Modify the localCache API to require an explicit commit on CachedFile… (#115331)

…Stream.

CachedFileStream has previously performed the commit step in its
destructor, but this means its only recourse for error handling is
report_fatal_error. Modify this to add an explicit commit() method, and
call this in the appropriate places with appropriate error handling for
the location.

Currently the destructor of CacheStream gives an assert failure in Debug
builds if commit() was not called. This will help track down any
remaining uses of the API that assume the old destructior behaviour. In
Release builds we fall back to the previous behaviour and call
report_fatal_error if the commit fails.

lldb/source/Core/DataFileCache.cpp

@@ -132,6 +132,11 @@ bool DataFileCache::SetCachedData(llvm::StringRef key,
       if (file_or_err) {
         llvm::CachedFileStream *cfs = file_or_err->get();
         cfs->OS->write((const char *)data.data(), data.size());
+        if (llvm::Error err = cfs->commit()) {
+          Log *log = GetLog(LLDBLog::Modules);
+          LLDB_LOG_ERROR(log, std::move(err),
+                         "failed to commit to the cache for key: {0}");
+        }
         return true;
       } else {
         Log *log = GetLog(LLDBLog::Modules);

llvm/include/llvm/Support/Caching.h

@@ -24,15 +24,32 @@ class MemoryBuffer;
 /// This class wraps an output stream for a file. Most clients should just be
 /// able to return an instance of this base class from the stream callback, but
 /// if a client needs to perform some action after the stream is written to,
-/// that can be done by deriving from this class and overriding the destructor.
+/// that can be done by deriving from this class and overriding the destructor
+/// or the commit() method.
 class CachedFileStream {
 public:
   CachedFileStream(std::unique_ptr<raw_pwrite_stream> OS,
                    std::string OSPath = "")
       : OS(std::move(OS)), ObjectPathName(OSPath) {}
+
+  /// Must be called exactly once after the writes to OS have been completed
+  /// but before the CachedFileStream object is destroyed.
+  virtual Error commit() {
+    if (Committed)
+      return createStringError(make_error_code(std::errc::invalid_argument),
+                               Twine("CacheStream already committed."));
+    Committed = true;
+
+    return Error::success();
+  }
+
+  bool Committed = false;
   std::unique_ptr<raw_pwrite_stream> OS;
   std::string ObjectPathName;
-  virtual ~CachedFileStream() = default;
+  virtual ~CachedFileStream() {
+    if (!Committed)
+      report_fatal_error("CachedFileStream was not committed.\n");
+  }
 };
 
 /// This type defines the callback to add a file that is generated on the fly.

llvm/lib/CGData/CodeGenData.cpp

@@ -233,6 +233,9 @@ void saveModuleForTwoRounds(const Module &TheModule, unsigned Task,
 
   WriteBitcodeToFile(TheModule, *Stream->OS,
                      /*ShouldPreserveUseListOrder=*/true);
+
+  if (Error Err = Stream->commit())
+    report_fatal_error(std::move(Err));
 }
 
 std::unique_ptr<Module> loadModuleForTwoRounds(BitcodeModule &OrigModule,

llvm/lib/Debuginfod/Debuginfod.cpp

@@ -188,6 +188,11 @@ class StreamedHTTPResponseHandler : public HTTPResponseHandler {
 public:
   StreamedHTTPResponseHandler(CreateStreamFn CreateStream, HTTPClient &Client)
       : CreateStream(CreateStream), Client(Client) {}
+
+  /// Must be called exactly once after the writes have been completed
+  /// but before the StreamedHTTPResponseHandler object is destroyed.
+  Error commit();
+
   virtual ~StreamedHTTPResponseHandler() = default;
 
   Error handleBodyChunk(StringRef BodyChunk) override;
@@ -210,6 +215,12 @@ Error StreamedHTTPResponseHandler::handleBodyChunk(StringRef BodyChunk) {
   return Error::success();
 }
 
+Error StreamedHTTPResponseHandler::commit() {
+  if (FileStream)
+    return FileStream->commit();
+  return Error::success();
+}
+
 // An over-accepting simplification of the HTTP RFC 7230 spec.
 static bool isHeader(StringRef S) {
   StringRef Name;
@@ -298,6 +309,8 @@ Expected<std::string> getCachedOrDownloadArtifact(
       Error Err = Client.perform(Request, Handler);
       if (Err)
         return std::move(Err);
+      if (Err = Handler.commit())
+        return std::move(Err);
 
       unsigned Code = Client.responseCode();
       if (Code && Code != 200)

llvm/lib/LTO/LTOBackend.cpp

@@ -460,6 +460,9 @@ static void codegen(const Config &Conf, TargetMachine *TM,
 
   if (DwoOut)
     DwoOut->keep();
+
+  if (Error Err = Stream->commit())
+    report_fatal_error(std::move(Err));
 }
 
 static void splitCodeGen(const Config &C, TargetMachine *TM,

llvm/lib/Support/Caching.cpp

@@ -88,9 +88,10 @@ Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
             AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),
             ModuleName(ModuleName), Task(Task) {}
 
