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LevelDB-Time-To-Live
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LevelDB-Time-To-Live/util/env_posix.cc

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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include <atomic>
#include <cstring>
#include <deque>
#include <limits>
#include <set>
#include "leveldb/env.h"
#include "leveldb/slice.h"
#include "port/port.h"
#include "port/thread_annotations.h"
#include "util/logging.h"
#include "util/mutexlock.h"
#include "util/posix_logger.h"
#include "util/env_posix_test_helper.h"
// HAVE_FDATASYNC is defined in the auto-generated port_config.h, which is
// included by port_stdcxx.h.
#if !HAVE_FDATASYNC
#define fdatasync fsync
#endif // !HAVE_FDATASYNC
namespace leveldb {
namespace {
static int open_read_only_file_limit = -1;
static int mmap_limit = -1;
constexpr const size_t kWritableFileBufferSize = 65536;
static Status PosixError(const std::string& context, int err_number) {
if (err_number == ENOENT) {
return Status::NotFound(context, strerror(err_number));
} else {
return Status::IOError(context, strerror(err_number));
}
}
// Helper class to limit resource usage to avoid exhaustion.
// Currently used to limit read-only file descriptors and mmap file usage
// so that we do not run out of file descriptors or virtual memory, or run into
// kernel performance problems for very large databases.
class Limiter {
public:
// Limit maximum number of resources to |max_acquires|.
Limiter(int max_acquires) : acquires_allowed_(max_acquires) {}
Limiter(const Limiter&) = delete;
Limiter operator=(const Limiter&) = delete;
// If another resource is available, acquire it and return true.
// Else return false.
bool Acquire() {
int old_acquires_allowed =
acquires_allowed_.fetch_sub(1, std::memory_order_relaxed);
if (old_acquires_allowed > 0)
return true;
acquires_allowed_.fetch_add(1, std::memory_order_relaxed);
return false;
}
// Release a resource acquired by a previous call to Acquire() that returned
// true.
void Release() {
acquires_allowed_.fetch_add(1, std::memory_order_relaxed);
}
private:
// The number of available resources.
//
// This is a counter and is not tied to the invariants of any other class, so
// it can be operated on safely using std::memory_order_relaxed.
std::atomic<int> acquires_allowed_;
};
class PosixSequentialFile: public SequentialFile {
private:
std::string filename_;
int fd_;
public:
PosixSequentialFile(const std::string& fname, int fd)
: filename_(fname), fd_(fd) {}
virtual ~PosixSequentialFile() { close(fd_); }
virtual Status Read(size_t n, Slice* result, char* scratch) {
Status s;
while (true) {
ssize_t r = read(fd_, scratch, n);
if (r < 0) {
if (errno == EINTR) {
continue; // Retry
}
s = PosixError(filename_, errno);
break;
}
*result = Slice(scratch, r);
break;
}
return s;
}
virtual Status Skip(uint64_t n) {
if (lseek(fd_, n, SEEK_CUR) == static_cast<off_t>(-1)) {
return PosixError(filename_, errno);
}
return Status::OK();
}
};
// pread() based random-access
class PosixRandomAccessFile: public RandomAccessFile {
private:
std::string filename_;
bool temporary_fd_; // If true, fd_ is -1 and we open on every read.
int fd_;
Limiter* limiter_;
public:
PosixRandomAccessFile(const std::string& fname, int fd, Limiter* limiter)
: filename_(fname), fd_(fd), limiter_(limiter) {
temporary_fd_ = !limiter->Acquire();
if (temporary_fd_) {
// Open file on every access.
close(fd_);
fd_ = -1;
}
}
virtual ~PosixRandomAccessFile() {
if (!temporary_fd_) {
close(fd_);
limiter_->Release();
}
}
virtual Status Read(uint64_t offset, size_t n, Slice* result,
char* scratch) const {
int fd = fd_;
if (temporary_fd_) {
fd = open(filename_.c_str(), O_RDONLY);
if (fd < 0) {
return PosixError(filename_, errno);
}
}
Status s;
ssize_t r = pread(fd, scratch, n, static_cast<off_t>(offset));
*result = Slice(scratch, (r < 0) ? 0 : r);
if (r < 0) {
// An error: return a non-ok status
s = PosixError(filename_, errno);
}
if (temporary_fd_) {
// Close the temporary file descriptor opened earlier.
close(fd);
}
return s;
}
};
// mmap() based random-access
class PosixMmapReadableFile: public RandomAccessFile {
private:
std::string filename_;
void* mmapped_region_;
size_t length_;
Limiter* limiter_;
public:
// base[0,length-1] contains the mmapped contents of the file.
