llvm/lib/Support/Caching.cpp

   1 //===-Caching.cpp - LLVM Local File Cache ---------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the localCache function, which simplifies creating,
  10 // adding to, and querying a local file system cache. localCache takes care of
  11 // periodically pruning older files from the cache using a CachePruningPolicy.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Support/Caching.h"
  16 #include "llvm/Support/Errc.h"
  17 #include "llvm/Support/FileSystem.h"
  18 #include "llvm/Support/MemoryBuffer.h"
  19 #include "llvm/Support/Path.h"
  20
  21 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  22 #include <unistd.h>
  23 #else
  24 #include <io.h>
  25 #endif
  26
  27 using namespace llvm;
  28
  29 Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
  30                                      const Twine &TempFilePrefixRef,
  31                                      const Twine &CacheDirectoryPathRef,
  32                                      AddBufferFn AddBuffer) {
  33
  34   // Create local copies which are safely captured-by-copy in lambdas
  35   SmallString<64> CacheName, TempFilePrefix, CacheDirectoryPath;
  36   CacheNameRef.toVector(CacheName);
  37   TempFilePrefixRef.toVector(TempFilePrefix);
  38   CacheDirectoryPathRef.toVector(CacheDirectoryPath);
  39
  40   return [=](unsigned Task, StringRef Key,
  41              const Twine &ModuleName) -> Expected<AddStreamFn> {
  42     // This choice of file name allows the cache to be pruned (see pruneCache()
  43     // in include/llvm/Support/CachePruning.h).
  44     SmallString<64> EntryPath;
  45     sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
  46     // First, see if we have a cache hit.
  47     SmallString<64> ResultPath;
  48     Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
  49         Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
  50     std::error_code EC;
  51     if (FDOrErr) {
  52       ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  53           MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
  54                                     /*FileSize=*/-1,
  55                                     /*RequiresNullTerminator=*/false);
  56       sys::fs::closeFile(*FDOrErr);
  57       if (MBOrErr) {
  58         AddBuffer(Task, ModuleName, std::move(*MBOrErr));
  59         return AddStreamFn();
  60       }
  61       EC = MBOrErr.getError();
  62     } else {
  63       EC = errorToErrorCode(FDOrErr.takeError());
  64     }
  65
  66     // On Windows we can fail to open a cache file with a permission denied
  67     // error. This generally means that another process has requested to delete
  68     // the file while it is still open, but it could also mean that another
  69     // process has opened the file without the sharing permissions we need.
  70     // Since the file is probably being deleted we handle it in the same way as
  71     // if the file did not exist at all.
  72     if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
  73       return createStringError(EC, Twine("Failed to open cache file ") +
  74                                        EntryPath + ": " + EC.message() + "\n");
  75
  76     // This file stream is responsible for commiting the resulting file to the
  77     // cache and calling AddBuffer to add it to the link.
  78     struct CacheStream : CachedFileStream {
  79       AddBufferFn AddBuffer;
  80       sys::fs::TempFile TempFile;
  81       std::string ModuleName;
  82       unsigned Task;
  83
  84       CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
  85                   sys::fs::TempFile TempFile, std::string EntryPath,
  86                   std::string ModuleName, unsigned Task)
  87           : CachedFileStream(std::move(OS), std::move(EntryPath)),
  88             AddBuffer(std::move(AddBuffer)), TempFile(std::move(TempFile)),
  89             ModuleName(ModuleName), Task(Task) {}
  90
  91       ~CacheStream() {
  92         // TODO: Manually commit rather than using non-trivial destructor,
  93         // allowing to replace report_fatal_errors with a return Error.
  94
  95         // Make sure the stream is closed before committing it.
  96         OS.reset();
  97
  98         // Open the file first to avoid racing with a cache pruner.
  99         ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
 100             MemoryBuffer::getOpenFile(
 101                 sys::fs::convertFDToNativeFile(TempFile.FD), ObjectPathName,
 102                 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
 103         if (!MBOrErr)
 104           report_fatal_error(Twine("Failed to open new cache file ") +
 105                              TempFile.TmpName + ": " +
 106                              MBOrErr.getError().message() + "\n");
 107
 108         // On POSIX systems, this will atomically replace the destination if
 109         // it already exists. We try to emulate this on Windows, but this may
 110         // fail with a permission denied error (for example, if the destination
 111         // is currently opened by another process that does not give us the
 112         // sharing permissions we need). Since the existing file should be
 113         // semantically equivalent to the one we are trying to write, we give
 114         // AddBuffer a copy of the bytes we wrote in that case. We do this
 115         // instead of just using the existing file, because the pruner might
 116         // delete the file before we get a chance to use it.
 117         Error E = TempFile.keep(ObjectPathName);
 118         E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
 119           std::error_code EC = E.convertToErrorCode();
 120           if (EC != errc::permission_denied)
 121             return errorCodeToError(EC);
 122
 123           auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
 124                                                        ObjectPathName);
 125           MBOrErr = std::move(MBCopy);
 126
 127           // FIXME: should we consume the discard error?
 128           consumeError(TempFile.discard());
 129
 130           return Error::success();
 131         });
 132
 133         if (E)
 134           report_fatal_error(Twine("Failed to rename temporary file ") +
 135                              TempFile.TmpName + " to " + ObjectPathName + ": " +
 136                              toString(std::move(E)) + "\n");
 137
 138         AddBuffer(Task, ModuleName, std::move(*MBOrErr));
 139       }
 140     };
 141
 142     return [=](size_t Task, const Twine &ModuleName)
 143                -> Expected<std::unique_ptr<CachedFileStream>> {
 144       // Create the cache directory if not already done. Doing this lazily
 145       // ensures the filesystem isn't mutated until the cache is.
 146       if (std::error_code EC = sys::fs::create_directories(
 147               CacheDirectoryPath, /*IgnoreExisting=*/true))
 148         return createStringError(EC, Twine("can't create cache directory ") +
 149                                          CacheDirectoryPath + ": " +
 150                                          EC.message());
 151
 152       // Write to a temporary to avoid race condition
 153       SmallString<64> TempFilenameModel;
 154       sys::path::append(TempFilenameModel, CacheDirectoryPath,
 155                         TempFilePrefix + "-%%%%%%.tmp.o");
 156       Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
 157           TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
 158       if (!Temp)
 159         return createStringError(errc::io_error,
 160                                  toString(Temp.takeError()) + ": " + CacheName +
 161                                      ": Can't get a temporary file");
 162
 163       // This CacheStream will move the temporary file into the cache when done.
 164       return std::make_unique<CacheStream>(
 165           std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
 166           AddBuffer, std::move(*Temp), std::string(EntryPath), ModuleName.str(),
 167           Task);
 168     };
 169   };
 170 }