Thread safety and NSMutableArray properties

[Robbie Hanson]

In AKSIPAccount, there is a property like this:

@property(readonly, retain) NSMutableArray *calls;

The property is used in various places such as AKSIPAccount's makeCallTo method, and also in AKSIPUserAgent's SIPCallByIdentifier method:

- (AKSIPCall *)SIPCallByIdentifier:(NSInteger)anIdentifier {

  for (AKSIPAccount *anAccount in [[[self accounts] copy] autorelease])

    for (AKSIPCall *aCall in [[[anAccount calls] copy] autorelease])

      if ([aCall identifier] == anIdentifier)

        return [[aCall retain] autorelease];

  

  return nil;

}

I believe this might be a problem.  Even though the property is atomic, this only means that it's atomic for getters and setters.  Modifying the mutable array from multiple threads is still unsafe.

As an alternative, one might consider removing the calls property, and adding thread safe methods to manipulate the array:

- (void)addCall:(AKSIPCall *)call
{
@synchronized(calls)
{
  [calls addObject:call];

}

}

- (AKSIPCall *)callByIdentifier:(NSInteger)callID
{
@synchronized(calls)

{

for(AKSIPCall *call in calls)

{

if([call identifier] == callID)

{

return [[call retain] autorelease];

}

}

return nil;

}
}

- (void)removeCall:(AKSIPCall *)call
{
@synchronized(calls)
{
  [calls removeObject:call];

}
}

- (void)removeAllCalls
{
@synchronized(calls)
{
  [calls removeAllObjects];

}
}

- (NSArray *)allCalls
{
@synchronized(calls)
{
  return [[calls copy] autorelease];

}
}

-Robbie Hanson

[Alexei Kuznetsov]

Thank you again, Robbie! Started issue 223.

Alexei