Handle tags now work with heap allocated handles (#8370)

- uninlined getHandleTag so that the code is not duplicated when
  multiple backends are supported (e.g. GLES and Vulkan)
- added a lock for mDebugTags because, even if rare, it technically
  can be accessed from multiple threads. This would happen only
  on a failure. There should never be any contention on this lock.

filament/backend/include/private/backend/HandleAllocator.h

@@ -31,6 +31,7 @@
 
 #include <cstddef>
 #include <exception>
+#include <mutex>
 #include <type_traits>
 #include <unordered_map>
 #include <utility>
@@ -44,11 +45,26 @@
 
 namespace filament::backend {
 
+// This is used to not duplicate the code for the Tags management
+class DebugTag {
+public:
+    DebugTag();
+    void writeHandleTag(HandleBase::HandleId key, utils::CString&& tag) noexcept;
+    utils::CString findHandleTag(HandleBase::HandleId key) const noexcept;
+
+private:
+    // This is used to associate a tag to a handle. mDebugTags is only written the in the main
+    // driver thread, but it can be accessed from any thread, because it's called from handle_cast<>
+    // which is used by synchronous calls.
+    mutable utils::Mutex mDebugTagLock;
+    tsl::robin_map<HandleBase::HandleId, utils::CString> mDebugTags;
+};
+
 /*
  * A utility class to efficiently allocate and manage Handle<>
  */
 template<size_t P0, size_t P1, size_t P2>
-class HandleAllocator {
+class HandleAllocator : public DebugTag {
 public:
     HandleAllocator(const char* name, size_t size, bool disableUseAfterFreeCheck) noexcept;
     HandleAllocator(HandleAllocator const& rhs) = delete;
@@ -200,6 +216,8 @@ class HandleAllocator {
         return static_cast<Dp>(p);
     }
 
+    utils::CString getHandleTag(HandleBase::HandleId key) const noexcept;
+
     template<typename B>
     bool is_valid(Handle<B>& handle) {
         if (!handle) {
@@ -227,24 +245,12 @@ class HandleAllocator {
     void associateTagToHandle(HandleBase::HandleId id, utils::CString&& tag) noexcept {
         // TODO: for now, only pool handles check for use-after-free, so we only keep tags for
         // those
-        if (isPoolHandle(id)) {
+        uint32_t key = id;
+        if (UTILS_LIKELY(isPoolHandle(id))) {
             // Truncate the age to get the debug tag
-            uint32_t const key = id & ~(HANDLE_DEBUG_TAG_MASK ^ HANDLE_AGE_MASK);
-            // This line is the costly part. In the future, we could potentially use a custom
-            // allocator.
-            mDebugTags[key] = std::move(tag);
+            key &= ~(HANDLE_DEBUG_TAG_MASK ^ HANDLE_AGE_MASK);
         }
-    }
-
-    utils::CString getHandleTag(HandleBase::HandleId id) const noexcept {
-        if (!isPoolHandle(id)) {
-            return "(no tag)";
-        }
-        uint32_t const key = id & ~(HANDLE_DEBUG_TAG_MASK ^ HANDLE_AGE_MASK);
-        if (auto pos = mDebugTags.find(key); pos != mDebugTags.end()) {
-            return pos->second;
-        }
-        return "(no tag)";
+        writeHandleTag(key, std::move(tag));
     }
 
 private:
@@ -347,9 +353,8 @@ class HandleAllocator {
         if (UTILS_LIKELY(p)) {
             uint32_t const tag = (uint32_t(age) << HANDLE_AGE_SHIFT) & HANDLE_AGE_MASK;
             return arenaPointerToHandle(p, tag);
-        } else {
-            return allocateHandleSlow(SIZE);
         }
+        return allocateHandleSlow(SIZE);
     }
 
     template<size_t SIZE>
@@ -421,7 +426,6 @@ class HandleAllocator {
     // Below is only used when running out of space in the HandleArena
     mutable utils::Mutex mLock;
     tsl::robin_map<HandleBase::HandleId, void*> mOverflowMap;
-    tsl::robin_map<HandleBase::HandleId, utils::CString> mDebugTags;
     HandleBase::HandleId mId = 0;
     bool mUseAfterFreeCheckDisabled = false;
 };

filament/backend/src/HandleAllocator.cpp

@@ -19,6 +19,7 @@
 #include <backend/Handle.h>
 
 #include <utils/Allocator.h>
+#include <utils/CString.h>
 #include <utils/Log.h>
 #include <utils/Panic.h>
 #include <utils/compiler.h>
@@ -29,7 +30,9 @@
 #include <exception>
 #include <limits>
 #include <mutex>
+#include <utility>
 
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -80,9 +83,6 @@ HandleAllocator<P0, P1, P2>::HandleAllocator(const char* name, size_t size,
         bool disableUseAfterFreeCheck) noexcept
     : mHandleArena(name, size, disableUseAfterFreeCheck),
       mUseAfterFreeCheckDisabled(disableUseAfterFreeCheck) {
-    // Reserve initial space for debug tags. This prevents excessive calls to malloc when the first
-    // few tags are set.
-    mDebugTags.reserve(512);
 }
 
 template <size_t P0, size_t P1, size_t P2>
@@ -147,6 +147,42 @@ void HandleAllocator<P0, P1, P2>::deallocateHandleSlow(HandleBase::HandleId id,
     ::free(p);
 }
 
+template<size_t P0, size_t P1, size_t P2>
+UTILS_NOINLINE
+CString HandleAllocator<P0, P1, P2>::getHandleTag(HandleBase::HandleId id) const noexcept {
+    uint32_t key = id;
+    if (UTILS_LIKELY(isPoolHandle(id))) {
+        // Truncate the age to get the debug tag
+        key &= ~(HANDLE_DEBUG_TAG_MASK ^ HANDLE_AGE_MASK);
+    }
+    return findHandleTag(key);
+}
+
+DebugTag::DebugTag() {
+    // Reserve initial space for debug tags. This prevents excessive calls to malloc when the first
+    // few tags are set.
+    mDebugTags.reserve(512);
+}
+
+UTILS_NOINLINE
+CString DebugTag::findHandleTag(HandleBase::HandleId key) const noexcept {
+    std::unique_lock const lock(mDebugTagLock);
+    if (auto pos = mDebugTags.find(key); pos != mDebugTags.end()) {
+        return pos->second;
+    }
+    return "(no tag)";
+}
+
+UTILS_NOINLINE
+void DebugTag::writeHandleTag(HandleBase::HandleId key, CString&& tag) noexcept {
+    // This line is the costly part. In the future, we could potentially use a custom
+    // allocator.
+    std::unique_lock const lock(mDebugTagLock);
+    // Pool based tags will be recycled after a certain age. Heap-based tag will never be recycled, therefore,
+    // this can grow indefinitely, once we're in the slow mode.
+    mDebugTags[key] = std::move(tag);
+}
+
 // Explicit template instantiations.
 #if defined (FILAMENT_SUPPORTS_OPENGL)
 template class HandleAllocatorGL;