Add SharedPtr, an efficient non-intrusive shared pointer.

Rename `RefCountedPtr` to `IntrusiveSharedPtr` to highlight a relationship to
`SharedPtr`.

Migrate most usages of `IntrusiveSharedPtr` to `SharedPtr`.

Deprecate `RefCountedBase`. It has no more usages in Riegeli. Almost all usages
of `RefCountedPtr` which rely on `RefCountedBase` for intrusive reference
counting can be migrated to `SharedPtr` instead of `IntrusiveSharedPtr`.

Split `intrusive_ref_count.h` to `ref_count.h`, `shared_ptr.h`, and
`intrusive_shared_ptr.h`.

Rename member functions from std style to Google style:
* `reset()` → `Reset()`
* `release()` → `Release()`
* `has_unique_owner()` → `HasUniqueOwner()`

Deprecate `MakeRefCounted()`. Construct the object held by
`{,Intrusive}SharedPtr` using a constructor from `Initializer`. As a bonus,
`Reset()` from `Initializer` can assign to an existing object if possible.

Minor changes to the API:
* Add a direct definition of `IntrusiveSharedPtr::operator=(std::nullptr_t)` to
  complement the implicit conversion.
* Add `IntrusiveSharedPtr::IsUnique()` for consistency with `SharedPtr`.
* Remove `IntrusiveSharedPtr::exchange()`. `std::exchange()` is equally
  efficient.
* Support heterogeneous equality.
* Rename `{,Sized}SharedBuffer::has_unique_owner()` to `IsUnique()`.

In compression dictionaries and `CsvHeader`, simplify code by using
`Initializer<std::string>::AllowingExplicit` instead of pairs of overloads for
`absl::string_view` and `std::string&&` (the latter as a template to avoid
ambiguity).

PiperOrigin-RevId: 629405077

riegeli/base/BUILD

@@ -335,11 +335,30 @@ cc_library(
 )
 
 cc_library(
-    name = "intrusive_ref_count",
-    hdrs = ["intrusive_ref_count.h"],
+    name = "shared_ptr",
+    hdrs = [
+        "intrusive_shared_ptr.h",
+        "ref_count.h",
+        "shared_ptr.h",
+    ],
     deps = [
+        ":arithmetic",
         ":assert",
         ":compare",
+        ":initializer",
+        ":memory_estimator",
+        ":new_aligned",
+        "@com_google_absl//absl/base:core_headers",
+        "@com_google_absl//absl/meta:type_traits",
+    ],
+)
+
+cc_library(
+    name = "intrusive_ref_count",
+    hdrs = ["intrusive_ref_count.h"],
+    deps = [
+        ":initializer",
+        ":shared_ptr",
         "@com_google_absl//absl/base:core_headers",
     ],
 )
@@ -368,7 +387,8 @@ cc_library(
         ":buffer",
         ":buffering",
         ":cord_utils",
-        ":intrusive_ref_count",
+        ":initializer",
+        ":shared_ptr",
         "@com_google_absl//absl/base:core_headers",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/strings:cord",
@@ -402,11 +422,11 @@ cc_library(
         ":compare",
         ":cord_utils",
         ":initializer",
-        ":intrusive_ref_count",
         ":memory_estimator",
         ":new_aligned",
         ":no_destructor",
         ":shared_buffer",
+        ":shared_ptr",
         ":sized_shared_buffer",
         ":string_utils",
         ":zeros",

riegeli/base/chain.cc

@@ -38,7 +38,7 @@
 #include "riegeli/base/buffering.h"
 #include "riegeli/base/compare.h"
 #include "riegeli/base/cord_utils.h"
-#include "riegeli/base/intrusive_ref_count.h"
+#include "riegeli/base/intrusive_shared_ptr.h"
 #include "riegeli/base/maker.h"
 #include "riegeli/base/memory_estimator.h"
 #include "riegeli/base/new_aligned.h"
@@ -302,7 +302,7 @@ class Chain::BlockRef {
   }
 
  private:
-  RefCountedPtr<RawBlock> block_;
+  IntrusiveSharedPtr<RawBlock> block_;
 };
 
 template <Chain::Ownership ownership>
@@ -319,7 +319,7 @@ inline Chain::BlockRef::BlockRef(RawBlock* block,
     block = target;
   }
   if (ownership == Ownership::kShare) block->Ref();
-  block_.reset(block);
+  block_.Reset(block);
 }
 
 void Chain::BlockRef::DumpStructure(absl::string_view data,

riegeli/base/chain.h

@@ -40,9 +40,10 @@
 #include "riegeli/base/buffering.h"
 #include "riegeli/base/compare.h"
 #include "riegeli/base/initializer.h"
-#include "riegeli/base/intrusive_ref_count.h"
+#include "riegeli/base/intrusive_shared_ptr.h"
 #include "riegeli/base/memory_estimator.h"
 #include "riegeli/base/new_aligned.h"
+#include "riegeli/base/ref_count.h"
 #include "riegeli/base/sized_shared_buffer.h"
 
 namespace riegeli {
@@ -828,8 +829,8 @@ class Chain::PinnedBlock {
 
  private:
   friend class BlockIterator;
-  explicit PinnedBlock(RawBlock* block) : block_(block) {}
-  RefCountedPtr<RawBlock> block_;
+  explicit PinnedBlock(RawBlock* block);
+  IntrusiveSharedPtr<RawBlock> block_;
 };
 
 class Chain::Blocks {
@@ -1334,7 +1335,7 @@ void Chain::RawBlock::Unref() {
 }
 
 inline bool Chain::RawBlock::has_unique_owner() const {
-  return ref_count_.has_unique_owner();
+  return ref_count_.HasUniqueOwner();
 }
 
 inline size_t Chain::RawBlock::capacity() const {
@@ -1558,6 +1559,8 @@ inline Chain::PinnedBlock Chain::BlockIterator::Pin() {
   return PinnedBlock(PinImpl());
 }
 
+inline Chain::PinnedBlock::PinnedBlock(RawBlock* block) : block_(block) {}
+
 inline absl::string_view Chain::PinnedBlock::operator*() const {
   RIEGELI_ASSERT(block_ != nullptr)
       << "Failed precondition of Chain::PinnedBlock::operator*: null pointer";
@@ -1579,7 +1582,7 @@ inline void* Chain::PinnedBlock::Share() const& {
 inline void* Chain::PinnedBlock::Share() && {
   RIEGELI_ASSERT(block_ != nullptr)
       << "Failed precondition of Chain::PinnedBlock::Share(): null pointer";
-  return block_.release();
+  return block_.Release();
 }
 
 inline void Chain::PinnedBlock::DeleteShared(void* ptr) {