Fix reset and deleting behavior.

* Reset the Arena state.
* Call all the dtors before deleting the blocks.

TBR=mtklein@google.com

Change-Id: Iac320fec16e572cc9a6184c1f580089ab720f036
Reviewed-on: https://skia-review.googlesource.com/7221
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>

2 files changed, 38 insertions, 26 deletions

diff --git a/src/core/SkArenaAlloc.cpp b/src/core/SkArenaAlloc.cpp
index d6c249b573..03ab9fad4f 100644
--- a/src/core/SkArenaAlloc.cpp
+++ b/src/core/SkArenaAlloc.cpp
@@ -12,15 +12,21 @@ struct Skipper {
     char* operator()(char* objEnd, ptrdiff_t size) { return objEnd + size; }
 };
 
-struct NextBlock {
-    char* operator()(char* objEnd, ptrdiff_t size) { delete [] objEnd; return objEnd + size; }
+struct SkArenaAlloc::NextBlock {
+    char* operator()(char* objEnd, ptrdiff_t size) {
+        ResetBlock(objEnd + size);
+        delete [] objEnd;
+        return nullptr;
+    }
 };
 
 SkArenaAlloc::SkArenaAlloc(char* block, size_t size, size_t extraSize)
-    : fDtorCursor{block}
-    , fCursor    {block}
-    , fEnd       {block + size}
-    , fExtraSize {extraSize}
+    : fDtorCursor {block}
+    , fCursor     {block}
+    , fEnd        {block + size}
+    , fFirstBlock {block}
+    , fFirstSize  {size}
+    , fExtraSize  {extraSize}
 {
     if (size < sizeof(Footer)) {
         fEnd = fCursor = fDtorCursor = nullptr;
@@ -32,16 +38,12 @@ SkArenaAlloc::SkArenaAlloc(char* block, size_t size, size_t extraSize)
 }
 
 SkArenaAlloc::~SkArenaAlloc() {
-    this->reset();
+    ResetBlock(fDtorCursor);
 }
 
 void SkArenaAlloc::reset() {
-    Footer f;
-    memmove(&f, fDtorCursor - sizeof(Footer), sizeof(Footer));
-    char* releaser = fDtorCursor;
-    while (releaser != nullptr) {
-        releaser = this->callFooterAction(releaser);
-    }
+    this->~SkArenaAlloc();
+    new (this) SkArenaAlloc{fFirstBlock, fFirstSize, fExtraSize};
 }
 
 void SkArenaAlloc::installFooter(FooterAction* releaser, ptrdiff_t padding) {
@@ -54,8 +56,6 @@ void SkArenaAlloc::installFooter(FooterAction* releaser, ptrdiff_t padding) {
 
     Footer footer = (Footer)(footerData);
     memmove(fCursor, &footer, sizeof(Footer));
-    Footer check;
-    memmove(&check, fCursor, sizeof(Footer));
     fCursor += sizeof(Footer);
     fDtorCursor = fCursor;
 }
@@ -104,7 +104,7 @@ char* SkArenaAlloc::allocObject(size_t size, size_t alignment) {
 char* SkArenaAlloc::allocObjectWithFooter(size_t sizeIncludingFooter, size_t alignment) {
     size_t mask = alignment - 1;
 
-    restart:
+restart:
     size_t skipOverhead = 0;
     bool needsSkipFooter = fCursor != fDtorCursor;
     if (needsSkipFooter) {
@@ -132,14 +132,20 @@ char* SkArenaAlloc::allocObjectWithFooter(size_t sizeIncludingFooter, size_t ali
     return objStart;
 }
 
-char* SkArenaAlloc::callFooterAction(char* end) {
+void SkArenaAlloc::ResetBlock(char* footerEnd) {
+    while (footerEnd != nullptr) {
+        footerEnd = CallFooterAction(footerEnd);
+    }
+}
+
+char* SkArenaAlloc::CallFooterAction(char* footerEnd) {
     Footer footer;
-    memcpy(&footer, end - sizeof(Footer), sizeof(Footer));
+    memcpy(&footer, footerEnd - sizeof(Footer), sizeof(Footer));
 
-    FooterAction* releaser = (FooterAction*)((char*)EndChain + (footer >> 5));
+    FooterAction* action = (FooterAction*)((char*)EndChain + (footer >> 5));
     ptrdiff_t padding = footer & 31;
 
-    char* r = releaser(end) - padding;
+    char* r = action(footerEnd) - padding;
 
     return r;
 }
diff --git a/src/core/SkArenaAlloc.h b/src/core/SkArenaAlloc.h
index 8152c94cbd..56006c30b2 100644
--- a/src/core/SkArenaAlloc.h
+++ b/src/core/SkArenaAlloc.h
@@ -56,7 +56,7 @@ public:
     SkArenaAlloc(char* block, size_t size, size_t extraSize = 0);
 
     template <size_t kSize>
-    SkArenaAlloc(char (&block)[kSize], size_t extraSize = 0)
+    SkArenaAlloc(char (&block)[kSize], size_t extraSize = kSize)
         : SkArenaAlloc(block, kSize, extraSize)
     {}
 
@@ -116,6 +116,8 @@ private:
     using Footer = int32_t;
     using FooterAction = char* (char*);
 
+    struct NextBlock;
+
     void installFooter(FooterAction* releaser, ptrdiff_t padding);
 
     // N.B. Action is different than FooterAction. FooterAction expects the end of the Footer,
@@ -179,7 +181,9 @@ private:
         return objStart;
     }
 
-    char* callFooterAction(char* end);
+    static char* CallFooterAction(char* end);
+
+    static void ResetBlock(char* footerEnd);
 
     static char* EndChain(char*);
 
@@ -195,10 +199,12 @@ private:
         }
     };
 
-    char*  fDtorCursor;
-    char*  fCursor;
-    char*  fEnd;
-    size_t fExtraSize;
+    char*        fDtorCursor;
+    char*        fCursor;
+    char*        fEnd;
+    char* const  fFirstBlock;
+    const size_t fFirstSize;
+    const size_t fExtraSize;
 };
 
 #endif//SkFixedAlloc_DEFINED