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The QtLockedFile class extends QFile with advisory locking functions. More...
Inherits QFile.
Public Types |
Public Member Functions | |
| QtLockedFile () | |
| QtLockedFile (const QString &name) | |
| ~QtLockedFile () | |
| bool | open (OpenMode mode) |
| bool | lock (LockMode mode, bool block=true) |
| bool | unlock () |
| bool | isLocked () const |
| LockMode | lockMode () const |
The QtLockedFile class extends QFile with advisory locking functions.
A file may be locked in read or write mode. Multiple instances of QtLockedFile, created in multiple processes running on the same machine, may have a file locked in read mode. Exactly one instance may have it locked in write mode. A read and a write lock cannot exist simultaneously on the same file.
The file locks are advisory. This means that nothing prevents another process from manipulating a locked file using QFile or file system functions offered by the OS. Serialization is only guaranteed if all processes that access the file use QLockedFile. Also, while holding a lock on a file, a process must not open the same file again (through any API), or locks can be unexpectedly lost.
The lock provided by an instance of QtLockedFile is released whenever the program terminates. This is true even when the program crashes and no destructors are called.
Definition at line 67 of file qtlockedfile.h.
This enum describes the available lock modes.
ReadLock A read lock. WriteLock A write lock. NoLock Neither a read lock nor a write lock.
Definition at line 70 of file qtlockedfile.h.
| QtLockedFile::QtLockedFile | ( | ) |
Constructs an unlocked QtLockedFile object. This constructor behaves in the same way as QFile::QFile().
Definition at line 83 of file qtlocalpeer.cpp.
| QtLockedFile::QtLockedFile | ( | const QString & | name | ) |
Constructs an unlocked QtLockedFile object with file name. This constructor behaves in the same way as QFile::QFile(const QString&).
Definition at line 100 of file qtlocalpeer.cpp.
| QtLockedFile::~QtLockedFile | ( | ) |
Destroys the QtLockedFile object. If any locks were held, they are released.
Definition at line 110 of file qtlocalpeer.cpp.
| bool QtLockedFile::isLocked | ( | ) | const |
Returns true if this object has a in read or write lock; otherwise returns false.
Definition at line 138 of file qtlocalpeer.cpp.
| bool QtLockedFile::lock | ( | LockMode | mode, |
| bool | block = true |
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| ) |
Obtains a lock of type mode. The file must be opened before it can be locked.
If block is true, this function will block until the lock is aquired. If block is false, this function returns false immediately if the lock cannot be aquired.
If this object already has a lock of type mode, this function returns true immediately. If this object has a lock of a different type than mode, the lock is first released and then a new lock is obtained.
This function returns true if, after it executes, the file is locked by this object, and false otherwise.
Definition at line 48 of file qtlocalpeer.cpp.
| QtLockedFile::LockMode QtLockedFile::lockMode | ( | ) | const |
Returns the type of lock currently held by this object, or QtLockedFile::NoLock.
Definition at line 149 of file qtlocalpeer.cpp.
| bool QtLockedFile::open | ( | OpenMode | mode | ) |
Opens the file in OpenMode mode.
This is identical to QFile::open(), with the one exception that the Truncate mode flag is disallowed. Truncation would conflict with the advisory file locking, since the file would be modified before the write lock is obtained. If truncation is required, use resize(0) after obtaining the write lock.
Returns true if successful; otherwise false.
Definition at line 123 of file qtlocalpeer.cpp.
| bool QtLockedFile::unlock | ( | ) |
Releases a lock.
If the object has no lock, this function returns immediately.
This function returns true if, after it executes, the file is not locked by this object, and false otherwise.
Definition at line 84 of file qtlocalpeer.cpp.
1.8.11
