[clang-tools-extra] [clangd] [Modules] Support Reusable Modules Builder (PR #106683)

[Chuanqi Xu via cfe-commits]

================
@@ -338,17 +460,129 @@ ModulesBuilder::buildPrerequisiteModulesFor(PathRef File,
   return std::move(RequiredModules);
 }
 
-bool StandalonePrerequisiteModules::canReuse(
+ReusableModulesBuilder::ModuleBuildingSharedOwner
+ReusableModulesBuilder::getOrCreateModuleBuildingOwner(StringRef ModuleName) {
+  std::lock_guard<std::mutex> _(ModulesBuildingMutex);
+
+  auto MutexIter = BuildingModuleMutexes.find(ModuleName);
+  if (MutexIter == BuildingModuleMutexes.end())
+    MutexIter = BuildingModuleMutexes
+                    .try_emplace(ModuleName, std::make_shared<std::mutex>())
+                    .first;
+
+  auto CVIter = BuildingModuleCVs.find(ModuleName);
+  if (CVIter == BuildingModuleCVs.end())
+    CVIter = BuildingModuleCVs
+                 .try_emplace(ModuleName,
+                              std::make_shared<std::condition_variable>())
+                 .first;
+
+  return ModuleBuildingSharedOwner(ModuleName, MutexIter->getValue(),
+                                   CVIter->getValue(), *this);
+}
+
+llvm::Error ReusableModulesBuilder::getOrBuildModuleFile(
+    StringRef ModuleName, const ThreadsafeFS &TFS, ProjectModules &MDB,
+    ReusablePrerequisiteModules &BuiltModuleFiles) {
+  if (BuiltModuleFiles.isModuleUnitBuilt(ModuleName))
+    return llvm::Error::success();
+
+  PathRef ModuleUnitFileName = MDB.getSourceForModuleName(ModuleName);
+  /// It is possible that we're meeting third party modules (modules whose
+  /// source are not in the project. e.g, the std module may be a third-party
+  /// module for most project) or something wrong with the implementation of
+  /// ProjectModules.
+  /// FIXME: How should we treat third party modules here? If we want to ignore
+  /// third party modules, we should return true instead of false here.
+  /// Currently we simply bail out.
+  if (ModuleUnitFileName.empty())
+    return llvm::createStringError(
+        llvm::formatv("Don't get the module unit for module {0}", ModuleName));
+
+  for (auto &RequiredModuleName : MDB.getRequiredModules(ModuleUnitFileName))
+    // Return early if there are errors building the module file.
+    if (!getOrBuildModuleFile(RequiredModuleName, TFS, MDB, BuiltModuleFiles))
+      return llvm::createStringError(
+          llvm::formatv("Failed to build module {0}", RequiredModuleName));
+
+  if (std::shared_ptr<ModuleFile> Cached =
+          getValidModuleFile(ModuleName, MDB, TFS, BuiltModuleFiles)) {
+    log("Reusing module {0} from {1}", ModuleName, Cached->ModuleFilePath);
+    BuiltModuleFiles.addModuleFile(Cached);
+    return llvm::Error::success();
+  }
+
+  ModuleBuildingSharedOwner ModuleBuildingOwner =
+      getOrCreateModuleBuildingOwner(ModuleName);
+
+  std::condition_variable &CV = ModuleBuildingOwner.getCV();
+  std::unique_lock<std::mutex> lk(ModuleBuildingOwner.getMutex());
+  if (!ModuleBuildingOwner.isUniqueBuildingOwner()) {
----------------
ChuanqiXu9 wrote:

I prefer to leave it as is. Otherwise,  two opened file may not be able to share the same BMI that meant to be shared. I feel it is the functionality of the patch. 

https://github.com/llvm/llvm-project/pull/106683