PosixMmapReadableFile(const std::string& fname, void* base, size_t length,
Limiter* limiter)
: filename_(fname), mmapped_region_(base), length_(length),
limiter_(limiter) {
}
virtual ~PosixMmapReadableFile() {
munmap(mmapped_region_, length_);
limiter_->Release();
}
virtual Status Read(uint64_t offset, size_t n, Slice* result,
char* scratch) const {
Status s;
if (offset + n > length_) {
*result = Slice();
s = PosixError(filename_, EINVAL);
} else {
*result = Slice(reinterpret_cast<char*>(mmapped_region_) + offset, n);
}
return s;
}
};
class PosixWritableFile final : public WritableFile {
public:
PosixWritableFile(std::string filename, int fd)
: pos_(0), fd_(fd), is_manifest_(IsManifest(filename)),
filename_(std::move(filename)), dirname_(Dirname(filename_)) {}
~PosixWritableFile() override {
if (fd_ >= 0) {
// Ignoring any potential errors
Close();
}
}
Status Append(const Slice& data) override {
size_t write_size = data.size();
const char* write_data = data.data();
// Fit as much as possible into buffer.
size_t copy_size = std::min(write_size, kWritableFileBufferSize - pos_);
std::memcpy(buf_ + pos_, write_data, copy_size);
write_data += copy_size;
write_size -= copy_size;
pos_ += copy_size;
if (write_size == 0) {
return Status::OK();
}
// Can't fit in buffer, so need to do at least one write.
Status status = FlushBuffer();
if (!status.ok()) {
return status;
}
// Small writes go to buffer, large writes are written directly.
if (write_size < kWritableFileBufferSize) {
std::memcpy(buf_, write_data, write_size);
pos_ = write_size;
return Status::OK();
}
return WriteUnbuffered(write_data, write_size);
}
Status Close() override {
Status status = FlushBuffer();
const int close_result = ::close(fd_);
if (close_result < 0 && status.ok()) {
status = PosixError(filename_, errno);
}
fd_ = -1;
return status;
}
Status Flush() override {
return FlushBuffer();
}
Status Sync() override {
// Ensure new files referred to by the manifest are in the filesystem.
//
// This needs to happen before the manifest file is flushed to disk, to
// avoid crashing in a state where the manifest refers to files that are not
// yet on disk.
Status status = SyncDirIfManifest();
if (!status.ok()) {
return status;
}
status = FlushBuffer();
if (status.ok() && ::fdatasync(fd_) != 0) {
status = PosixError(filename_, errno);
}
return status;
}
private:
Status FlushBuffer() {
Status status = WriteUnbuffered(buf_, pos_);
pos_ = 0;
return status;
}
Status WriteUnbuffered(const char* data, size_t size) {
while (size > 0) {
ssize_t write_result = ::write(fd_, data, size);
if (write_result < 0) {
if (errno == EINTR) {
continue; // Retry
}
return PosixError(filename_, errno);
}
data += write_result;
size -= write_result;
}
return Status::OK();
}
Status SyncDirIfManifest() {
Status status;
if (!is_manifest_) {
return status;
}
int fd = ::open(dirname_.c_str(), O_RDONLY);
if (fd < 0) {
status = PosixError(dirname_, errno);
} else {
if (::fsync(fd) < 0) {
status = PosixError(dirname_, errno);
}
::close(fd);
}
return status;
}
// Returns the directory name in a path pointing to a file.
//
// Returns "." if the path does not contain any directory separator.
static std::string Dirname(const std::string& filename) {
std::string::size_type separator_pos = filename.rfind('/');
if (separator_pos == std::string::npos) {
return std::string(".");
}
// The filename component should not contain a path separator. If it does,
// the splitting was done incorrectly.
assert(filename.find('/', separator_pos + 1) == std::string::npos);
return filename.substr(0, separator_pos);
}
// Extracts the file name from a path pointing to a file.
