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893 lines
26 KiB
893 lines
26 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include <dirent.h>
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#include <fcntl.h>
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#include <pthread.h>
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#include <sys/mman.h>
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#include <sys/resource.h>
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#include <sys/stat.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <atomic>
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#include <cerrno>
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#include <cstddef>
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#include <cstdint>
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#include <cstdio>
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#include <cstdlib>
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#include <cstring>
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#include <limits>
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#include <queue>
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#include <set>
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#include <string>
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#include <thread>
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#include <type_traits>
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#include <utility>
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#include "leveldb/env.h"
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#include "leveldb/slice.h"
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#include "leveldb/status.h"
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#include "port/port.h"
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#include "port/thread_annotations.h"
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#include "util/env_posix_test_helper.h"
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#include "util/posix_logger.h"
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namespace leveldb {
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namespace {
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// Set by EnvPosixTestHelper::SetReadOnlyMMapLimit() and MaxOpenFiles().
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int g_open_read_only_file_limit = -1;
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// Up to 1000 mmap regions for 64-bit binaries; none for 32-bit.
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constexpr const int kDefaultMmapLimit = (sizeof(void*) >= 8) ? 1000 : 0;
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// Can be set using EnvPosixTestHelper::SetReadOnlyMMapLimit().
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int g_mmap_limit = kDefaultMmapLimit;
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// Common flags defined for all posix open operations
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#if defined(HAVE_O_CLOEXEC)
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constexpr const int kOpenBaseFlags = O_CLOEXEC;
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#else
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constexpr const int kOpenBaseFlags = 0;
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#endif // defined(HAVE_O_CLOEXEC)
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constexpr const size_t kWritableFileBufferSize = 65536;
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Status PosixError(const std::string& context, int error_number) {
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if (error_number == ENOENT) {
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return Status::NotFound(context, std::strerror(error_number));
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} else {
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return Status::IOError(context, std::strerror(error_number));
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}
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}
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// Helper class to limit resource usage to avoid exhaustion.
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// Currently used to limit read-only file descriptors and mmap file usage
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// so that we do not run out of file descriptors or virtual memory, or run into
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// kernel performance problems for very large databases.
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class Limiter {
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public:
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// Limit maximum number of resources to |max_acquires|.
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Limiter(int max_acquires) : acquires_allowed_(max_acquires) {}
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Limiter(const Limiter&) = delete;
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Limiter operator=(const Limiter&) = delete;
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// If another resource is available, acquire it and return true.
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// Else return false.
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bool Acquire() {
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int old_acquires_allowed =
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acquires_allowed_.fetch_sub(1, std::memory_order_relaxed);
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if (old_acquires_allowed > 0) return true;
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acquires_allowed_.fetch_add(1, std::memory_order_relaxed);
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return false;
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}
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// Release a resource acquired by a previous call to Acquire() that returned
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// true.
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void Release() { acquires_allowed_.fetch_add(1, std::memory_order_relaxed); }
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private:
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// The number of available resources.
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//
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// This is a counter and is not tied to the invariants of any other class, so
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// it can be operated on safely using std::memory_order_relaxed.
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std::atomic<int> acquires_allowed_;
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};
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// Implements sequential read access in a file using read().
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//
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// Instances of this class are thread-friendly but not thread-safe, as required
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// by the SequentialFile API.
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class PosixSequentialFile final : public SequentialFile {
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public:
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PosixSequentialFile(std::string filename, int fd)
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: fd_(fd), filename_(filename) {}
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~PosixSequentialFile() override { close(fd_); }
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Status Read(size_t n, Slice* result, char* scratch) override {
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Status status;
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while (true) {
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::ssize_t read_size = ::read(fd_, scratch, n);
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if (read_size < 0) { // Read error.
