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+//===- InMemoryModuleCache.h - In-memory cache for modules ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H
+#define LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H
+
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include <memory>
+
+namespace clang {
+
+/// In-memory cache for modules.
+///
+/// This is a cache for modules for use across a compilation, sharing state
+/// between the CompilerInstances in an implicit modules build. It must be
+/// shared by each CompilerInstance, ASTReader, ASTWriter, and ModuleManager
+/// that are coordinating.
+///
+/// Critically, it ensures that a single process has a consistent view of each
+/// PCM. This is used by \a CompilerInstance when building PCMs to ensure that
+/// each \a ModuleManager sees the same files.
+class InMemoryModuleCache : public llvm::RefCountedBase<InMemoryModuleCache> {
+ struct PCM {
+ std::unique_ptr<llvm::MemoryBuffer> Buffer;
+
+ /// Track whether this PCM is known to be good (either built or
+ /// successfully imported by a CompilerInstance/ASTReader using this
+ /// cache).
+ bool IsFinal = false;
+
+ PCM() = default;
+ PCM(std::unique_ptr<llvm::MemoryBuffer> Buffer)
+ : Buffer(std::move(Buffer)) {}
+ };
+
+ /// Cache of buffers.
+ llvm::StringMap<PCM> PCMs;
+
+public:
+ /// There are four states for a PCM. It must monotonically increase.
+ ///
+ /// 1. Unknown: the PCM has neither been read from disk nor built.
+ /// 2. Tentative: the PCM has been read from disk but not yet imported or
+ /// built. It might work.
+ /// 3. ToBuild: the PCM read from disk did not work but a new one has not
+ /// been built yet.
+ /// 4. Final: indicating that the current PCM was either built in this
+ /// process or has been successfully imported.
+ enum State { Unknown, Tentative, ToBuild, Final };
+
+ /// Get the state of the PCM.
+ State getPCMState(llvm::StringRef Filename) const;
+
+ /// Store the PCM under the Filename.
+ ///
+ /// \pre state is Unknown
+ /// \post state is Tentative
+ /// \return a reference to the buffer as a convenience.
+ llvm::MemoryBuffer &addPCM(llvm::StringRef Filename,
+ std::unique_ptr<llvm::MemoryBuffer> Buffer);
+
+ /// Store a just-built PCM under the Filename.
+ ///
+ /// \pre state is Unknown or ToBuild.
+ /// \pre state is not Tentative.
+ /// \return a reference to the buffer as a convenience.
+ llvm::MemoryBuffer &addBuiltPCM(llvm::StringRef Filename,
+ std::unique_ptr<llvm::MemoryBuffer> Buffer);
+
+ /// Try to remove a buffer from the cache. No effect if state is Final.
+ ///
+ /// \pre state is Tentative/Final.
+ /// \post Tentative => ToBuild or Final => Final.
+ /// \return false on success, i.e. if Tentative => ToBuild.
+ bool tryToDropPCM(llvm::StringRef Filename);
+
+ /// Mark a PCM as final.
+ ///
+ /// \pre state is Tentative or Final.
+ /// \post state is Final.
+ void finalizePCM(llvm::StringRef Filename);
+
+ /// Get a pointer to the pCM if it exists; else nullptr.
+ llvm::MemoryBuffer *lookupPCM(llvm::StringRef Filename) const;
+
+ /// Check whether the PCM is final and has been shown to work.
+ ///
+ /// \return true iff state is Final.
+ bool isPCMFinal(llvm::StringRef Filename) const;
+
+ /// Check whether the PCM is waiting to be built.
+ ///
+ /// \return true iff state is ToBuild.
+ bool shouldBuildPCM(llvm::StringRef Filename) const;
+};
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H