File system programming guide mac os x

Every file or file package located in the Documents subdirectory or one of its subdirectories is presented to the user via the iCloud UI in macOS and iOS as a separate document that can be deleted individually. Anything not in Documents or one of its subdirectories is treated as data and shown as a single entry in the iCloud UI. Documents that the user creates and sees in an app's user interface—for example the document browsers in Pages, Numbers, and Keynote should be stored in the Documents directory.

Another example of files that might go in the Documents directory are saved games, again because they are something that an app could potentially provide some sort of method for selecting. Anything that the app does not want the user to see or modify directly should be placed outside of the Documents directory. Apps can create any subdirectories inside the container directory, so they can arrange private files as desired. Apps create files and directories in iCloud container directories in exactly the same way as they create local files and directories.

They are also more flexible than most other techniques because you can use them to represent any type of data, not just files and directories. Examples of UTIs include:. Whenever a UTI-based interface is available for specifying file types, you should prefer that interface over any others. Many macOS interfaces allow you to specify UTIs corresponding to the files or directories you want to work with. For example, in the Open panel, you can use UTIs as file filters and limit the types of files the user selects to ones your app can handle.

One way the system determines the UTI for a given file is by looking at its filename extension. A filename extension is a string of characters appended to the end of a file and separated from the main filename with a period.

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Each unique string of characters identifies a file of a specific type. For example, the. The CFBundleDocumentTypes key specifies the file formats that your app recognizes and is able to open. Entries for any custom file formats should include both a filename extension and UTI corresponding to the file contents. The system uses that information to direct files with the appropriate type to your app. Because all user data and system code are stored on disk somewhere, protecting the integrity of files and the file system is an important job. For that reason, there are several ways to secure content and prevent it from being stolen or damaged by other processes.

For general information about secure coding practices when working with files, see Secure Coding Guide. In iOS and in macOS Each sandboxed app receives one or more containers that it can write into. Developers writing apps for macOS Developers of iOS apps do not have to explicitly put their app in a sandbox because the system does it for them automatically at install time. For more information about sandboxes and the types of restrictions they impose on file system access, see Mac App Programming Guide and App Sandbox Design Guide.

Access control lists are a set of fine-grained controls that define exactly what can and cannot be done to a file or directory and by whom.

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With access control lists, you can grant individual users different levels of access to a given file or directory. See Security Overview for more information. Because iOS apps always run in a sandbox, the system assigns specific ACLs and permissions to files created by each app. However, macOS apps can use Identity Services to manage access control lists for files to which they have access.

An iOS app can designate files that it wants to be encrypted on disk. When the user unlocks a device containing encrypted files, the system creates a decryption key that allows the app to access its encrypted files. When the user locks the device, though, the decryption key is destroyed to prevent unauthorized access to the files.

Users can encrypt the contents of a volume using the Disk Utility app. The contents of an encrypted disk are available to apps only while the computer is running. In iOS, apps that take advantage of disk-based encryption need to be discontinue the use of encrypted files when the user locks the device.

Because locking the device destroys the decryption keys, access to encrypted files is limited to when the device is unlocked. If your iOS app can run in the background while the device is locked, it must do so without access to any of its encrypted files. Because encrypted disks in macOS are always accessible while the computer is running, macOS apps do not need to do anything special to handle disk-level encryption. The file system is a resource shared by third-party apps and system apps. If the second app is not prepared to handle such changes, it could enter an unknown state or even crash.

In cases where your app relies on the presence of specific files, you can use synchronization interfaces to be notified of changes to those files. File system synchronization is primarily an issue in macOS, where the user can manipulate files directly with the Finder or with any number of other apps at the same time. Fortunately, macOS provides the following interfaces to help with synchronization issues:.

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File coordinators. Because file-related operations involve interacting with the hard disk and are therefore slow compared to most other operations, most of the file-related interfaces in iOS and macOS are designed with concurrency in mind. Several technologies incorporate asynchronous operation into their design and most others can execute safely from a dispatch queue or secondary thread.

Table lists some of the key technologies discussed in this document and whether they are safe to use from specific threads or any thread.

For specific information about the capabilities of any interface, see the reference documentation for that interface. For most tasks, it is safe to use the default NSFileManager object simultaneously from multiple background threads. When using a file manager object with a delegate, it is recommended that you create a unique instance of the NSFileManager class and use your delegate with that instance.

You should then use your unique instance from one thread at a time. GCD itself is safe to use from any thread. However, you are still responsible for writing your blocks in a way that is thread safe. Most of the Foundation objects you use to read and write file data can be used from any single thread but should not be used from multiple threads simultaneously.


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For details, see the corresponding man pages. The immutable objects you use to specify paths are safe to use from any thread. Because they are immutable, you can also refer to them from multiple threads simultaneously. Of course, the mutable versions of these objects should be used from only one thread at a time. NSEnumerator and its subclasses. Enumerator objects are safe to use from any single thread but should not be used from multiple threads simultaneously.

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Even if you use an thread-safe interface for manipulating a file, problems can still arise when multiple threads or multiple processes attempt to act on the same file. Although there are safeguards to prevent multiple clients from modifying a file at the same time, those safeguards do not always guarantee exclusive access to the file at all times. Nor should you attempt to prevent other processes from accessing shared files.

To make sure your code knows about changes made to shared files, use file coordinators to manage access to those files. All Rights Reserved.

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Next Previous. For more information, see the Resource Programming Guide The contents of this directory are not backed up by iTunes or iCloud. The contents of this directory are backed up by iTunes and iCloud. This directory is part of the local domain. Library There are multiple Library directories on the system, each one associated with a different domain or specific user. This directory comprises the contents of the system domain. Documents —Contains user documents and files. Downloads —Contains files downloaded from the Internet.

Library —Contains user-specific app files hidden in macOS Public —Contains content the user wants to share. In iOS, the contents of this directory are backed up by iTunes and iCloud. Caches Use this directory to write any app-specific support files that your app can re-create easily. Frameworks In macOS, frameworks that must be shared by multiple apps can be installed in either the local or user domain. In iOS, apps cannot install custom frameworks.

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Preferences This directory contains app-specific preference files. NSFileHandle , NSData , Cocoa streams Most of the Foundation objects you use to read and write file data can be used from any single thread but should not be used from multiple threads simultaneously. The command-line tools above refer to versions prior to Cordova 3.

See The Command-Line Interface for information about the current interface. Once Xcode is installed, several command-line tools need to be enabled for Cordova to run. From the Xcode menu, select Preferences , then the Downloads tab. For example, in a source-code directory:. Microsoft Windows may work, but is not a supported platform.