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if (errno == EINTR) {
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continue; // Retry
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}
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status = PosixError(filename_, errno);
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break;
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}
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*result = Slice(scratch, read_size);
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break;
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}
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return status;
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}
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Status Skip(uint64_t n) override {
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if (::lseek(fd_, n, SEEK_CUR) == static_cast<off_t>(-1)) {
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return PosixError(filename_, errno);
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}
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return Status::OK();
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}
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private:
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const int fd_;
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const std::string filename_;
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};
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// Implements random read access in a file using pread().
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//
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// Instances of this class are thread-safe, as required by the RandomAccessFile
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// API. Instances are immutable and Read() only calls thread-safe library
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// functions.
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class PosixRandomAccessFile final : public RandomAccessFile {
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public:
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// The new instance takes ownership of |fd|. |fd_limiter| must outlive this
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// instance, and will be used to determine if .
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PosixRandomAccessFile(std::string filename, int fd, Limiter* fd_limiter)
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: has_permanent_fd_(fd_limiter->Acquire()),
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fd_(has_permanent_fd_ ? fd : -1),
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fd_limiter_(fd_limiter),
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filename_(std::move(filename)) {
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if (!has_permanent_fd_) {
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assert(fd_ == -1);
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::close(fd); // The file will be opened on every read.
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}
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}
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~PosixRandomAccessFile() override {
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if (has_permanent_fd_) {
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assert(fd_ != -1);
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::close(fd_);
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fd_limiter_->Release();
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}
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}
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Status Read(uint64_t offset, size_t n, Slice* result,
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char* scratch) const override {
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int fd = fd_;
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if (!has_permanent_fd_) {
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fd = ::open(filename_.c_str(), O_RDONLY | kOpenBaseFlags);
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if (fd < 0) {
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return PosixError(filename_, errno);
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}
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}
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assert(fd != -1);
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Status status;
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ssize_t read_size = ::pread(fd, scratch, n, static_cast<off_t>(offset));
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*result = Slice(scratch, (read_size < 0) ? 0 : read_size);
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if (read_size < 0) {
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// An error: return a non-ok status.
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status = PosixError(filename_, errno);
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}
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if (!has_permanent_fd_) {
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// Close the temporary file descriptor opened earlier.
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assert(fd != fd_);
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::close(fd);
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}
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return status;
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}
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private:
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const bool has_permanent_fd_; // If false, the file is opened on every read.
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const int fd_; // -1 if has_permanent_fd_ is false.
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Limiter* const fd_limiter_;
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const std::string filename_;
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};
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// Implements random read access in a file using mmap().
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//
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// Instances of this class are thread-safe, as required by the RandomAccessFile
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// API. Instances are immutable and Read() only calls thread-safe library
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// functions.
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class PosixMmapReadableFile final : public RandomAccessFile {
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public:
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// mmap_base[0, length-1] points to the memory-mapped contents of the file. It
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// must be the result of a successful call to mmap(). This instances takes
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// over the ownership of the region.
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//
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// |mmap_limiter| must outlive this instance. The caller must have already
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// aquired the right to use one mmap region, which will be released when this
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// instance is destroyed.
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PosixMmapReadableFile(std::string filename, char* mmap_base, size_t length,
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Limiter* mmap_limiter)
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: mmap_base_(mmap_base),
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length_(length),
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mmap_limiter_(mmap_limiter),
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filename_(std::move(filename)) {}
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~PosixMmapReadableFile() override {
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::munmap(static_cast<void*>(mmap_base_), length_);
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mmap_limiter_->Release();
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}
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Status Read(uint64_t offset, size_t n, Slice* result,
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char* scratch) const override {
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if (offset + n > length_) {
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*result = Slice();
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return PosixError(filename_, EINVAL);
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}
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*result = Slice(mmap_base_ + offset, n);
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return Status::OK();
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}
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private:
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char* const mmap_base_;
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const size_t length_;
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Limiter* const mmap_limiter_;
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const std::string filename_;
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};
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class PosixWritableFile final : public WritableFile {
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public:
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PosixWritableFile(std::string filename, int fd)
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: pos_(0),
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fd_(fd),
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is_manifest_(IsManifest(filename)),
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filename_(std::move(filename)),
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dirname_(Dirname(filename_)) {}
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~PosixWritableFile() override {
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if (fd_ >= 0) {
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// Ignoring any potential errors
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Close();
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}
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}
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Status Append(const Slice& data) override {
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size_t write_size = data.size();
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const char* write_data = data.data();
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// Fit as much as possible into buffer.