//
// The returned Slice points to |filename|'s data buffer, so it is only valid
// while |filename| is alive and unchanged.
static Slice Basename(const std::string& filename) {
std::string::size_type separator_pos = filename.rfind('/');
if (separator_pos == std::string::npos) {
return Slice(filename);
}
// The filename component should not contain a path separator. If it does,
// the splitting was done incorrectly.
assert(filename.find('/', separator_pos + 1) == std::string::npos);
return Slice(filename.data() + separator_pos + 1,
filename.length() - separator_pos - 1);
}
// True if the given file is a manifest file.
static bool IsManifest(const std::string& filename) {
return Basename(filename).starts_with("MANIFEST");
}
// buf_[0, pos_ - 1] contains data to be written to fd_.
char buf_[kWritableFileBufferSize];
size_t pos_;
int fd_;
const bool is_manifest_; // True if the file's name starts with MANIFEST.
const std::string filename_;
const std::string dirname_; // The directory of filename_.
};
static int LockOrUnlock(int fd, bool lock) {
errno = 0;
struct flock f;
memset(&f, 0, sizeof(f));
f.l_type = (lock ? F_WRLCK : F_UNLCK);
f.l_whence = SEEK_SET;
f.l_start = 0;
f.l_len = 0; // Lock/unlock entire file
return fcntl(fd, F_SETLK, &f);
}
class PosixFileLock : public FileLock {
public:
int fd_;
std::string name_;
};
// Set of locked files. We keep a separate set instead of just
// relying on fcntrl(F_SETLK) since fcntl(F_SETLK) does not provide
// any protection against multiple uses from the same process.
class PosixLockTable {
private:
port::Mutex mu_;
std::set<std::string> locked_files_ GUARDED_BY(mu_);
public:
bool Insert(const std::string& fname) LOCKS_EXCLUDED(mu_) {
MutexLock l(&mu_);
return locked_files_.insert(fname).second;
}
void Remove(const std::string& fname) LOCKS_EXCLUDED(mu_) {
MutexLock l(&mu_);
locked_files_.erase(fname);
}
};
class PosixEnv : public Env {
public:
PosixEnv();
virtual ~PosixEnv() {
char msg[] = "Destroying Env::Default()\n";
fwrite(msg, 1, sizeof(msg), stderr);
abort();
}
virtual Status NewSequentialFile(const std::string& fname,
SequentialFile** result) {
int fd = open(fname.c_str(), O_RDONLY);
if (fd < 0) {
*result = nullptr;
return PosixError(fname, errno);
} else {
*result = new PosixSequentialFile(fname, fd);
return Status::OK();
}
}
virtual Status NewRandomAccessFile(const std::string& fname,
RandomAccessFile** result) {
*result = nullptr;
Status s;
int fd = open(fname.c_str(), O_RDONLY);
if (fd < 0) {
s = PosixError(fname, errno);
} else if (mmap_limit_.Acquire()) {
uint64_t size;
s = GetFileSize(fname, &size);
if (s.ok()) {
void* base = mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0);
if (base != MAP_FAILED) {
*result = new PosixMmapReadableFile(fname, base, size, &mmap_limit_);
} else {
s = PosixError(fname, errno);
}
}
close(fd);
if (!s.ok()) {
mmap_limit_.Release();
}
} else {
*result = new PosixRandomAccessFile(fname, fd, &fd_limit_);
}
return s;
}
virtual Status NewWritableFile(const std::string& fname,
WritableFile** result) {
Status s;
int fd = open(fname.c_str(), O_TRUNC | O_WRONLY | O_CREAT, 0644);
if (fd < 0) {
*result = nullptr;
s = PosixError(fname, errno);
} else {
*result = new PosixWritableFile(fname, fd);
}
return s;
}
virtual Status NewAppendableFile(const std::string& fname,
WritableFile** result) {
Status s;
int fd = open(fname.c_str(), O_APPEND | O_WRONLY | O_CREAT, 0644);
if (fd < 0) {
*result = nullptr;
s = PosixError(fname, errno);
} else {
*result = new PosixWritableFile(fname, fd);
}
return s;
}
virtual bool FileExists(const std::string& fname) {
return access(fname.c_str(), F_OK) == 0;
}
virtual Status GetChildren(const std::string& dir,
std::vector<std::string>* result) {
result->clear();
