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//===--- FileCache.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 "support/FileCache.h"
namespace clang {
namespace clangd {
// Sentinel values for the Size cache key. In both cases, a successful stat of
// the file will never result in the cached value being reused.
// The cached value does not reflect the current content on disk.
static constexpr uint64_t CacheDiskMismatch =
std::numeric_limits<uint64_t>::max();
// The cached value reflects that the file doesn't exist.
static constexpr uint64_t FileNotFound = CacheDiskMismatch - 1;
FileCache::FileCache(llvm::StringRef Path)
: Path(Path), ValidTime(std::chrono::steady_clock::time_point::min()),
ModifiedTime(), Size(CacheDiskMismatch) {
assert(llvm::sys::path::is_absolute(Path));
}
void FileCache::read(
const ThreadsafeFS &TFS, std::chrono::steady_clock::time_point FreshTime,
llvm::function_ref<void(llvm::Optional<llvm::StringRef>)> Parse,
llvm::function_ref<void()> Read) const {
std::lock_guard<std::mutex> Lock(Mu);
// We're going to update the cache and return whatever's in it.
auto Return = llvm::make_scope_exit(Read);
// Return any sufficiently recent result without doing any further work.
if (ValidTime > FreshTime)
return;
// Ensure we always bump ValidTime, so that FreshTime imposes a hard limit on
// how often we do IO.
auto BumpValidTime = llvm::make_scope_exit(
[&] { ValidTime = std::chrono::steady_clock::now(); });
// stat is cheaper than opening the file. It's usually unchanged.
assert(llvm::sys::path::is_absolute(Path));
auto FS = TFS.view(/*CWD=*/llvm::None);
auto Stat = FS->status(Path);
if (!Stat || !Stat->isRegularFile()) {
if (Size != FileNotFound) // Allow "not found" value to be cached.
Parse(llvm::None);
// Ensure the cache key won't match any future stat().
Size = FileNotFound;
return;
}
// If the modified-time and size match, assume the content does too.
if (Size == Stat->getSize() &&
ModifiedTime == Stat->getLastModificationTime())
return;
// OK, the file has actually changed. Update cache key, compute new value.
Size = Stat->getSize();
ModifiedTime = Stat->getLastModificationTime();
// Now read the file from disk.
if (auto Buf = FS->getBufferForFile(Path)) {
Parse(Buf->get()->getBuffer());
// Result is cacheable if the actual read size matches the new cache key.
// (We can't update the cache key, because we don't know the new mtime).
if (Buf->get()->getBufferSize() != Size)
Size = CacheDiskMismatch;
} else {
// File was unreadable. Keep the old value and try again next time.
Size = CacheDiskMismatch;
}
}
} // namespace clangd
} // namespace clang
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