webkitgtk-2.16.5HEADwebkitgtk-2.16.5master

1 files changed, 196 insertions, 0 deletions

diff --git a/Source/JavaScriptCore/heap/Subspace.cpp b/Source/JavaScriptCore/heap/Subspace.cpp
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+++ b/Source/JavaScriptCore/heap/Subspace.cpp
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+/*
+ * Copyright (C) 2017 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. 
+ */
+
+#include "config.h"
+#include "Subspace.h"
+
+#include "JSCInlines.h"
+#include "MarkedAllocatorInlines.h"
+#include "MarkedBlockInlines.h"
+#include "PreventCollectionScope.h"
+#include "SubspaceInlines.h"
+
+namespace JSC {
+
+namespace {
+
+// Writing it this way ensures that when you pass this as a functor, the callee is specialized for
+// this callback. If you wrote this as a normal function then the callee would be specialized for
+// the function's type and it would have indirect calls to that function. And unlike a lambda, it's
+// possible to mark this ALWAYS_INLINE.
+struct DestroyFunc {
+    ALWAYS_INLINE void operator()(VM& vm, JSCell* cell) const
+    {
+        ASSERT(cell->structureID());
+        ASSERT(cell->inlineTypeFlags() & StructureIsImmortal);
+        Structure* structure = cell->structure(vm);
+        const ClassInfo* classInfo = structure->classInfo();
+        MethodTable::DestroyFunctionPtr destroy = classInfo->methodTable.destroy;
+        destroy(cell);
+    }
+};
+
+} // anonymous namespace
+
+Subspace::Subspace(CString name, Heap& heap, AllocatorAttributes attributes)
+    : m_space(heap.objectSpace())
+    , m_name(name)
+    , m_attributes(attributes)
+{
+    // It's remotely possible that we're GCing right now even if the client is careful to only
+    // create subspaces right after VM creation, since collectContinuously (and probably other
+    // things) could cause a GC to be launched at pretty much any time and it's not 100% obvious
+    // that all clients would be able to ensure that there are zero safepoints between when they
+    // create VM and when they do this. Preventing GC while we're creating the Subspace ensures
+    // that we don't have to worry about whether it's OK for the GC to ever see a brand new
+    // subspace.
+    PreventCollectionScope preventCollectionScope(heap);
+    heap.objectSpace().m_subspaces.append(this);
+    
+    for (size_t i = MarkedSpace::numSizeClasses; i--;)
+        m_allocatorForSizeStep[i] = nullptr;
+}
+
+Subspace::~Subspace()
+{
+}
+
+FreeList Subspace::finishSweep(MarkedBlock::Handle& block, MarkedBlock::Handle::SweepMode sweepMode)
+{
+    return block.finishSweepKnowingSubspace(sweepMode, DestroyFunc());
+}
+
+void Subspace::destroy(VM& vm, JSCell* cell)
+{
+    DestroyFunc()(vm, cell);
+}
+
+// The reason why we distinguish between allocate and tryAllocate is to minimize the number of
+// checks on the allocation path in both cases. Likewise, the reason why we have overloads with and
+// without deferralContext is to minimize the amount of code for calling allocate when you don't
+// need the deferralContext.
+void* Subspace::allocate(size_t size)
+{
+    if (MarkedAllocator* allocator = tryAllocatorFor(size))
+        return allocator->allocate();
+    return allocateSlow(nullptr, size);
+}
+
+void* Subspace::allocate(GCDeferralContext* deferralContext, size_t size)
+{
+    if (MarkedAllocator* allocator = tryAllocatorFor(size))
+        return allocator->allocate(deferralContext);
+    return allocateSlow(deferralContext, size);
+}
+
+void* Subspace::tryAllocate(size_t size)
+{
+    if (MarkedAllocator* allocator = tryAllocatorFor(size))
+        return allocator->tryAllocate();
+    return tryAllocateSlow(nullptr, size);
+}
+
+void* Subspace::tryAllocate(GCDeferralContext* deferralContext, size_t size)
+{
+    if (MarkedAllocator* allocator = tryAllocatorFor(size))
+        return allocator->tryAllocate(deferralContext);
+    return tryAllocateSlow(deferralContext, size);
+}
+
+MarkedAllocator* Subspace::allocatorForSlow(size_t size)
+{
+    size_t index = MarkedSpace::sizeClassToIndex(size);
+    size_t sizeClass = MarkedSpace::s_sizeClassForSizeStep[index];
+    if (!sizeClass)
+        return nullptr;
+    
+    // This is written in such a way that it's OK for the JIT threads to end up here if they want
+    // to generate code that uses some allocator that hadn't been used yet. Note that a possibly-
+    // just-as-good solution would be to return null if we're in the JIT since the JIT treats null
+    // allocator as "please always take the slow path". But, that could lead to performance
+    // surprises and the algorithm here is pretty easy. Only this code has to hold the lock, to
+    // prevent simultaneously MarkedAllocator creations from multiple threads. This code ensures
+    // that any "forEachAllocator" traversals will only see this allocator after it's initialized
+    // enough: it will have 
+    auto locker = holdLock(m_space.allocatorLock());
+    if (MarkedAllocator* allocator = m_allocatorForSizeStep[index])
+        return allocator;
+
+    if (false)
+        dataLog("Creating marked allocator for ", m_name, ", ", m_attributes, ", ", sizeClass, ".\n");
+    MarkedAllocator* allocator = m_space.addMarkedAllocator(locker, this, sizeClass);
+    index = MarkedSpace::sizeClassToIndex(sizeClass);
+    for (;;) {
+        if (MarkedSpace::s_sizeClassForSizeStep[index] != sizeClass)
+            break;
+
+        m_allocatorForSizeStep[index] = allocator;
+        
+        if (!index--)
+            break;
+    }
+    allocator->setNextAllocatorInSubspace(m_firstAllocator);
+    WTF::storeStoreFence();
+    m_firstAllocator = allocator;
+    return allocator;
+}
+
+void* Subspace::allocateSlow(GCDeferralContext* deferralContext, size_t size)
+{
+    void* result = tryAllocateSlow(deferralContext, size);
+    RELEASE_ASSERT(result);
+    return result;
+}
+
+void* Subspace::tryAllocateSlow(GCDeferralContext* deferralContext, size_t size)
+{
+    if (MarkedAllocator* allocator = allocatorFor(size))
+        return allocator->tryAllocate(deferralContext);
+    
+    if (size <= Options::largeAllocationCutoff()
+        && size <= MarkedSpace::largeCutoff) {
+        dataLog("FATAL: attampting to allocate small object using large allocation.\n");
+        dataLog("Requested allocation size: ", size, "\n");
+        RELEASE_ASSERT_NOT_REACHED();
+    }
+    
+    m_space.heap()->collectIfNecessaryOrDefer(deferralContext);
+    
+    size = WTF::roundUpToMultipleOf<MarkedSpace::sizeStep>(size);
+    LargeAllocation* allocation = LargeAllocation::tryCreate(*m_space.m_heap, size, this);
+    if (!allocation)
+        return nullptr;
+    
+    m_space.m_largeAllocations.append(allocation);
+    m_space.m_heap->didAllocate(size);
+    m_space.m_capacity += size;
+    
+    m_largeAllocations.append(allocation);
+        
+    return allocation->cell();
+}
+
+} // namespace JSC
+