1 files changed, 173 insertions, 0 deletions
diff --git a/intl/lwbrk/nsComplexBreaker.cpp b/intl/lwbrk/nsComplexBreaker.cpp
new file mode 100644
index 0000000000..0c0a5e45b6
--- /dev/null
+++ b/intl/lwbrk/nsComplexBreaker.cpp
@@ -0,0 +1,173 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsComplexBreaker.h"
+
+#include <algorithm>
+
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Services.h"
+#include "mozilla/UniquePtr.h"
+#include "nsTHashMap.h"
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla;
+
+using CacheMap = nsTHashMap<nsString, nsTArray<uint8_t>>;
+
+static UniquePtr<CacheMap> sBreakCache;
+
+// The underlying hash table extends capacity, when it hits .75 full and uses
+// powers of 2 for sizing. This cache limit will hopefully mean most pages fit
+// within the cache, while keeping it to a reasonable size. Also by holding the
+// previous cache even if pages are bigger than the cache the most commonly used
+// should still remain fast.
+static const int kCacheLimit = 3072;
+
+static UniquePtr<CacheMap> sOldBreakCache;
+
+// Simple runnable to delete caches off the main thread.
+class CacheDeleter final : public Runnable {
+ public:
+  explicit CacheDeleter(UniquePtr<CacheMap> aCacheToDelete)
+      : Runnable("ComplexBreaker CacheDeleter"),
+        mCacheToDelete(std::move(aCacheToDelete)) {}
+
+  NS_IMETHOD Run() override {
+    MOZ_ASSERT(!NS_IsMainThread());
+    mCacheToDelete = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  UniquePtr<CacheMap> mCacheToDelete;
+};
+
+class ComplexBreakObserver final : public nsIObserver {
+  ~ComplexBreakObserver() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+};
+
+NS_IMPL_ISUPPORTS(ComplexBreakObserver, nsIObserver)
+
+NS_IMETHODIMP ComplexBreakObserver::Observe(nsISupports* aSubject,
+                                            const char* aTopic,
+                                            const char16_t* aData) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (strcmp(aTopic, "memory-pressure") == 0) {
+    if (sOldBreakCache) {
+      // We have an old cache, so delete that one first.
+      NS_DispatchBackgroundTask(
+          MakeAndAddRef<CacheDeleter>(std::move(sOldBreakCache)));
+    } else if (sBreakCache) {
+      NS_DispatchBackgroundTask(
+          MakeAndAddRef<CacheDeleter>(std::move(sBreakCache)));
+    }
+  }
+
+  return NS_OK;
+}
+
+void ComplexBreaker::Initialize() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (obs) {
+    obs->AddObserver(new ComplexBreakObserver(), "memory-pressure", false);
+  }
+}
+
+void ComplexBreaker::Shutdown() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  sBreakCache = nullptr;
+  sOldBreakCache = nullptr;
+}
+
+static void AddToCache(const char16_t* aText, uint32_t aLength,
+                       nsTArray<uint8_t> aBreakBefore) {
+  if (NS_WARN_IF(!sBreakCache->InsertOrUpdate(
+          nsString(aText, aLength), std::move(aBreakBefore), fallible))) {
+    return;
+  }
+
+  if (sBreakCache->Count() <= kCacheLimit) {
+    return;
+  }
+
+  if (sOldBreakCache) {
+    NS_DispatchBackgroundTask(
+        MakeAndAddRef<CacheDeleter>(std::move(sOldBreakCache)));
+  }
+
+  sOldBreakCache = std::move(sBreakCache);
+}
+
+static void CopyAndFill(const nsTArray<uint8_t>& aCachedBreakBefore,
+                        uint8_t* aBreakBefore, uint8_t* aEndBreakBefore) {
+  auto* startFill = std::copy(aCachedBreakBefore.begin(),
+                              aCachedBreakBefore.end(), aBreakBefore);
+  std::fill(startFill, aEndBreakBefore, false);
+}
+
+void ComplexBreaker::GetBreaks(const char16_t* aText, uint32_t aLength,
+                               uint8_t* aBreakBefore) {
+  // It is believed that this is only called on the main thread, so we don't
+  // need to lock the caching structures. A diagnostic assert is used in case
+  // our tests don't exercise all code paths.
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
+
+  MOZ_ASSERT(aText, "aText shouldn't be null");
+  MOZ_ASSERT(aLength, "aLength shouldn't be zero");
+  MOZ_ASSERT(aBreakBefore, "aBreakBefore shouldn't be null");
+
+  // If we have a cache then check it, if not then create it.
+  if (sBreakCache) {
+    if (auto entry =
+            sBreakCache->Lookup(nsDependentSubstring(aText, aLength))) {
+      auto& breakBefore = entry.Data();
+      CopyAndFill(breakBefore, aBreakBefore, aBreakBefore + aLength);
+      return;
+    }
+  } else {
+    sBreakCache = MakeUnique<CacheMap>();
+  }
+
+  // We keep the previous cache when we hit our limit, so that the most recently
+  // used fragments remain fast.
+  if (sOldBreakCache) {
+    auto breakBefore =
+        sOldBreakCache->Extract(nsDependentSubstring(aText, aLength));
+    if (breakBefore) {
+      CopyAndFill(*breakBefore, aBreakBefore, aBreakBefore + aLength);
+      // Move the entry to the latest cache.
+      AddToCache(aText, aLength, std::move(*breakBefore));
+      return;
+    }
+  }
+
+  NS_GetComplexLineBreaks(aText, aLength, aBreakBefore);
+
+  // As a very simple memory saving measure we trim off trailing elements that
+  // are false before caching.
+  auto* afterLastTrue = aBreakBefore + aLength;
+  while (!*(afterLastTrue - 1)) {
+    if (--afterLastTrue == aBreakBefore) {
+      break;
+    }
+  }
+
+  AddToCache(aText, aLength,
+             nsTArray<uint8_t>(aBreakBefore, afterLastTrue - aBreakBefore));
+}