &_Event) >= 0) return;
// Wait for the thread associated with the event to vacate
int status = pthread_mutex_lock(_mutex);
assert_status(status == 0, status, "mutex_lock");
int AnyWaiters = _nParked;
assert(AnyWaiters == 0 || AnyWaiters == 1, "invariant");
if (AnyWaiters != 0 && WorkAroundNPTLTimedWaitHang) {
AnyWaiters = 0;
pthread_cond_signal(_cond);
}
if (v < 0) {
// Wait for the thread associated with the event to vacate
int status = pthread_mutex_lock(_mutex);
assert_status(status == 0, status, "mutex_lock");
AnyWaiters = _nParked ;
assert (AnyWaiters == 0 || AnyWaiters == 1, "invariant") ;
if (AnyWaiters != 0 && WorkAroundNPTLTimedWaitHang) {
AnyWaiters = 0 ;
pthread_cond_signal (_cond);
}
status = pthread_mutex_unlock(_mutex);
assert_status(status == 0, status, "mutex_unlock");
if (AnyWaiters != 0) {
status = pthread_cond_signal(_cond);
assert_status(status == 0, status, "cond_signal");
}
status = pthread_mutex_unlock(_mutex);
assert_status(status == 0, status, "mutex_unlock");
if (AnyWaiters != 0) {
status = pthread_cond_signal(_cond);
assert_status(status == 0, status, "cond_signal");
}
// Note that we signal() _after dropping the lock for "immortal" Events.
@ -5187,13 +5192,14 @@ static void unpackTime(timespec* absTime, bool isAbsolute, jlong time) {
}
void Parker::park(bool isAbsolute, jlong time) {
// Ideally we'd do something useful while spinning, such
// as calling unpackTime().
// Optional fast-path check:
// Return immediately if a permit is available.
if (_counter > 0) {
_counter = 0 ;
OrderAccess::fence();
return ;
}
// We depend on Atomic::xchg() having full barrier semantics
// since we are doing a lock-free update to _counter.
if (Atomic::xchg(0, &_counter) > 0) return;
Thread* thread = Thread::current();
assert(thread->is_Java_thread(), "Must be JavaThread");
@ -5234,6 +5240,8 @@ void Parker::park(bool isAbsolute, jlong time) {
_counter = 0;
status = pthread_mutex_unlock(_mutex);
assert (status == 0, "invariant") ;
// Paranoia to ensure our locked and lock-free paths interact
// correctly with each other and Java-level accesses.
OrderAccess::fence();
return;
}
@ -5270,12 +5278,14 @@ void Parker::park(bool isAbsolute, jlong time) {
_counter = 0 ;
status = pthread_mutex_unlock(_mutex) ;
assert_status(status == 0, status, "invariant") ;
// Paranoia to ensure our locked and lock-free paths interact
// correctly with each other and Java-level accesses.
OrderAccess::fence();
// If externally suspended while waiting, re-suspend
if (jt->handle_special_suspend_equivalent_condition()) {
jt->java_suspend_self();
}
OrderAccess::fence();
}
void Parker::unpark() {