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size_t copy_size = std::min(write_size, kWritableFileBufferSize - pos_);
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std::memcpy(buf_ + pos_, write_data, copy_size);
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write_data += copy_size;
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write_size -= copy_size;
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pos_ += copy_size;
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if (write_size == 0) {
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return Status::OK();
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}
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// Can't fit in buffer, so need to do at least one write.
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Status status = FlushBuffer();
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if (!status.ok()) {
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return status;
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}
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// Small writes go to buffer, large writes are written directly.
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if (write_size < kWritableFileBufferSize) {
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std::memcpy(buf_, write_data, write_size);
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pos_ = write_size;
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return Status::OK();
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}
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return WriteUnbuffered(write_data, write_size);
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}
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Status Close() override {
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Status status = FlushBuffer();
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const int close_result = ::close(fd_);
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if (close_result < 0 && status.ok()) {
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status = PosixError(filename_, errno);
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}
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fd_ = -1;
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return status;
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}
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Status Flush() override { return FlushBuffer(); }
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Status Sync() override {
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// Ensure new files referred to by the manifest are in the filesystem.
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//
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// This needs to happen before the manifest file is flushed to disk, to
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// avoid crashing in a state where the manifest refers to files that are not
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// yet on disk.
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Status status = SyncDirIfManifest();
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if (!status.ok()) {
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return status;
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}
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status = FlushBuffer();
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if (!status.ok()) {
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return status;
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}
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return SyncFd(fd_, filename_);
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}
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private:
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Status FlushBuffer() {
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Status status = WriteUnbuffered(buf_, pos_);
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pos_ = 0;
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return status;
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}
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Status WriteUnbuffered(const char* data, size_t size) {
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while (size > 0) {
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ssize_t write_result = ::write(fd_, data, size);
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if (write_result < 0) {
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if (errno == EINTR) {
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continue; // Retry
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}
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return PosixError(filename_, errno);
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}
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data += write_result;
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size -= write_result;
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}
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return Status::OK();
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}
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Status SyncDirIfManifest() {
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Status status;
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if (!is_manifest_) {
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return status;
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}
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int fd = ::open(dirname_.c_str(), O_RDONLY | kOpenBaseFlags);
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if (fd < 0) {
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status = PosixError(dirname_, errno);
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} else {
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status = SyncFd(fd, dirname_);
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::close(fd);
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}
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return status;
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}
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// Ensures that all the caches associated with the given file descriptor's
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// data are flushed all the way to durable media, and can withstand power
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// failures.
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//
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// The path argument is only used to populate the description string in the
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// returned Status if an error occurs.
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static Status SyncFd(int fd, const std::string& fd_path) {
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#if HAVE_FULLFSYNC
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// On macOS and iOS, fsync() doesn't guarantee durability past power
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// failures. fcntl(F_FULLFSYNC) is required for that purpose. Some
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// filesystems don't support fcntl(F_FULLFSYNC), and require a fallback to
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// fsync().
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if (::fcntl(fd, F_FULLFSYNC) == 0) {
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return Status::OK();
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}
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#endif // HAVE_FULLFSYNC
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#if HAVE_FDATASYNC
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bool sync_success = ::fdatasync(fd) == 0;
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#else
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bool sync_success = ::fsync(fd) == 0;
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#endif // HAVE_FDATASYNC
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if (sync_success) {
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return Status::OK();
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}
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return PosixError(fd_path, errno);
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}
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// Returns the directory name in a path pointing to a file.
