Revert "Reland: implement a function to convert a storage to copy-on-…

…write (pytorch#110022)"

This reverts commit dddf07e.

Reverted pytorch#110022 on behalf of https://github.com/atalman due to New tests are failing in internal CI ([comment](pytorch#110022 (comment)))

c10/core/build.bzl

@@ -58,29 +58,30 @@ def define_targets(rules):
             [
                 "*.cpp",
                 "impl/*.cpp",
-                "impl/cow/*.cpp",
             ],
             exclude = [
                 "CPUAllocator.cpp",
                 "impl/alloc_cpu.cpp",
+                "impl/cow/*.cpp",
             ],
         ),
         hdrs = rules.glob(
             [
                 "*.h",
                 "impl/*.h",
-                "impl/cow/*.h",
             ],
             exclude = [
                 "CPUAllocator.h",
                 "impl/alloc_cpu.h",
+                "impl/cow/*.h",
             ],
         ),
         linkstatic = True,
         local_defines = ["C10_BUILD_MAIN_LIB"],
         visibility = ["//visibility:public"],
         deps = [
             ":ScalarType",
+            ":impl_cow_context",
             "//third_party/cpuinfo",
             "//c10/macros",
             "//c10/util:TypeCast",
@@ -92,6 +93,23 @@ def define_targets(rules):
         alwayslink = True,
     )
 
+    rules.cc_library(
+        name = "impl_cow_context",
+        srcs = [
+            "impl/cow/context.cpp",
+            "impl/cow/deleter.cpp",
+        ],
+        hdrs = [
+            "impl/cow/context.h",
+            "impl/cow/deleter.h",
+        ],
+        deps = [
+            "//c10/macros",
+            "//c10/util:base",
+        ],
+        visibility = ["//c10/test:__pkg__"],
+    )
+
     rules.filegroup(
         name = "headers",
         srcs = rules.glob(

c10/test/build.bzl

@@ -9,6 +9,15 @@ def define_targets(rules):
         visibility = ["//:__pkg__"],
     )
 
+    rules.cc_test(
+        name = "core_impl_cow_context_test",
+        srcs = ["core/impl/cow/context_test.cpp"],
+        deps = [
+            "//c10/core:impl_cow_context",
+            "@com_google_googletest//:gtest_main",
+        ],
+    )
+
     rules.cc_test(
         name = "core_tests",
         size = "small",
@@ -20,7 +29,6 @@ def define_targets(rules):
         deps = [
             "//c10/core:base",
             "//c10/util:base",
-            "//c10/core:CPUAllocator",
             "@com_google_googletest//:gtest_main",
         ],
     )

c10/test/core/impl/cow/context_test.cpp

@@ -0,0 +1,76 @@
+#include <c10/core/impl/cow/context.h>
+
+#include <c10/core/impl/cow/deleter.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+namespace c10::impl {
+namespace {
+
+class DeleteTracker {
+ public:
+  explicit DeleteTracker(int& delete_count) : delete_count_(delete_count) {}
+  ~DeleteTracker() {
+    ++delete_count_;
+  }
+
+ private:
+  int& delete_count_;
+};
+
+class ContextTest : public testing::Test {
+ protected:
+  auto delete_count() const -> int {
+    return delete_count_;
+  }
+  auto new_delete_tracker() -> std::unique_ptr<void, DeleterFnPtr> {
+    return {new DeleteTracker(delete_count_), +[](void* ptr) {
+              delete static_cast<DeleteTracker*>(ptr);
+            }};
+  }
+
+ private:
+  int delete_count_ = 0;
+};
+
+TEST_F(ContextTest, Basic) {
+  auto& context = *new cow::Context(new_delete_tracker());
+  ASSERT_THAT(delete_count(), testing::Eq(0));
+
+  context.increment_refcount();
+
+  {
+    // This is in a sub-scope because this call to decrement_refcount
+    // is expected to give us a shared lock.
+    auto result = context.decrement_refcount();
+    ASSERT_THAT(
+        std::holds_alternative<cow::Context::NotLastReference>(result),
+        testing::IsTrue());
+    ASSERT_THAT(delete_count(), testing::Eq(0));
+  }
+
+  {
+    auto result = context.decrement_refcount();
+    ASSERT_THAT(
+        std::holds_alternative<cow::Context::LastReference>(result),
+        testing::IsTrue());
+    // Result holds the DeleteTracker.
+    ASSERT_THAT(delete_count(), testing::Eq(0));
+  }
+
+  // When result is deleted, the DeleteTracker is also deleted.
+  ASSERT_THAT(delete_count(), testing::Eq(1));
+}
+
+TEST_F(ContextTest, delete_context) {
+  // This is effectively the same thing as decrement_refcount() above.
+  auto& context = *new cow::Context(new_delete_tracker());
+  ASSERT_THAT(delete_count(), testing::Eq(0));
+
+  cow::delete_context(&context);
+  ASSERT_THAT(delete_count(), testing::Eq(1));
+}
+
+} // namespace
+} // namespace c10::impl