b=569770 part 3: provide public access to gfxFontEntry font table cache r=jfkthame

--HG--
extra : rebase_source : ea989eec6d22c0201a58cbe0bb045470e14907f0

gfx/thebes/gfxDWriteFonts.cpp

@@ -419,7 +419,10 @@ gfxDWriteFont::GetFontTable(PRUint32 aTag)
     if (mFontEntry->IsUserFont() && !mFontEntry->IsLocalUserFont()) {
         // for downloaded fonts, there may be layout tables cached in the entry
         // even though they're absent from the sanitized platform font
-        return mFontEntry->GetFontTable(aTag);
+        hb_blob_t *blob;
+        if (mFontEntry->GetExistingFontTable(aTag, &blob)) {
+            return blob;
+        }
     }
 
     return nsnull;

gfx/thebes/gfxFont.cpp

@@ -317,8 +317,8 @@ gfxFontEntry::FontTableHashEntry::GetBlob() const
     return hb_blob_reference(mBlob);
 }
 
-hb_blob_t *
-gfxFontEntry::GetFontTable(PRUint32 aTag)
+PRBool
+gfxFontEntry::GetExistingFontTable(PRUint32 aTag, hb_blob_t **aBlob)
 {
     if (!mFontTableCache.IsInitialized()) {
         // we do this here rather than on fontEntry construction
@@ -327,21 +327,36 @@ gfxFontEntry::GetFontTable(PRUint32 aTag)
     }
 
     FontTableHashEntry *entry = mFontTableCache.GetEntry(aTag);
-    if (entry) {
-        return entry->GetBlob();
+    if (!entry) {
+        return PR_FALSE;
     }
 
-    entry = mFontTableCache.PutEntry(aTag);
+    *aBlob = entry->GetBlob();
+    return PR_TRUE;
+}
+
+hb_blob_t *
+gfxFontEntry::ShareFontTableAndGetBlob(PRUint32 aTag,
+                                       nsTArray<PRUint8>* aBuffer)
+{
+    if (NS_UNLIKELY(!mFontTableCache.IsInitialized())) {
+        // we do this here rather than on fontEntry construction
+        // because not all shapers will access the table cache at all
+        mFontTableCache.Init(10);
+    }
+
+    FontTableHashEntry *entry = mFontTableCache.PutEntry(aTag);
     if (NS_UNLIKELY(!entry)) { // OOM
         return nsnull;
     }
 
-    nsTArray<PRUint8> buffer;
-    if (NS_FAILED(GetFontTable(aTag, buffer))) {
-        return nsnull; // leaves the null entry cached in the hashtable
+    if (!aBuffer) {
+        // ensure the entry is null
+        entry->Clear();
+        return nsnull;
     }
 
-    return entry->ShareTableAndGetBlob(buffer, &mFontTableCache);
+    return entry->ShareTableAndGetBlob(*aBuffer, &mFontTableCache);
 }
 
 void
@@ -1037,6 +1052,19 @@ gfxFont::~gfxFont()
     }
 }
 
+hb_blob_t *
+gfxFont::GetFontTable(PRUint32 aTag) {
+    hb_blob_t *blob;
+    if (mFontEntry->GetExistingFontTable(aTag, &blob))
+        return blob;
+
+    nsTArray<PRUint8> buffer;
+    PRBool haveTable = NS_SUCCEEDED(mFontEntry->GetFontTable(aTag, buffer));
+
+    return mFontEntry->ShareFontTableAndGetBlob(aTag,
+                                                haveTable ? &buffer : nsnull);
+}
+
 /**
  * A helper function in case we need to do any rounding or other
  * processing here.

gfx/thebes/gfxFont.h

@@ -286,12 +286,23 @@ public:
     already_AddRefed<gfxFont> FindOrMakeFont(const gfxFontStyle *aStyle,
                                              PRBool aNeedsBold);
 
-    // Subclasses should override this if they can do something more efficient
-    // than getting tables with GetFontTable() and caching them in the entry.
+    // Get an existing font table cache entry in aBlob if it has been
+    // registered, or return PR_FALSE if not.  Callers must call
+    // hb_blob_destroy on aBlob if PR_TRUE is returned.
     //
     // Note that some gfxFont implementations may not call this at all,
     // if it is more efficient to get the table from the OS at that level.
-    virtual hb_blob_t *GetFontTable(PRUint32 aTag);
+    PRBool GetExistingFontTable(PRUint32 aTag, hb_blob_t** aBlob);
+
+    // Elements of aTable are transferred (not copied) to and returned in a
+    // new hb_blob_t which is registered on the gfxFontEntry, but the initial
+    // reference is owned by the caller.  Removing the last reference
+    // unregisters the table from the font entry.
+    //
+    // Pass NULL for aBuffer to indicate that the table is not present and
+    // NULL will be returned.  Also returns NULL on OOM.
+    hb_blob_t *ShareFontTableAndGetBlob(PRUint32 aTag,
+                                        nsTArray<PRUint8>* aTable);
 
     // Preload a font table into the cache (used to store layout tables for
     // harfbuzz, when they will be stripped from the actual sfnt being
@@ -978,15 +989,16 @@ public:
     // returns a pointer to data owned by the fontEntry or the OS,
     // which will remain valid until released.
     //
-    // Default implementations forward to the font entry, which
-    // maintains a shared table cache; however, subclasses may
-    // override if they can provide more efficient table access.
-
-    // Get pointer to a specific font table, or an empty blob if
+    // Default implementations forward to the font entry,
+    // and maintain a shared table.
+    //
+    // Subclasses should override this if they can provide more efficient
+    // access than getting tables with mFontEntry->GetFontTable() and sharing
+    // them via the entry.
+    //
+    // Get pointer to a specific font table, or NULL if
     // the table doesn't exist in the font
-    virtual hb_blob_t *GetFontTable(PRUint32 aTag) {
-        return mFontEntry->GetFontTable(aTag);
-    }
+    virtual hb_blob_t *GetFontTable(PRUint32 aTag);
 
     // subclasses may provide hinted glyph widths (in font units);
     // if they do not override this, harfbuzz will use unhinted widths

gfx/thebes/gfxMacFont.cpp

@@ -384,7 +384,10 @@ gfxMacFont::GetFontTable(PRUint32 aTag)
     if (mFontEntry->IsUserFont() && !mFontEntry->IsLocalUserFont()) {
         // for downloaded fonts, there may be layout tables cached in the entry
         // even though they're absent from the sanitized platform font
-        return mFontEntry->GetFontTable(aTag);
+        hb_blob_t *blob;
+        if (mFontEntry->GetExistingFontTable(aTag, &blob)) {
+            return blob;
+        }
     }
 
     return nsnull;