-      ~CacheStream() {
-        // TODO: Manually commit rather than using non-trivial destructor,
-        // allowing to replace report_fatal_errors with a return Error.
+      Error commit() override {
+        Error E = CachedFileStream::commit();
+        if (E)
+          return E;
 
         // Make sure the stream is closed before committing it.
         OS.reset();
@@ -100,10 +101,12 @@ Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
             MemoryBuffer::getOpenFile(
                 sys::fs::convertFDToNativeFile(TempFile.FD), ObjectPathName,
                 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
-        if (!MBOrErr)
-          report_fatal_error(Twine("Failed to open new cache file ") +
-                             TempFile.TmpName + ": " +
-                             MBOrErr.getError().message() + "\n");
+        if (!MBOrErr) {
+          std::error_code EC = MBOrErr.getError();
+          return createStringError(EC, Twine("Failed to open new cache file ") +
+                                           TempFile.TmpName + ": " +
+                                           EC.message() + "\n");
+        }
 
         // On POSIX systems, this will atomically replace the destination if
         // it already exists. We try to emulate this on Windows, but this may
@@ -114,11 +117,14 @@ Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
         // AddBuffer a copy of the bytes we wrote in that case. We do this
         // instead of just using the existing file, because the pruner might
         // delete the file before we get a chance to use it.
-        Error E = TempFile.keep(ObjectPathName);
+        E = TempFile.keep(ObjectPathName);
         E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
           std::error_code EC = E.convertToErrorCode();
           if (EC != errc::permission_denied)
-            return errorCodeToError(EC);
+            return createStringError(
+                EC, Twine("Failed to rename temporary file ") +
+                        TempFile.TmpName + " to " + ObjectPathName + ": " +
+                        EC.message() + "\n");
 
           auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
                                                        ObjectPathName);
@@ -131,11 +137,10 @@ Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
         });
 
         if (E)
-          report_fatal_error(Twine("Failed to rename temporary file ") +
-                             TempFile.TmpName + " to " + ObjectPathName + ": " +
-                             toString(std::move(E)) + "\n");
+          return E;
 
         AddBuffer(Task, ModuleName, std::move(*MBOrErr));
+        return Error::success();
       }
     };
 

llvm/tools/gold/gold-plugin.cpp

@@ -1119,7 +1119,9 @@ static std::vector<std::pair<SmallString<128>, bool>> runLTO() {
 
   auto AddBuffer = [&](size_t Task, const Twine &moduleName,
                        std::unique_ptr<MemoryBuffer> MB) {
-    *AddStream(Task, moduleName)->OS << MB->getBuffer();
+    auto Stream = *AddStream(Task, ModuleName);
+    Stream->OS << MB->getBuffer();
+    check(Stream->commit(), "Failed to commit cache");
   };
 
   FileCache Cache;

llvm/tools/llvm-lto2/llvm-lto2.cpp

@@ -448,7 +448,9 @@ static int run(int argc, char **argv) {
 
   auto AddBuffer = [&](size_t Task, const Twine &ModuleName,
                        std::unique_ptr<MemoryBuffer> MB) {
-    *AddStream(Task, ModuleName)->OS << MB->getBuffer();
+    auto Stream = AddStream(Task, ModuleName);
+    *Stream->OS << MB->getBuffer();
+    check(Stream->commit(), "Failed to commit cache");
   };
 
   FileCache Cache;

llvm/unittests/Support/CMakeLists.txt

@@ -18,6 +18,7 @@ add_llvm_unittest(SupportTests
   BranchProbabilityTest.cpp
   CachePruningTest.cpp
   CrashRecoveryTest.cpp
+  Caching.cpp
   Casting.cpp
   CheckedArithmeticTest.cpp
   Chrono.cpp