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//
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// Returns "." if the path does not contain any directory separator.
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static std::string Dirname(const std::string& filename) {
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std::string::size_type separator_pos = filename.rfind('/');
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if (separator_pos == std::string::npos) {
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return std::string(".");
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}
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// The filename component should not contain a path separator. If it does,
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// the splitting was done incorrectly.
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assert(filename.find('/', separator_pos + 1) == std::string::npos);
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return filename.substr(0, separator_pos);
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}
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// Extracts the file name from a path pointing to a file.
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//
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// The returned Slice points to |filename|'s data buffer, so it is only valid
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// while |filename| is alive and unchanged.
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static Slice Basename(const std::string& filename) {
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std::string::size_type separator_pos = filename.rfind('/');
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if (separator_pos == std::string::npos) {
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return Slice(filename);
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}
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// The filename component should not contain a path separator. If it does,
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// the splitting was done incorrectly.
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assert(filename.find('/', separator_pos + 1) == std::string::npos);
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return Slice(filename.data() + separator_pos + 1,
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filename.length() - separator_pos - 1);
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}
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// True if the given file is a manifest file.
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static bool IsManifest(const std::string& filename) {
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return Basename(filename).starts_with("MANIFEST");
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}
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// buf_[0, pos_ - 1] contains data to be written to fd_.
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char buf_[kWritableFileBufferSize];
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size_t pos_;
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int fd_;
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const bool is_manifest_; // True if the file's name starts with MANIFEST.
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const std::string filename_;
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const std::string dirname_; // The directory of filename_.
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};
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int LockOrUnlock(int fd, bool lock) {
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errno = 0;
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struct ::flock file_lock_info;
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std::memset(&file_lock_info, 0, sizeof(file_lock_info));
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file_lock_info.l_type = (lock ? F_WRLCK : F_UNLCK);
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file_lock_info.l_whence = SEEK_SET;
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file_lock_info.l_start = 0;
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file_lock_info.l_len = 0; // Lock/unlock entire file.
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return ::fcntl(fd, F_SETLK, &file_lock_info);
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}
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// Instances are thread-safe because they are immutable.
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class PosixFileLock : public FileLock {
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public:
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PosixFileLock(int fd, std::string filename)
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: fd_(fd), filename_(std::move(filename)) {}
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int fd() const { return fd_; }
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const std::string& filename() const { return filename_; }
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private:
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const int fd_;
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const std::string filename_;
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};
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// Tracks the files locked by PosixEnv::LockFile().
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//
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// We maintain a separate set instead of relying on fcntl(F_SETLK) because
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// fcntl(F_SETLK) does not provide any protection against multiple uses from the
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// same process.
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//
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// Instances are thread-safe because all member data is guarded by a mutex.
