Qore Programming Language Reference Manual 0.8.8

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Qore::Thread::AutoReadLock Class Reference

A helper class for the RWLock class for exception-safe read lock handling. More...

## Public Member Functions
| constructor (RWLock rwl)
| Creates the AutoReadLock object based on the RWLock argument passed and immediately calls RWLock::readLock() More...
| copy ()
| Throws an exception; objects of this class cannot be copied. More...
| destructor ()
| Calls RWLock::readUnlock() on the saved RWLock and destroys the AutoReadLock object. More...

## Detailed Description

A helper class for the RWLock class for exception-safe read lock handling.

Restrictions:
  Qore::PO_NO_THREAD_CLASSES

AutoReadLock objects, when used along with a RWLock object, allow Qore programmers to safely acquire and release a read lock, even if exceptions are thrown or return statements are executed in the block where the AutoReadLock object is created.

AutoReadLock objects are helper objects that acquire a read lock for the lifetime of the AutoReadLock object. For this reason, it is only appropriate to assign an AutoReadLock object to a local variable, so when the local variable goes out of scope, the AutoReadLock object will be deleted and the read lock will be automatically released.

For example:

our RWLock $rwl();
sub check_error($error) {
# note that the read lock is acquired in the AutoReadLock constructor, and
# the read lock will be released as soon as the block is exited below.
# (with either the throw statement or the return statement)
my AutoReadLock $arl($rwl);
if ($error)
throw "ERROR", "sorry, an error happened";
return "OK";
}

Note
  This class is not available with the PO_NO_THREAD_CLASSES parse option

## Member Function Documentation

Qore::Thread::AutoReadLock::constructor | ( | RWLock | rwl | ) |

Creates the AutoReadLock object based on the RWLock argument passed and immediately calls RWLock::readLock()

Creates the AutoReadLock object based on the RWLock argument passed. The AutoReadLock object immediately calls RWLock::readLock() on the RWLock object passed, and saves it so it can be released when the AutoReadLock object is destroyed.

Example:
  my AutoReadLock $arl($rwlock);

Exceptions

  THREAD-DEADLOCK | A deadlock was detected while trying to acquire the lock
  LOCK-ERROR | RWLock::readLock() called while already holding the write lock, object deleted in another thread, etc.

Qore::Thread::AutoReadLock::copy | ( |  | ) |

Throws an exception; objects of this class cannot be copied.

Exceptions

  AUTOREADLOCK-COPY-ERROR | objects of this class cannot be copied

Qore::Thread::AutoReadLock::destructor | ( |  | ) |

Calls RWLock::readUnlock() on the saved RWLock and destroys the AutoReadLock object.

Example:
  delete $arl;

Exceptions

  LOCK-ERROR | RWLock::readUnlock() called while not holding the read lock, RWLock object deleted in another thread, etc