159 lines
3.9 KiB
C++
159 lines
3.9 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <fcntl.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <string>
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#include <system_error>
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#include <folly/ExceptionWrapper.h>
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#include <folly/Expected.h>
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#include <folly/Portability.h>
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#include <folly/Range.h>
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#include <folly/portability/Unistd.h>
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namespace folly {
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/**
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* A File represents an open file.
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*/
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class File {
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public:
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/**
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* Creates an empty File object, for late initialization.
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*/
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File() noexcept;
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/**
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* Create a File object from an existing file descriptor.
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* Takes ownership of the file descriptor if ownsFd is true.
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*/
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explicit File(int fd, bool ownsFd = false) noexcept;
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/**
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* Open and create a file object. Throws on error.
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* Owns the file descriptor implicitly.
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*/
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explicit File(const char* name, int flags = O_RDONLY, mode_t mode = 0666);
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explicit File(
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const std::string& name,
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int flags = O_RDONLY,
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mode_t mode = 0666);
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explicit File(StringPiece name, int flags = O_RDONLY, mode_t mode = 0666);
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/**
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* All the constructors that are not noexcept can throw std::system_error.
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* This is a helper method to use folly::Expected to chain a file open event
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* to something else you want to do with the open fd.
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*/
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template <typename... Args>
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static Expected<File, exception_wrapper> makeFile(Args&&... args) noexcept {
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try {
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return File(std::forward<Args>(args)...);
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} catch (const std::system_error& se) {
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return makeUnexpected(exception_wrapper(std::current_exception(), se));
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}
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}
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~File();
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/**
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* Create and return a temporary, owned file (uses tmpfile()).
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*/
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static File temporary();
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/**
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* Return the file descriptor, or -1 if the file was closed.
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*/
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int fd() const {
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return fd_;
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}
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/**
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* Returns 'true' iff the file was successfully opened.
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*/
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explicit operator bool() const {
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return fd_ != -1;
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}
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/**
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* Duplicate file descriptor and return File that owns it.
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*/
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File dup() const;
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/**
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* If we own the file descriptor, close the file and throw on error.
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* Otherwise, do nothing.
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*/
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void close();
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/**
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* Closes the file (if owned). Returns true on success, false (and sets
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* errno) on error.
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*/
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bool closeNoThrow();
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/**
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* Returns and releases the file descriptor; no longer owned by this File.
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* Returns -1 if the File object didn't wrap a file.
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*/
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int release() noexcept;
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/**
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* Swap this File with another.
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*/
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void swap(File& other) noexcept;
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// movable
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File(File&&) noexcept;
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File& operator=(File&&);
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// FLOCK (INTERPROCESS) LOCKS
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//
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// NOTE THAT THESE LOCKS ARE flock() LOCKS. That is, they may only be used
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// for inter-process synchronization -- an attempt to acquire a second lock
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// on the same file descriptor from the same process may succeed. Attempting
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// to acquire a second lock on a different file descriptor for the same file
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// should fail, but some systems might implement flock() using fcntl() locks,
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// in which case it will succeed.
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void lock();
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bool try_lock();
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void unlock();
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void lock_shared();
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bool try_lock_shared();
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void unlock_shared();
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private:
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void doLock(int op);
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bool doTryLock(int op);
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// unique
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File(const File&) = delete;
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File& operator=(const File&) = delete;
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int fd_;
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bool ownsFd_;
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};
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void swap(File& a, File& b) noexcept;
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} // namespace folly
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