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class PosixLockTable {
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public:
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bool Insert(const std::string& fname) LOCKS_EXCLUDED(mu_) {
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mu_.Lock();
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bool succeeded = locked_files_.insert(fname).second;
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mu_.Unlock();
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return succeeded;
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}
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void Remove(const std::string& fname) LOCKS_EXCLUDED(mu_) {
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mu_.Lock();
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locked_files_.erase(fname);
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mu_.Unlock();
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}
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private:
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port::Mutex mu_;
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std::set<std::string> locked_files_ GUARDED_BY(mu_);
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};
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class PosixEnv : public Env {
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public:
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PosixEnv();
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~PosixEnv() override {
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static const char msg[] =
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"PosixEnv singleton destroyed. Unsupported behavior!\n";
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std::fwrite(msg, 1, sizeof(msg), stderr);
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std::abort();
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}
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Status NewSequentialFile(const std::string& filename,
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SequentialFile** result) override {
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int fd = ::open(filename.c_str(), O_RDONLY | kOpenBaseFlags);
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if (fd < 0) {
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*result = nullptr;
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return PosixError(filename, errno);
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}
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*result = new PosixSequentialFile(filename, fd);
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return Status::OK();
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}
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Status NewRandomAccessFile(const std::string& filename,
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RandomAccessFile** result) override {
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*result = nullptr;
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int fd = ::open(filename.c_str(), O_RDONLY | kOpenBaseFlags);
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if (fd < 0) {
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return PosixError(filename, errno);
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}
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if (!mmap_limiter_.Acquire()) {
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*result = new PosixRandomAccessFile(filename, fd, &fd_limiter_);
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return Status::OK();
|
|
}
|
|
|
|
uint64_t file_size;
|
|
Status status = GetFileSize(filename, &file_size);
|
|
if (status.ok()) {
|
|
void* mmap_base =
|
|
::mmap(/*addr=*/nullptr, file_size, PROT_READ, MAP_SHARED, fd, 0);
|
|
if (mmap_base != MAP_FAILED) {
|
|
*result = new PosixMmapReadableFile(filename,
|
|
reinterpret_cast<char*>(mmap_base),
|
|
file_size, &mmap_limiter_);
|
|
} else {
|
|
status = PosixError(filename, errno);
|
|
}
|
|
}
|
|
::close(fd);
|
|
if (!status.ok()) {
|
|
mmap_limiter_.Release();
|
|
}
|
|
return status;
|
|
}
|
|
|
|
Status NewWritableFile(const std::string& filename,
|
|
WritableFile** result) override {
|
|
int fd = ::open(filename.c_str(),
|
|
O_TRUNC | O_WRONLY | O_CREAT | kOpenBaseFlags, 0644);
|
|
if (fd < 0) {
|
|
*result = nullptr;
|
|
return PosixError(filename, errno);
|
|
}
|
|
|
|
*result = new PosixWritableFile(filename, fd);
|
|
return Status::OK();
|
|
}
|
|
|
|
Status NewAppendableFile(const std::string& filename,
|
|
WritableFile** result) override {
|
|
int fd = ::open(filename.c_str(),
|
|
