Imported QtWebKit TP3 (git b57bc6801f1876c3220d5a4bfea33d620d477443)

Change-Id: I3b1d8a2808782c9f34d50240000e20cb38d3680f
Reviewed-by: Konstantin Tokarev <annulen@yandex.ru>

1 files changed, 251 insertions, 0 deletions

diff --git a/Source/WTF/wtf/Condition.h b/Source/WTF/wtf/Condition.h
new file mode 100644
index 000000000..80c07293a
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+++ b/Source/WTF/wtf/Condition.h
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+/*
+ * Copyright (C) 2015 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef WTF_Condition_h
+#define WTF_Condition_h
+
+#include <chrono>
+#include <functional>
+#include <wtf/CurrentTime.h>
+#include <wtf/Noncopyable.h>
+#include <wtf/ParkingLot.h>
+
+namespace WTF {
+
+// This is a condition variable that is suitable for use with any lock-like object, including
+// our own WTF::Lock. It features standard wait()/notifyOne()/notifyAll() methods in addition to
+// a variety of wait-with-timeout methods. This includes methods that use WTF's own notion of
+// time, like wall-clock time (i.e. currentTime()) and monotonic time (i.e.
+// monotonicallyIncreasingTime()). This is a very efficient condition variable. It only requires
+// one byte of memory. notifyOne() and notifyAll() require just a load and branch for the fast
+// case where no thread is waiting. This condition variable, when used with WTF::Lock, can
+// outperform a system condition variable and lock by up to 58x.
+
+// This is a struct without a constructor or destructor so that it can be statically initialized.
+// Use Lock in instance variables.
+struct ConditionBase {
+    typedef ParkingLot::Clock Clock;
+    
+    // Wait on a parking queue while releasing the given lock. It will unlock the lock just before
+    // parking, and relock it upon wakeup. Returns true if we woke up due to some call to
+    // notifyOne() or notifyAll(). Returns false if we woke up due to a timeout. Note that this form
+    // of waitUntil() has some quirks:
+    //
+    // No spurious wake-up: in order for this to return before the timeout, some notifyOne() or
+    // notifyAll() call must have happened. No scenario other than timeout or notify can lead to this
+    // method returning. This means, for example, that you can't use pthread cancelation or signals to
+    // cause early return.
+    //
+    // Past timeout: it's possible for waitUntil() to be called with a timeout in the past. In that
+    // case, waitUntil() will still release the lock and reacquire it. waitUntil() will always return
+    // false in that case. This is subtly different from some pthread_cond_timedwait() implementations,
+    // which may not release the lock for past timeout. But, this behavior is consistent with OpenGroup
+    // documentation for timedwait().
+    template<typename LockType>
+    bool waitUntil(LockType& lock, Clock::time_point timeout)
+    {
+        bool result;
+        if (timeout < Clock::now()) {
+            lock.unlock();
+            result = false;
+        } else {
+            result = ParkingLot::parkConditionally(
+                &m_hasWaiters,
+                [this] () -> bool {
+                    // Let everyone know that we will be waiting. Do this while we hold the queue lock,
+                    // to prevent races with notifyOne().
+                    m_hasWaiters.store(true);
+                    return true;
+                },
+                [&lock] () { lock.unlock(); },
+                timeout);
+        }
+        lock.lock();
+        return result;
+    }
+
+    // Wait until the given predicate is satisfied. Returns true if it is satisfied in the end.
+    // May return early due to timeout.
+    template<typename LockType, typename Functor>
+    bool waitUntil(LockType& lock, Clock::time_point timeout, const Functor& predicate)
+    {
+        while (!predicate()) {
+            if (!waitUntil(lock, timeout))
+                return predicate();
+        }
+        return true;
+    }
+
+    // Wait until the given predicate is satisfied. Returns true if it is satisfied in the end.
+    // May return early due to timeout.
+    template<typename LockType, typename DurationType, typename Functor>
+    bool waitFor(
+        LockType& lock, const DurationType& relativeTimeout, const Functor& predicate)
+    {
+        return waitUntil(lock, absoluteFromRelative(relativeTimeout), predicate);
+    }
+
+    template<typename LockType>
+    void wait(LockType& lock)
+    {
+        waitUntil(lock, Clock::time_point::max());