DIR* d = opendir(dir.c_str());
if (d == nullptr) {
return PosixError(dir, errno);
}
struct dirent* entry;
while ((entry = readdir(d)) != nullptr) {
result->push_back(entry->d_name);
}
closedir(d);
return Status::OK();
}
virtual Status DeleteFile(const std::string& fname) {
Status result;
if (unlink(fname.c_str()) != 0) {
result = PosixError(fname, errno);
}
return result;
}
virtual Status CreateDir(const std::string& name) {
Status result;
if (mkdir(name.c_str(), 0755) != 0) {
result = PosixError(name, errno);
}
return result;
}
virtual Status DeleteDir(const std::string& name) {
Status result;
if (rmdir(name.c_str()) != 0) {
result = PosixError(name, errno);
}
return result;
}
virtual Status GetFileSize(const std::string& fname, uint64_t* size) {
Status s;
struct stat sbuf;
if (stat(fname.c_str(), &sbuf) != 0) {
*size = 0;
s = PosixError(fname, errno);
} else {
*size = sbuf.st_size;
}
return s;
}
virtual Status RenameFile(const std::string& src, const std::string& target) {
Status result;
if (rename(src.c_str(), target.c_str()) != 0) {
result = PosixError(src, errno);
}
return result;
}
virtual Status LockFile(const std::string& fname, FileLock** lock) {
*lock = nullptr;
Status result;
int fd = open(fname.c_str(), O_RDWR | O_CREAT, 0644);
if (fd < 0) {
result = PosixError(fname, errno);
} else if (!locks_.Insert(fname)) {
close(fd);
result = Status::IOError("lock " + fname, "already held by process");
} else if (LockOrUnlock(fd, true) == -1) {
result = PosixError("lock " + fname, errno);
close(fd);
locks_.Remove(fname);
} else {
PosixFileLock* my_lock = new PosixFileLock;
my_lock->fd_ = fd;
my_lock->name_ = fname;
*lock = my_lock;
}
return result;
}
virtual Status UnlockFile(FileLock* lock) {
PosixFileLock* my_lock = reinterpret_cast<PosixFileLock*>(lock);
Status result;
if (LockOrUnlock(my_lock->fd_, false) == -1) {
result = PosixError("unlock", errno);
}
locks_.Remove(my_lock->name_);
close(my_lock->fd_);
delete my_lock;
return result;
}
virtual void Schedule(void (*function)(void*), void* arg);
virtual void StartThread(void (*function)(void* arg), void* arg);
virtual Status GetTestDirectory(std::string* result) {
const char* env = getenv("TEST_TMPDIR");
if (env && env[0] != '\0') {
*result = env;
} else {
char buf[100];
snprintf(buf, sizeof(buf), "/tmp/leveldbtest-%d", int(geteuid()));
*result = buf;
}
// Directory may already exist
CreateDir(*result);
return Status::OK();
}
static uint64_t gettid() {
pthread_t tid = pthread_self();
uint64_t thread_id = 0;
memcpy(&thread_id, &tid, std::min(sizeof(thread_id), sizeof(tid)));
return thread_id;
}
virtual Status NewLogger(const std::string& fname, Logger** result) {
FILE* f = fopen(fname.c_str(), "w");
if (f == nullptr) {
*result = nullptr;
return PosixError(fname, errno);
} else {
*result = new PosixLogger(f, &PosixEnv::gettid);
return Status::OK();
}
}
virtual uint64_t NowMicros() {
struct timeval tv;
gettimeofday(&tv, nullptr);
return static_cast<uint64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
}
virtual void SleepForMicroseconds(int micros) {
usleep(micros);
}
private:
void PthreadCall(const char* label, int result) {
if (result != 0) {
fprintf(stderr, "pthread %s: %s\n", label, strerror(result));
abort();
}
}
// BGThread() is the body of the background thread
void BGThread();
static void* BGThreadWrapper(void* arg) {
reinterpret_cast<PosixEnv*>(arg)->BGThread();
return nullptr;
}
pthread_mutex_t mu_;
pthread_cond_t bgsignal_;
pthread_t bgthread_;
bool started_bgthread_;
// Entry per Schedule() call
struct BGItem { void* arg; void (*function)(void*); };
typedef std::deque<BGItem> BGQueue;
BGQueue queue_;
PosixLockTable locks_;
Limiter mmap_limit_;
Limiter fd_limit_;
};
// Return the maximum number of concurrent mmaps.