O_APPEND | O_WRONLY | O_CREAT | kOpenBaseFlags, 0644);
|
|
if (fd < 0) {
|
|
*result = nullptr;
|
|
return PosixError(filename, errno);
|
|
}
|
|
|
|
*result = new PosixWritableFile(filename, fd);
|
|
return Status::OK();
|
|
}
|
|
|
|
bool FileExists(const std::string& filename) override {
|
|
return ::access(filename.c_str(), F_OK) == 0;
|
|
}
|
|
|
|
Status GetChildren(const std::string& directory_path,
|
|
std::vector<std::string>* result) override {
|
|
result->clear();
|
|
::DIR* dir = ::opendir(directory_path.c_str());
|
|
if (dir == nullptr) {
|
|
return PosixError(directory_path, errno);
|
|
}
|
|
struct ::dirent* entry;
|
|
while ((entry = ::readdir(dir)) != nullptr) {
|
|
result->emplace_back(entry->d_name);
|
|
}
|
|
::closedir(dir);
|
|
return Status::OK();
|
|
}
|
|
|
|
Status RemoveFile(const std::string& filename) override {
|
|
if (::unlink(filename.c_str()) != 0) {
|
|
return PosixError(filename, errno);
|
|
}
|
|
return Status::OK();
|
|
}
|
|
|
|
Status CreateDir(const std::string& dirname) override {
|
|
if (::mkdir(dirname.c_str(), 0755) != 0) {
|
|
return PosixError(dirname, errno);
|
|
}
|
|
return Status::OK();
|
|
}
|
|
|
|
Status RemoveDir(const std::string& dirname) override {
|
|
if (::rmdir(dirname.c_str()) != 0) {
|
|
return PosixError(dirname, errno);
|
|
}
|
|
return Status::OK();
|
|
}
|
|
|
|
Status GetFileSize(const std::string& filename, uint64_t* size) override {
|
|
struct ::stat file_stat;
|
|
if (::stat(filename.c_str(), &file_stat) != 0) {
|
|
*size = 0;
|
|
return PosixError(filename, errno);
|
|
}
|
|
*size = file_stat.st_size;
|
|
return Status::OK();
|
|
}
|
|
|
|
Status RenameFile(const std::string& from, const std::string& to) override {
|
|
if (std::rename(from.c_str(), to.c_str()) != 0) {
|
|
return PosixError(from, errno);
|
|
}
|
|
return Status::OK();
|
|
}
|
|
|
|
Status LockFile(const std::string& filename, FileLock** lock) override {
|
|
*lock = nullptr;
|
|
|
|
int fd = ::open(filename.c_str(), O_RDWR | O_CREAT | kOpenBaseFlags, 0644);
|
|
if (fd < 0) {
|
|
return PosixError(filename, errno);
|
|
}
|
|
|
|
if (!locks_.Insert(filename)) {
|
|
::close(fd);
|
|
return Status::IOError("lock " + filename, "already held by process");
|
|
}
|
|
|
|
if (LockOrUnlock(fd, true) == -1) {
|
|
int lock_errno = errno;
|
|
::close(fd);
|
|
locks_.Remove(filename);
|
|
return PosixError("lock " + filename, lock_errno);
|
|
}
|
|
|
|
*lock = new PosixFileLock(fd, filename);
|
|
return Status::OK();
|
|
}
|
|
|
|
Status UnlockFile(FileLock* lock) override {
|
|
PosixFileLock* posix_file_lock = static_cast<PosixFileLock*>(lock);
|
|
if (LockOrUnlock(posix_file_lock->fd(), false) == -1) {
|
|
return PosixError("unlock " + posix_file_lock->filename(), errno);
|
|
}
|
|
locks_.Remove(posix_file_lock->filename());
|
|
::close(posix_file_lock->fd());
|
|
delete posix_file_lock;
|
|
return Status::OK();
|
|
}
|
|
|
|
void Schedule(void (*background_work_function)(void* background_work_arg),
|
|
void* background_work_arg) override;
|
|
|
|
void StartThread(void (*thread_main)(void* thread_main_arg),
|
|
void* thread_main_arg) override {
|
|
std::thread new_thread(thread_main, thread_main_arg);
|
|
new_thread.detach();
|
|
}
|
|
|
|
Status GetTestDirectory(std::string* result) override {
|
|
const char* env = std::getenv("TEST_TMPDIR");
|
|
if (env && env[0] != '\0') {
|
|
*result = env;
|
|
} else {
|
|
char buf[100];
|
|
std::snprintf(buf, sizeof(buf), "/tmp/leveldbtest-%d",
|
|
static_cast<int>(::geteuid()));
|
|
*result = buf;
|
|
}
|
|
|
|
// The CreateDir status is ignored because the directory may already exist.
|
|
CreateDir(*result);
|
|
|
|
return Status::OK();
|
|
}
|
|
|
|
Status NewLogger(const std::string& filename, Logger** result) override {
|
|
int fd = ::open(filename.c_str(),
|
|
O_APPEND | O_WRONLY | O_CREAT | kOpenBaseFlags, 0644);
|
|
if (fd < 0) {
|
|
*result = nullptr;
|
|
return PosixError(filename, errno);
|
|
}
|
|
|
|
std::FILE* fp = ::fdopen(fd, "w");
|
|
if (fp == nullptr) {
|
|
::close(fd);
|
|
*result = nullptr;
|
|
return PosixError(filename, errno);
|
|
} else {
|
|
*result = new PosixLogger(fp);
|
|
return Status::OK();
|
|
}
|
|
}
|
|
|
|
uint64_t NowMicros() override {
|
|
static constexpr uint64_t kUsecondsPerSecond = 1000000;
|
|
struct ::timeval tv;
|
|
::gettimeofday(&tv, nullptr);
|
|
return static_cast<uint64_t>(tv.tv_sec) * kUsecondsPerSecond + tv.tv_usec;
|
|
}
|
|
|
|
void SleepForMicroseconds(int micros) override {
|
|
std::this_thread::sleep_for(std::chrono::microseconds(micros));
|
|
}
|
|
|
|
private:
|
|
void BackgroundThreadMain();
|
|
|
|
static void BackgroundThreadEntryPoint(PosixEnv* env) {
|
|
env->BackgroundThreadMain();
|
|
}
|
|
|
|
// Stores the work item data in a Schedule() call.
