1.1 --- a/src/os/bsd/vm/os_bsd.cpp Tue Jan 22 05:55:04 2013 -0800
1.2 +++ b/src/os/bsd/vm/os_bsd.cpp Tue Jan 22 05:56:42 2013 -0800
1.3 @@ -1,5 +1,5 @@
1.4 /*
1.5 - * Copyright (c) 1999, 2012, Oracle and/or its affiliates. All rights reserved.
1.6 + * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
1.7 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.8 *
1.9 * This code is free software; you can redistribute it and/or modify it
1.10 @@ -4094,11 +4094,12 @@
1.11 }
1.12 -- _nParked ;
1.13
1.14 - // In theory we could move the ST of 0 into _Event past the unlock(),
1.15 - // but then we'd need a MEMBAR after the ST.
1.16 _Event = 0 ;
1.17 status = pthread_mutex_unlock(_mutex);
1.18 assert_status(status == 0, status, "mutex_unlock");
1.19 + // Paranoia to ensure our locked and lock-free paths interact
1.20 + // correctly with each other.
1.21 + OrderAccess::fence();
1.22 }
1.23 guarantee (_Event >= 0, "invariant") ;
1.24 }
1.25 @@ -4161,40 +4162,44 @@
1.26 status = pthread_mutex_unlock(_mutex);
1.27 assert_status(status == 0, status, "mutex_unlock");
1.28 assert (_nParked == 0, "invariant") ;
1.29 + // Paranoia to ensure our locked and lock-free paths interact
1.30 + // correctly with each other.
1.31 + OrderAccess::fence();
1.32 return ret;
1.33 }
1.34
1.35 void os::PlatformEvent::unpark() {
1.36 - int v, AnyWaiters ;
1.37 - for (;;) {
1.38 - v = _Event ;
1.39 - if (v > 0) {
1.40 - // The LD of _Event could have reordered or be satisfied
1.41 - // by a read-aside from this processor's write buffer.
1.42 - // To avoid problems execute a barrier and then
1.43 - // ratify the value.
1.44 - OrderAccess::fence() ;
1.45 - if (_Event == v) return ;
1.46 - continue ;
1.47 - }
1.48 - if (Atomic::cmpxchg (v+1, &_Event, v) == v) break ;
1.49 + // Transitions for _Event:
1.50 + // 0 :=> 1
1.51 + // 1 :=> 1
1.52 + // -1 :=> either 0 or 1; must signal target thread
1.53 + // That is, we can safely transition _Event from -1 to either
1.54 + // 0 or 1. Forcing 1 is slightly more efficient for back-to-back
1.55 + // unpark() calls.
1.56 + // See also: "Semaphores in Plan 9" by Mullender & Cox
1.57 + //
1.58 + // Note: Forcing a transition from "-1" to "1" on an unpark() means
1.59 + // that it will take two back-to-back park() calls for the owning
1.60 + // thread to block. This has the benefit of forcing a spurious return
1.61 + // from the first park() call after an unpark() call which will help
1.62 + // shake out uses of park() and unpark() without condition variables.
1.63 +
1.64 + if (Atomic::xchg(1, &_Event) >= 0) return;
1.65 +
1.66 + // Wait for the thread associated with the event to vacate
1.67 + int status = pthread_mutex_lock(_mutex);
1.68 + assert_status(status == 0, status, "mutex_lock");
1.69 + int AnyWaiters = _nParked;
1.70 + assert(AnyWaiters == 0 || AnyWaiters == 1, "invariant");
1.71 + if (AnyWaiters != 0 && WorkAroundNPTLTimedWaitHang) {
1.72 + AnyWaiters = 0;
1.73 + pthread_cond_signal(_cond);
1.74 }
1.75 - if (v < 0) {
1.76 - // Wait for the thread associated with the event to vacate
1.77 - int status = pthread_mutex_lock(_mutex);
1.78 - assert_status(status == 0, status, "mutex_lock");
1.79 - AnyWaiters = _nParked ;
1.80 - assert (AnyWaiters == 0 || AnyWaiters == 1, "invariant") ;
1.81 - if (AnyWaiters != 0 && WorkAroundNPTLTimedWaitHang) {
1.82 - AnyWaiters = 0 ;
1.83 - pthread_cond_signal (_cond);
1.84 - }
1.85 - status = pthread_mutex_unlock(_mutex);
1.86 - assert_status(status == 0, status, "mutex_unlock");
1.87 - if (AnyWaiters != 0) {
1.88 - status = pthread_cond_signal(_cond);
1.89 - assert_status(status == 0, status, "cond_signal");
1.90 - }
1.91 + status = pthread_mutex_unlock(_mutex);
1.92 + assert_status(status == 0, status, "mutex_unlock");
1.93 + if (AnyWaiters != 0) {
1.94 + status = pthread_cond_signal(_cond);
1.95 + assert_status(status == 0, status, "cond_signal");
1.96 }
1.97
1.98 // Note that we signal() _after dropping the lock for "immortal" Events.
1.99 @@ -4280,13 +4285,14 @@
1.100 }
1.101
1.102 void Parker::park(bool isAbsolute, jlong time) {
1.103 + // Ideally we'd do something useful while spinning, such
1.104 + // as calling unpackTime().
1.105 +
1.106 // Optional fast-path check:
1.107 // Return immediately if a permit is available.
1.108 - if (_counter > 0) {
1.109 - _counter = 0 ;
1.110 - OrderAccess::fence();
1.111 - return ;
1.112 - }
1.113 + // We depend on Atomic::xchg() having full barrier semantics
1.114 + // since we are doing a lock-free update to _counter.
1.115 + if (Atomic::xchg(0, &_counter) > 0) return;
1.116
1.117 Thread* thread = Thread::current();
1.118 assert(thread->is_Java_thread(), "Must be JavaThread");
1.119 @@ -4327,6 +4333,8 @@
1.120 _counter = 0;
1.121 status = pthread_mutex_unlock(_mutex);
1.122 assert (status == 0, "invariant") ;
1.123 + // Paranoia to ensure our locked and lock-free paths interact
1.124 + // correctly with each other and Java-level accesses.
1.125 OrderAccess::fence();
1.126 return;
1.127 }
1.128 @@ -4363,12 +4371,14 @@
1.129 _counter = 0 ;
1.130 status = pthread_mutex_unlock(_mutex) ;
1.131 assert_status(status == 0, status, "invariant") ;
1.132 + // Paranoia to ensure our locked and lock-free paths interact
1.133 + // correctly with each other and Java-level accesses.
1.134 + OrderAccess::fence();
1.135 +
1.136 // If externally suspended while waiting, re-suspend
1.137 if (jt->handle_special_suspend_equivalent_condition()) {
1.138 jt->java_suspend_self();
1.139 }
1.140 -
1.141 - OrderAccess::fence();
1.142 }
1.143
1.144 void Parker::unpark() {