llvm/unittests/Support/Caching.cpp

@@ -0,0 +1,163 @@
+//===- Caching.cpp --------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Caching.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Testing/Support/Error.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+#define ASSERT_NO_ERROR(x)                                                     \
+  if (std::error_code ASSERT_NO_ERROR_ec = x) {                                \
+    SmallString<128> MessageStorage;                                           \
+    raw_svector_ostream Message(MessageStorage);                               \
+    Message << #x ": did not return errc::success.\n"                          \
+            << "error number: " << ASSERT_NO_ERROR_ec.value() << "\n"          \
+            << "error message: " << ASSERT_NO_ERROR_ec.message() << "\n";      \
+    GTEST_FATAL_FAILURE_(MessageStorage.c_str());                              \
+  } else {                                                                     \
+  }
+
+char data[] = "some data";
+
+TEST(Caching, Normal) {
+  SmallString<256> TempDir;
+  sys::path::system_temp_directory(true, TempDir);
+  SmallString<256> CacheDir;
+  sys::path::append(CacheDir, TempDir, "llvm_test_cache");
+
+  sys::fs::remove_directories(CacheDir.str());
+
+  std::unique_ptr<MemoryBuffer> CachedBuffer;
+  auto AddBuffer = [&CachedBuffer](unsigned Task, const Twine &ModuleName,
+                                   std::unique_ptr<MemoryBuffer> M) {
+    CachedBuffer = std::move(M);
+  };
+  auto CacheOrErr =
+      localCache("LLVMTestCache", "LLVMTest", CacheDir, AddBuffer);
+  ASSERT_TRUE(bool(CacheOrErr));
+
+  FileCache &Cache = *CacheOrErr;
+
+  {
+    auto AddStreamOrErr = Cache(1, "foo", "");
+    ASSERT_TRUE(bool(AddStreamOrErr));
+
+    AddStreamFn &AddStream = *AddStreamOrErr;
+    ASSERT_TRUE(AddStream);
+
+    auto FileOrErr = AddStream(1, "");
+    ASSERT_TRUE(bool(FileOrErr));
+
+    CachedFileStream *CFS = FileOrErr->get();
+    (*CFS->OS).write(data, sizeof(data));
+    ASSERT_THAT_ERROR(CFS->commit(), Succeeded());
+  }
+
+  {
+    auto AddStreamOrErr = Cache(1, "foo", "");
+    ASSERT_TRUE(bool(AddStreamOrErr));
+
+    AddStreamFn &AddStream = *AddStreamOrErr;
+    ASSERT_FALSE(AddStream);
+
+    ASSERT_TRUE(CachedBuffer->getBufferSize() == sizeof(data));
+    StringRef readData = CachedBuffer->getBuffer();
+    ASSERT_TRUE(memcmp(data, readData.data(), sizeof(data)) == 0);
+  }
+
+  ASSERT_NO_ERROR(sys::fs::remove_directories(CacheDir.str()));
+}
+
+TEST(Caching, WriteAfterCommit) {
+  SmallString<256> TempDir;
+  sys::path::system_temp_directory(true, TempDir);
+  SmallString<256> CacheDir;
+  sys::path::append(CacheDir, TempDir, "llvm_test_cache");
+
+  sys::fs::remove_directories(CacheDir.str());
+
+  std::unique_ptr<MemoryBuffer> CachedBuffer;
+  auto AddBuffer = [&CachedBuffer](unsigned Task, const Twine &ModuleName,
+                                   std::unique_ptr<MemoryBuffer> M) {
+    CachedBuffer = std::move(M);
+  };
+  auto CacheOrErr =
+      localCache("LLVMTestCache", "LLVMTest", CacheDir, AddBuffer);
+  ASSERT_TRUE(bool(CacheOrErr));
+
+  FileCache &Cache = *CacheOrErr;
+
+  auto AddStreamOrErr = Cache(1, "foo", "");
+  ASSERT_TRUE(bool(AddStreamOrErr));
+
+  AddStreamFn &AddStream = *AddStreamOrErr;
+  ASSERT_TRUE(AddStream);
+
+  auto FileOrErr = AddStream(1, "");
+  ASSERT_TRUE(bool(FileOrErr));
+
+  CachedFileStream *CFS = FileOrErr->get();
+  (*CFS->OS).write(data, sizeof(data));
+  ASSERT_THAT_ERROR(CFS->commit(), Succeeded());
+
+  EXPECT_DEATH(
+      { (*CFS->OS).write(data, sizeof(data)); }, "")
+      << "Write after commit did not cause abort";
+
+  ASSERT_NO_ERROR(sys::fs::remove_directories(CacheDir.str()));
+}
+
+TEST(Caching, NoCommit) {
+  SmallString<256> TempDir;
+  sys::path::system_temp_directory(true, TempDir);
+  SmallString<256> CacheDir;
+  sys::path::append(CacheDir, TempDir, "llvm_test_cache");
+
+  sys::fs::remove_directories(CacheDir.str());
+
+  std::unique_ptr<MemoryBuffer> CachedBuffer;
+  auto AddBuffer = [&CachedBuffer](unsigned Task, const Twine &ModuleName,
+                                   std::unique_ptr<MemoryBuffer> M) {
+    CachedBuffer = std::move(M);
+  };
+  auto CacheOrErr =
+      localCache("LLVMTestCache", "LLVMTest", CacheDir, AddBuffer);
+  ASSERT_TRUE(bool(CacheOrErr));
+
+  FileCache &Cache = *CacheOrErr;
+
+  auto AddStreamOrErr = Cache(1, "foo", "");
+  ASSERT_TRUE(bool(AddStreamOrErr));
+
+  AddStreamFn &AddStream = *AddStreamOrErr;
+  ASSERT_TRUE(AddStream);
+
+  auto FileOrErr = AddStream(1, "");
+  ASSERT_TRUE(bool(FileOrErr));
+
+  CachedFileStream *CFS = FileOrErr->get();
+  (*CFS->OS).write(data, sizeof(data));
+  ASSERT_THAT_ERROR(CFS->commit(), Succeeded());
+
+  EXPECT_DEATH(
+      {
+        auto FileOrErr = AddStream(1, "");
+        ASSERT_TRUE(bool(FileOrErr));
+
+        CachedFileStream *CFS = FileOrErr->get();
+        (*CFS->OS).write(data, sizeof(data));
+      },
+      "")
+      << "destruction without commit did not cause error";
+
+  ASSERT_NO_ERROR(sys::fs::remove_directories(CacheDir.str()));
+}