static int MaxMmaps() {
if (mmap_limit >= 0) {
return mmap_limit;
}
// Up to 1000 mmaps for 64-bit binaries; none for smaller pointer sizes.
mmap_limit = sizeof(void*) >= 8 ? 1000 : 0;
return mmap_limit;
}
// Return the maximum number of read-only files to keep open.
static intptr_t MaxOpenFiles() {
if (open_read_only_file_limit >= 0) {
return open_read_only_file_limit;
}
struct rlimit rlim;
if (getrlimit(RLIMIT_NOFILE, &rlim)) {
// getrlimit failed, fallback to hard-coded default.
open_read_only_file_limit = 50;
} else if (rlim.rlim_cur == RLIM_INFINITY) {
open_read_only_file_limit = std::numeric_limits<int>::max();
} else {
// Allow use of 20% of available file descriptors for read-only files.
open_read_only_file_limit = rlim.rlim_cur / 5;
}
return open_read_only_file_limit;
}
PosixEnv::PosixEnv()
: started_bgthread_(false),
mmap_limit_(MaxMmaps()),
fd_limit_(MaxOpenFiles()) {
PthreadCall("mutex_init", pthread_mutex_init(&mu_, nullptr));
PthreadCall("cvar_init", pthread_cond_init(&bgsignal_, nullptr));
}
void PosixEnv::Schedule(void (*function)(void*), void* arg) {
PthreadCall("lock", pthread_mutex_lock(&mu_));
// Start background thread if necessary
if (!started_bgthread_) {
started_bgthread_ = true;
PthreadCall(
"create thread",
pthread_create(&bgthread_, nullptr, &PosixEnv::BGThreadWrapper, this));
}
// If the queue is currently empty, the background thread may currently be
// waiting.
if (queue_.empty()) {
PthreadCall("signal", pthread_cond_signal(&bgsignal_));
}
// Add to priority queue
queue_.push_back(BGItem());
queue_.back().function = function;
queue_.back().arg = arg;
PthreadCall("unlock", pthread_mutex_unlock(&mu_));
}
void PosixEnv::BGThread() {
while (true) {
// Wait until there is an item that is ready to run
PthreadCall("lock", pthread_mutex_lock(&mu_));
while (queue_.empty()) {
PthreadCall("wait", pthread_cond_wait(&bgsignal_, &mu_));
}
void (*function)(void*) = queue_.front().function;
void* arg = queue_.front().arg;
queue_.pop_front();
PthreadCall("unlock", pthread_mutex_unlock(&mu_));
(*function)(arg);
}
}
namespace {
struct StartThreadState {
void (*user_function)(void*);
void* arg;
};
}
static void* StartThreadWrapper(void* arg) {
StartThreadState* state = reinterpret_cast<StartThreadState*>(arg);
state->user_function(state->arg);
delete state;
return nullptr;
}
void PosixEnv::StartThread(void (*function)(void* arg), void* arg) {
pthread_t t;
StartThreadState* state = new StartThreadState;
state->user_function = function;
state->arg = arg;
PthreadCall("start thread",
pthread_create(&t, nullptr, &StartThreadWrapper, state));
}
} // namespace
static pthread_once_t once = PTHREAD_ONCE_INIT;
static Env* default_env;
static void InitDefaultEnv() { default_env = new PosixEnv; }
void EnvPosixTestHelper::SetReadOnlyFDLimit(int limit) {
assert(default_env == nullptr);
open_read_only_file_limit = limit;
}
void EnvPosixTestHelper::SetReadOnlyMMapLimit(int limit) {
assert(default_env == nullptr);
mmap_limit = limit;
}
Env* Env::Default() {
pthread_once(&once, InitDefaultEnv);
return default_env;
}
} // namespace leveldb