[gin] Introduce gin::MaybeShutdownCppgc()

crrev.com/875699 introduced gin::InitializeCppgcFromV8Platform(), which
centralized initialization of cppgc in Gin for the case of multiple
cppgc users in the same process.

Introduce gin::MaybeShutdownCppgc(), which centralizes the shutdown of
cppgc in Gin. This will help in guaranteeing that cppgc is shutdown only
after all users in the same process are done using it.

Bug: 1056170, 1111024
Change-Id: I15aebd3bea78a7033cf00743dbd4e286b1a30711
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3011899
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#899637}

gin/cppgc.cc

@@ -3,19 +3,33 @@
 // found in the LICENSE file.
 
 #include "gin/public/cppgc.h"
+
+#include "base/check_op.h"
 #include "gin/public/v8_platform.h"
 #include "v8/include/cppgc/platform.h"
 
 namespace gin {
 
+namespace {
+
+int g_init_count = 0;
+
+}  // namespace
+
 void InitializeCppgcFromV8Platform() {
-  static bool cppgc_is_initialized = false;
-  if (cppgc_is_initialized)
+  DCHECK_GE(g_init_count, 0);
+  if (g_init_count++ > 0)
     return;
 
   cppgc::InitializeProcess(gin::V8Platform::Get()->GetPageAllocator());
+}
 
-  cppgc_is_initialized = true;
+void MaybeShutdownCppgc() {
+  DCHECK_GT(g_init_count, 0);
+  if (--g_init_count > 0)
+    return;
+
+  cppgc::ShutdownProcess();
 }
 
 }  // namespace gin

gin/public/cppgc.h

@@ -9,8 +9,17 @@
 
 namespace gin {
 
+// A wrapper around `cppgc::InitializeProcess()` which helps to guarantee that
+// cppgc is initialized only once when there are multiple users of cppgc in same
+// process.
 GIN_EXPORT void InitializeCppgcFromV8Platform();
 
+// Calls `cppgc::ShutdownProcess()` only after being called as many times as
+// `InitializeCppgcFromV8Platform()`. Helps to guarantee that cppgc is shutdown
+// only after all users in the same process are done using it. Number of calls
+// cannot exceed that of `InitializeCppgcFromV8Platform()`.
+GIN_EXPORT void MaybeShutdownCppgc();
+
 }  // namespace gin
 
-#endif  // GIN_PUBLIC_CPPGC_H_
+#endif  // GIN_PUBLIC_CPPGC_H_

pdf/pdfium/pdfium_engine.cc

@@ -31,7 +31,6 @@
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "gin/array_buffer.h"
-#include "gin/public/cppgc.h"
 #include "gin/public/gin_embedders.h"
 #include "gin/public/isolate_holder.h"
 #include "gin/public/v8_platform.h"
@@ -81,7 +80,7 @@
 #include "v8/include/v8.h"
 
 #if defined(PDF_ENABLE_XFA)
-#include "v8/include/cppgc/platform.h"
+#include "gin/public/cppgc.h"
 #endif
 
 #if defined(OS_LINUX) || defined(OS_CHROMEOS)
@@ -266,7 +265,7 @@ void SetUpV8() {
 
 void TearDownV8() {
 #if defined(PDF_ENABLE_XFA)
-  cppgc::ShutdownProcess();
+  gin::MaybeShutdownCppgc();
 #endif
 
   delete g_isolate_holder;