77 lines
2.8 KiB
C++
77 lines
2.8 KiB
C++
//===- Filesystem.cpp -----------------------------------------------------===//
|
|
//
|
|
// The LLVM Linker
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file contains a few utility functions to handle files.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "Filesystem.h"
|
|
#include "Config.h"
|
|
#include "llvm/Support/FileSystem.h"
|
|
#include "llvm/Support/FileOutputBuffer.h"
|
|
#include <thread>
|
|
|
|
using namespace llvm;
|
|
|
|
using namespace lld;
|
|
using namespace lld::elf;
|
|
|
|
// Removes a given file asynchronously. This is a performance hack,
|
|
// so remove this when operating systems are improved.
|
|
//
|
|
// On Linux (and probably on other Unix-like systems), unlink(2) is a
|
|
// noticeably slow system call. As of 2016, unlink takes 250
|
|
// milliseconds to remove a 1 GB file on ext4 filesystem on my machine.
|
|
//
|
|
// To create a new result file, we first remove existing file. So, if
|
|
// you repeatedly link a 1 GB program in a regular compile-link-debug
|
|
// cycle, every cycle wastes 250 milliseconds only to remove a file.
|
|
// Since LLD can link a 1 GB binary in about 5 seconds, that waste
|
|
// actually counts.
|
|
//
|
|
// This function spawns a background thread to call unlink.
|
|
// The calling thread returns almost immediately.
|
|
void elf::unlinkAsync(StringRef Path) {
|
|
if (!Config->Threads || !sys::fs::exists(Config->OutputFile))
|
|
return;
|
|
|
|
// First, rename Path to avoid race condition. We cannot remove
|
|
// Path from a different thread because we are now going to create
|
|
// Path as a new file. If we do that in a different thread, the new
|
|
// thread can remove the new file.
|
|
SmallString<128> TempPath;
|
|
if (sys::fs::createUniqueFile(Path + "tmp%%%%%%%%", TempPath))
|
|
return;
|
|
if (sys::fs::rename(Path, TempPath)) {
|
|
sys::fs::remove(TempPath);
|
|
return;
|
|
}
|
|
|
|
// Remove TempPath in background.
|
|
std::thread([=] { ::remove(TempPath.str().str().c_str()); }).detach();
|
|
}
|
|
|
|
// Simulate file creation to see if Path is writable.
|
|
//
|
|
// Determining whether a file is writable or not is amazingly hard,
|
|
// and after all the only reliable way of doing that is to actually
|
|
// create a file. But we don't want to do that in this function
|
|
// because LLD shouldn't update any file if it will end in a failure.
|
|
// We also don't want to reimplement heuristics to determine if a
|
|
// file is writable. So we'll let FileOutputBuffer do the work.
|
|
//
|
|
// FileOutputBuffer doesn't touch a desitnation file until commit()
|
|
// is called. We use that class without calling commit() to predict
|
|
// if the given file is writable.
|
|
std::error_code elf::tryCreateFile(StringRef Path) {
|
|
if (Path.empty())
|
|
return std::error_code();
|
|
return FileOutputBuffer::create(Path, 1).getError();
|
|
}
|