From 95fa4005f5aa99878c4053e95b230f0b8b6a4d6d Mon Sep 17 00:00:00 2001 From: Douglas Gregor Date: Sun, 29 Jan 2012 20:15:10 +0000 Subject: [PATCH] Move Clang's file-level locking facility over to LLVM's support library, since it doesn't really have anything to do with Clang. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149203 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/Support/LockFileManager.h | 74 +++++++++ lib/Support/CMakeLists.txt | 1 + lib/Support/LockFileManager.cpp | 216 +++++++++++++++++++++++++ 3 files changed, 291 insertions(+) create mode 100644 include/llvm/Support/LockFileManager.h create mode 100644 lib/Support/LockFileManager.cpp diff --git a/include/llvm/Support/LockFileManager.h b/include/llvm/Support/LockFileManager.h new file mode 100644 index 00000000000..e2fa8ebc56e --- /dev/null +++ b/include/llvm/Support/LockFileManager.h @@ -0,0 +1,74 @@ +//===--- LockFileManager.h - File-level locking utility ---------*- C++ -*-===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +#ifndef LLVM_SUPPORT_LOCKFILEMANAGER_H +#define LLVM_SUPPORT_LOCKFILEMANAGER_H + +#include "llvm/ADT/Optional.h" +#include "llvm/ADT/SmallString.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/Support/system_error.h" +#include // for std::pair + +namespace llvm { + +/// \brief Class that manages the creation of a lock file to aid +/// implicit coordination between different processes. +/// +/// The implicit coordination works by creating a ".lock" file alongside +/// the file that we're coordinating for, using the atomicity of the file +/// system to ensure that only a single process can create that ".lock" file. +/// When the lock file is removed, the owning process has finished the +/// operation. +class LockFileManager { +public: + /// \brief Describes the state of a lock file. + enum LockFileState { + /// \brief The lock file has been created and is owned by this instance + /// of the object. + LFS_Owned, + /// \brief The lock file already exists and is owned by some other + /// instance. + LFS_Shared, + /// \brief An error occurred while trying to create or find the lock + /// file. + LFS_Error + }; + +private: + SmallString<128> LockFileName; + SmallString<128> UniqueLockFileName; + + Optional > Owner; + Optional Error; + + LockFileManager(const LockFileManager &); + LockFileManager &operator=(const LockFileManager &); + + static Optional > + readLockFile(StringRef LockFileName); + + static bool processStillExecuting(StringRef Hostname, int PID); + +public: + + LockFileManager(StringRef FileName); + ~LockFileManager(); + + /// \brief Determine the state of the lock file. + LockFileState getState() const; + + operator LockFileState() const { return getState(); } + + /// \brief For a shared lock, wait until the owner releases the lock. + void waitForUnlock(); +}; + +} // end namespace llvm + +#endif // LLVM_SUPPORT_LOCKFILEMANAGER_H diff --git a/lib/Support/CMakeLists.txt b/lib/Support/CMakeLists.txt index 7bb5cb4ea87..322d32f876f 100644 --- a/lib/Support/CMakeLists.txt +++ b/lib/Support/CMakeLists.txt @@ -31,6 +31,7 @@ add_llvm_library(LLVMSupport IsInf.cpp IsNAN.cpp JSONParser.cpp + LockFileManager.cpp ManagedStatic.cpp MemoryBuffer.cpp MemoryObject.cpp diff --git a/lib/Support/LockFileManager.cpp b/lib/Support/LockFileManager.cpp new file mode 100644 index 00000000000..64404a1a8e7 --- /dev/null +++ b/lib/Support/LockFileManager.cpp @@ -0,0 +1,216 @@ +//===--- LockFileManager.cpp - File-level Locking Utility------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +#include "llvm/Support/LockFileManager.h" +#include "llvm/Support/FileSystem.h" +#include "llvm/Support/raw_ostream.h" +#include +#include +#include +#if LLVM_ON_WIN32 +#include +#endif +#if LLVM_ON_UNIX +#include +#endif +using namespace llvm; + +/// \brief Attempt to read the lock file with the given name, if it exists. +/// +/// \param LockFileName The name of the lock file to read. +/// +/// \returns The process ID of the process that owns this lock file +Optional > +LockFileManager::readLockFile(StringRef LockFileName) { + // Check whether the lock file exists. If not, clearly there's nothing + // to read, so we just return. + bool Exists = false; + if (sys::fs::exists(LockFileName, Exists) || !Exists) + return Optional >(); + + // Read the owning host and PID out of the lock file. If it appears that the + // owning process is dead, the lock file is invalid. + int PID = 0; + std::string Hostname; + std::ifstream Input(LockFileName.str().c_str()); + if (Input >> Hostname >> PID && PID > 0 && + processStillExecuting(Hostname, PID)) + return std::make_pair(Hostname, PID); + + // Delete the lock file. It's invalid anyway. + bool Existed; + sys::fs::remove(LockFileName, Existed); + return Optional >(); +} + +bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) { +#if LLVM_ON_UNIX + char MyHostname[256]; + MyHostname[255] = 0; + MyHostname[0] = 0; + gethostname(MyHostname, 255); + // Check whether the process is dead. If so, we're done. + if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH) + return false; +#endif + + return true; +} + +LockFileManager::LockFileManager(StringRef FileName) +{ + LockFileName = FileName; + LockFileName += ".lock"; + + // If the lock file already exists, don't bother to try to create our own + // lock file; it won't work anyway. Just figure out who owns this lock file. + if ((Owner = readLockFile(LockFileName))) + return; + + // Create a lock file that is unique to this instance. + UniqueLockFileName = LockFileName; + UniqueLockFileName += "-%%%%%%%%"; + int UniqueLockFileID; + if (error_code EC + = sys::fs::unique_file(UniqueLockFileName.str(), + UniqueLockFileID, + UniqueLockFileName, + /*makeAbsolute=*/false)) { + Error = EC; + return; + } + + // Write our process ID to our unique lock file. + { + raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true); + +#if LLVM_ON_UNIX + // FIXME: move getpid() call into LLVM + char hostname[256]; + hostname[255] = 0; + hostname[0] = 0; + gethostname(hostname, 255); + Out << hostname << ' ' << getpid(); +#else + Out << "localhost 1"; +#endif + Out.close(); + + if (Out.has_error()) { + // We failed to write out PID, so make up an excuse, remove the + // unique lock file, and fail. + Error = make_error_code(errc::no_space_on_device); + bool Existed; + sys::fs::remove(UniqueLockFileName.c_str(), Existed); + return; + } + } + + // Create a hard link from the lock file name. If this succeeds, we're done. + error_code EC + = sys::fs::create_hard_link(UniqueLockFileName.str(), + LockFileName.str()); + if (EC == errc::success) + return; + + // Creating the hard link failed. + +#ifdef LLVM_ON_UNIX + // The creation of the hard link may appear to fail, but if stat'ing the + // unique file returns a link count of 2, then we can still declare success. + struct stat StatBuf; + if (stat(UniqueLockFileName.c_str(), &StatBuf) == 0 && + StatBuf.st_nlink == 2) + return; +#endif + + // Someone else managed to create the lock file first. Wipe out our unique + // lock file (it's useless now) and read the process ID from the lock file. + bool Existed; + sys::fs::remove(UniqueLockFileName.str(), Existed); + if ((Owner = readLockFile(LockFileName))) + return; + + // There is a lock file that nobody owns; try to clean it up and report + // an error. + sys::fs::remove(LockFileName.str(), Existed); + Error = EC; +} + +LockFileManager::LockFileState LockFileManager::getState() const { + if (Owner) + return LFS_Shared; + + if (Error) + return LFS_Error; + + return LFS_Owned; +} + +LockFileManager::~LockFileManager() { + if (getState() != LFS_Owned) + return; + + // Since we own the lock, remove the lock file and our own unique lock file. + bool Existed; + sys::fs::remove(LockFileName.str(), Existed); + sys::fs::remove(UniqueLockFileName.str(), Existed); +} + +void LockFileManager::waitForUnlock() { + if (getState() != LFS_Shared) + return; + +#if LLVM_ON_WIN32 + unsigned long Interval = 1; +#else + struct timespec Interval; + Interval.tv_sec = 0; + Interval.tv_nsec = 1000000; +#endif + // Don't wait more than an hour for the file to appear. + const unsigned MaxSeconds = 3600; + do { + // Sleep for the designated interval, to allow the owning process time to + // finish up and remove the lock file. + // FIXME: Should we hook in to system APIs to get a notification when the + // lock file is deleted? +#if LLVM_ON_WIN32 + Sleep(Interval); +#else + nanosleep(&Interval, NULL); +#endif + // If the file no longer exists, we're done. + bool Exists = false; + if (!sys::fs::exists(LockFileName.str(), Exists) && !Exists) + return; + + if (!processStillExecuting((*Owner).first, (*Owner).second)) + return; + + // Exponentially increase the time we wait for the lock to be removed. +#if LLVM_ON_WIN32 + Interval *= 2; +#else + Interval.tv_sec *= 2; + Interval.tv_nsec *= 2; + if (Interval.tv_nsec >= 1000000000) { + ++Interval.tv_sec; + Interval.tv_nsec -= 1000000000; + } +#endif + } while ( +#if LLVM_ON_WIN32 + Interval < MaxSeconds * 1000 +#else + Interval.tv_sec < (time_t)MaxSeconds +#endif + ); + + // Give up. +}