|
|
//
|
|
// Instances are constructed on the thread calling Schedule() and used on the
|
|
// background thread.
|
|
//
|
|
// This structure is thread-safe beacuse it is immutable.
|
|
struct BackgroundWorkItem {
|
|
explicit BackgroundWorkItem(void (*function)(void* arg), void* arg)
|
|
: function(function), arg(arg) {}
|
|
|
|
void (*const function)(void*);
|
|
void* const arg;
|
|
};
|
|
|
|
port::Mutex background_work_mutex_;
|
|
port::CondVar background_work_cv_ GUARDED_BY(background_work_mutex_);
|
|
bool started_background_thread_ GUARDED_BY(background_work_mutex_);
|
|
|
|
std::queue<BackgroundWorkItem> background_work_queue_
|
|
GUARDED_BY(background_work_mutex_);
|
|
|
|
PosixLockTable locks_; // Thread-safe.
|
|
Limiter mmap_limiter_; // Thread-safe.
|
|
Limiter fd_limiter_; // Thread-safe.
|
|
};
|
|
|
|
// Return the maximum number of concurrent mmaps.
|
|
int MaxMmaps() { return g_mmap_limit; }
|
|
|
|
// Return the maximum number of read-only files to keep open.
|
|
int MaxOpenFiles() {
|
|
if (g_open_read_only_file_limit >= 0) {
|
|
return g_open_read_only_file_limit;
|
|
}
|
|
struct ::rlimit rlim;
|
|
if (::getrlimit(RLIMIT_NOFILE, &rlim)) {
|
|
// getrlimit failed, fallback to hard-coded default.
|
|
g_open_read_only_file_limit = 50;
|
|
} else if (rlim.rlim_cur == RLIM_INFINITY) {
|
|
g_open_read_only_file_limit = std::numeric_limits<int>::max();
|
|
} else {
|
|
// Allow use of 20% of available file descriptors for read-only files.
|
|
g_open_read_only_file_limit = rlim.rlim_cur / 5;
|
|
}
|
|
return g_open_read_only_file_limit;
|
|
}
|
|
|
|
} // namespace
|
|
|
|
PosixEnv::PosixEnv()
|
|
: background_work_cv_(&background_work_mutex_),
|
|
started_background_thread_(false),
|
|
mmap_limiter_(MaxMmaps()),
|
|
fd_limiter_(MaxOpenFiles()) {}
|
|
|
|
void PosixEnv::Schedule(
|
|
void (*background_work_function)(void* background_work_arg),
|
|
void* background_work_arg) {
|
|
background_work_mutex_.Lock();
|
|
|
|
// Start the background thread, if we haven't done so already.
|
|
if (!started_background_thread_) {
|
|
started_background_thread_ = true;
|
|
std::thread background_thread(PosixEnv::BackgroundThreadEntryPoint, this);
|
|
background_thread.detach();
|
|
}
|
|
|
|
// If the queue is empty, the background thread may be waiting for work.
