Qore::Thread::AutoReadLock Class Reference

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

#include <QC_AutoReadLock.dox.h>

Public Member Methods
	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)
    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

constructor()

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:

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.

copy()

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

destructor()

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