+    }
+
+    template<typename LockType, typename Functor>
+    void wait(LockType& lock, const Functor& predicate)
+    {
+        while (!predicate())
+            wait(lock);
+    }
+
+    template<typename LockType, typename TimeType>
+    bool waitUntil(LockType& lock, const TimeType& timeout)
+    {
+        if (timeout == TimeType::max()) {
+            wait(lock);
+            return true;
+        }
+        return waitForImpl(lock, timeout - TimeType::clock::now());
+    }
+
+    template<typename LockType>
+    bool waitUntilWallClockSeconds(LockType& lock, double absoluteTimeoutSeconds)
+    {
+        return waitForSecondsImpl(lock, absoluteTimeoutSeconds - currentTime());
+    }
+
+    template<typename LockType>
+    bool waitUntilMonotonicClockSeconds(LockType& lock, double absoluteTimeoutSeconds)
+    {
+        return waitForSecondsImpl(lock, absoluteTimeoutSeconds - monotonicallyIncreasingTime());
+    }
+
+    // Note that this method is extremely fast when nobody is waiting. It is not necessary to try to
+    // avoid calling this method.
+    void notifyOne()
+    {
+        if (!m_hasWaiters.load()) {
+            // At this exact instant, there is nobody waiting on this condition. The way to visualize
+            // this is that if unparkOne() ran to completion without obstructions at this moment, it
+            // wouldn't wake anyone up. Hence, we have nothing to do!
+            return;
+        }
+        
+        ParkingLot::unparkOne(
+            &m_hasWaiters,
+            [this] (bool, bool mayHaveMoreThreads) {
+                if (!mayHaveMoreThreads)
+                    m_hasWaiters.store(false);
+            });
+    }
+    
+    void notifyAll()
+    {
+        if (!m_hasWaiters.load()) {
+            // See above.
+            return;
+        }
+
+        // It's totally safe for us to set this to false without any locking, because this thread is
+        // guaranteed to then unparkAll() anyway. So, if there is a race with some thread calling
+        // wait() just before this store happens, that thread is guaranteed to be awoken by the call to
+        // unparkAll(), below.
+        m_hasWaiters.store(false);
+        
+        ParkingLot::unparkAll(&m_hasWaiters);
+    }
+    
+protected:
+    template<typename LockType>
+    bool waitForSecondsImpl(LockType& lock, double relativeTimeoutSeconds)
+    {
+        double relativeTimeoutNanoseconds = relativeTimeoutSeconds * (1000.0 * 1000.0 * 1000.0);
+        
+        if (!(relativeTimeoutNanoseconds > 0)) {
+            // This handles insta-timeouts as well as NaN.
+            lock.unlock();
+            lock.lock();
+            return false;
+        }
+
+        if (relativeTimeoutNanoseconds > static_cast<double>(std::numeric_limits<int64_t>::max())) {
+            // If the timeout in nanoseconds cannot be expressed using a 64-bit integer, then we
+            // might as well wait forever.
+            wait(lock);
+            return true;
+        }
+        
+        auto relativeTimeout =
+            std::chrono::nanoseconds(static_cast<int64_t>(relativeTimeoutNanoseconds));
+
+        return waitForImpl(lock, relativeTimeout);
+    }
+    
+    template<typename LockType, typename DurationType>
+    bool waitForImpl(LockType& lock, const DurationType& relativeTimeout)
+    {
+        return waitUntil(lock, absoluteFromRelative(relativeTimeout));
+    }
+
+    template<typename DurationType>
+    Clock::time_point absoluteFromRelative(const DurationType& relativeTimeout)
+    {
+        if (relativeTimeout < DurationType::zero())
+            return Clock::time_point::min();
+
+        if (relativeTimeout > Clock::duration::max()) {
+            // This is highly unlikely. But if it happens, we want to not do anything dumb. Sleeping
+            // without a timeout seems sensible when the timeout duration is greater than what can be
+            // expressed using steady_clock.
+            return Clock::time_point::max();
+        }
+        
+        Clock::duration myRelativeTimeout =
+            std::chrono::duration_cast<Clock::duration>(relativeTimeout);
+
+        return Clock::now() + myRelativeTimeout;
+    }
+
+    Atomic<bool> m_hasWaiters;
+};    
+
+class Condition : public ConditionBase {
+    WTF_MAKE_NONCOPYABLE(Condition);
+public:
+    Condition()
+    {
+        m_hasWaiters.store(false);
+    }
+};
+
+typedef ConditionBase StaticCondition;
+
+} // namespace WTF
+
+using WTF::Condition;
+using WTF::StaticCondition;
+
+#endif // WTF_Condition_h
+