|
|
if (background_work_queue_.empty()) {
|
|
background_work_cv_.Signal();
|
|
}
|
|
|
|
background_work_queue_.emplace(background_work_function, background_work_arg);
|
|
background_work_mutex_.Unlock();
|
|
}
|
|
|
|
void PosixEnv::BackgroundThreadMain() {
|
|
while (true) {
|
|
background_work_mutex_.Lock();
|
|
|
|
// Wait until there is work to be done.
|
|
while (background_work_queue_.empty()) {
|
|
background_work_cv_.Wait();
|
|
}
|
|
|
|
assert(!background_work_queue_.empty());
|
|
auto background_work_function = background_work_queue_.front().function;
|
|
void* background_work_arg = background_work_queue_.front().arg;
|
|
background_work_queue_.pop();
|
|
|
|
background_work_mutex_.Unlock();
|
|
background_work_function(background_work_arg);
|
|
}
|
|
}
|
|
|
|
namespace {
|
|
|
|
// Wraps an Env instance whose destructor is never created.
|
|
//
|
|
// Intended usage:
|
|
// using PlatformSingletonEnv = SingletonEnv<PlatformEnv>;
|
|
// void ConfigurePosixEnv(int param) {
|
|
// PlatformSingletonEnv::AssertEnvNotInitialized();
|
|
// // set global configuration flags.
|
|
// }
|
|
// Env* Env::Default() {
|
|
// static PlatformSingletonEnv default_env;
|
|
// return default_env.env();
|
|
// }
|
|
template <typename EnvType>
|
|
class SingletonEnv {
|
|
public:
|
|
SingletonEnv() {
|
|
#if !defined(NDEBUG)
|
|
env_initialized_.store(true, std::memory_order::memory_order_relaxed);
|
|
#endif // !defined(NDEBUG)
|
|
static_assert(sizeof(env_storage_) >= sizeof(EnvType),
|
|
"env_storage_ will not fit the Env");
|
|
static_assert(alignof(decltype(env_storage_)) >= alignof(EnvType),
|
|
"env_storage_ does not meet the Env's alignment needs");
|
|
new (&env_storage_) EnvType();
|
|
}
|
|
~SingletonEnv() = default;
|
|
|
|
SingletonEnv(const SingletonEnv&) = delete;
|
|
SingletonEnv& operator=(const SingletonEnv&) = delete;
|
|
|
|
Env* env() { return reinterpret_cast<Env*>(&env_storage_); }
|
|
|
|
static void AssertEnvNotInitialized() {
|
|
#if !defined(NDEBUG)
|
|
assert(!env_initialized_.load(std::memory_order::memory_order_relaxed));
|
|
#endif // !defined(NDEBUG)
|
|
}
|
|
|
|
private:
|
|
typename std::aligned_storage<sizeof(EnvType), alignof(EnvType)>::type
|
|
env_storage_;
|
|
#if !defined(NDEBUG)
|
|
static std::atomic<bool> env_initialized_;
|
|
#endif // !defined(NDEBUG)
|
|
};
|
|
|
|
#if !defined(NDEBUG)
|
|
template <typename EnvType>
|
|
std::atomic<bool> SingletonEnv<EnvType>::env_initialized_;
|
|
#endif // !defined(NDEBUG)
|
|
|
|
using PosixDefaultEnv = SingletonEnv<PosixEnv>;
|
|
|
|
} // namespace
|
|
|
|
void EnvPosixTestHelper::SetReadOnlyFDLimit(int limit) {
|
|
PosixDefaultEnv::AssertEnvNotInitialized();
|
|
g_open_read_only_file_limit = limit;
|
|
}
|
|
|
|
void EnvPosixTestHelper::SetReadOnlyMMapLimit(int limit) {
|
|
PosixDefaultEnv::AssertEnvNotInitialized();
|
|
g_mmap_limit = limit;
|
|
}
|
|
|
|
Env* Env::Default() {
|
|
static PosixDefaultEnv env_container;
|
|
return env_container.env();
|
|
}
|
|
|
|
} // namespace leveldb
|