implement chrono conversions for unusual duration types

[folly.git] / folly / File.h

diff --git a/folly/File.h b/folly/File.h
index e990c91bfc14efcd0274dc01c6c84edf63237315..958347d2b40d96e38164ccb7d2e4bafbc8a80121 100644 (file)
--- a/folly/File.h
+++ b/folly/File.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,12 +14,20 @@
  * limitations under the License.
  */
 
-#ifndef FOLLY_FILE_H_
-#define FOLLY_FILE_H_
+#pragma once
 
+#include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <fcntl.h>
+
+#include <string>
+#include <system_error>
+
+#include <folly/ExceptionWrapper.h>
+#include <folly/Expected.h>
+#include <folly/Portability.h>
+#include <folly/Range.h>
+#include <folly/portability/Unistd.h>
 
 namespace folly {
 
@@ -31,21 +39,36 @@ class File {
   /**
    * Creates an empty File object, for late initialization.
    */
-  File();
+  File() noexcept;
 
   /**
    * Create a File object from an existing file descriptor.
    * Takes ownership of the file descriptor if ownsFd is true.
    */
-  /* implicit */ File(int fd,
-                      bool ownsFd = false);
+  explicit File(int fd, bool ownsFd = false) noexcept;
 
   /**
    * Open and create a file object.  Throws on error.
+   * Owns the file descriptor implicitly.
+   */
+  explicit File(const char* name, int flags = O_RDONLY, mode_t mode = 0666);
+  explicit File(
+      const std::string& name, int flags = O_RDONLY, mode_t mode = 0666);
+  explicit File(StringPiece name, int flags = O_RDONLY, mode_t mode = 0666);
+
+  /**
+   * All the constructors that are not noexcept can throw std::system_error.
+   * This is a helper method to use folly::Expected to chain a file open event
+   * to something else you want to do with the open fd.
    */
-  /* implicit */ File(const char* name,
-                      int flags = O_RDONLY,
-                      mode_t mode = 0644);
+  template <typename... Args>
+  static Expected<File, exception_wrapper> makeFile(Args&&... args) noexcept {
+    try {
+      return File(std::forward<Args>(args)...);
+    } catch (const std::system_error& se) {
+      return makeUnexpected(exception_wrapper(std::current_exception(), se));
+    }
+  }
 
   ~File();
 
@@ -63,9 +86,14 @@ class File {
    * Returns 'true' iff the file was successfully opened.
    */
   explicit operator bool() const {
-    return fd_ >= 0;
+    return fd_ != -1;
   }
 
+  /**
+   * Duplicate file descriptor and return File that owns it.
+   */
+  File dup() const;
+
   /**
    * If we own the file descriptor, close the file and throw on error.
    * Otherwise, do nothing.
@@ -79,9 +107,10 @@ class File {
   bool closeNoThrow();
 
   /**
-   * Releases the file descriptor; no longer owned by this File.
+   * Returns and releases the file descriptor; no longer owned by this File.
+   * Returns -1 if the File object didn't wrap a file.
    */
-  void release();
+  int release() noexcept;
 
   /**
    * Swap this File with another.
@@ -89,10 +118,29 @@ class File {
   void swap(File& other);
 
   // movable
-  File(File&&);
+  File(File&&) noexcept;
   File& operator=(File&&);
 
+  // FLOCK (INTERPROCESS) LOCKS
+  //
+  // NOTE THAT THESE LOCKS ARE flock() LOCKS.  That is, they may only be used
+  // for inter-process synchronization -- an attempt to acquire a second lock
+  // on the same file descriptor from the same process may succeed.  Attempting
+  // to acquire a second lock on a different file descriptor for the same file
+  // should fail, but some systems might implement flock() using fcntl() locks,
+  // in which case it will succeed.
+  void lock();
+  bool try_lock();
+  void unlock();
+
+  void lock_shared();
+  bool try_lock_shared();
+  void unlock_shared();
+
  private:
+  void doLock(int op);
+  bool doTryLock(int op);
+
   // unique
   File(const File&) = delete;
   File& operator=(const File&) = delete;
@@ -103,6 +151,4 @@ class File {
 
 void swap(File& a, File& b);
 
-}  // namespace folly
-
-#endif /* FOLLY_FILE_H_ */
+} // namespace folly