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Make llcache_object_notify_users robust to the object's user list changing underneath it 

svn path=/trunk/netsurf/; revision=11044
This commit is contained in:
John Mark Bell 2010-12-12 23:37:21 +00:00
parent 2e249ac9e6
commit 650f884527
1 changed files with 34 additions and 3 deletions
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37
content/llcache.c
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@ -1311,10 +1311,36 @@ nserror llcache_object_notify_users(llcache_object *object)
llcache_handle *handle = &user->handle;
const llcache_fetch_state objstate = object->fetch.state;
/* Save identity of next user in case client destroys
* the user underneath us */
/* Flag that this user is the current iteration target
* in case the client attempts to destroy it underneath us */
user->iterator_target = true;
next_user = user->next;
/* A note on the computation of next_user:
*
* Within this loop, we may make a number of calls to
* client code. Our contract with clients is that they
* can do whatever they like from within their callback
* handlers. This is so that we limit the pain of
* reentrancy to this module alone.
*
* One of the things a client can do from within its
* callback handler is to remove users from this object's
* user list. In the common case, the user they attempt
* to remove is the current iteration target, and we
* already protect against that causing problems here.
* However, no such protection exists if the client
* attempts to remove other users from this object's
* user list.
*
* Therefore, we cannot compute next_user up-front
* and expect it to remain valid across calls to
* client code (as the identity of the next user
* in the list may change underneath us). Instead,
* we must compute next_user at the point where we
* are about to cause another iteration of this loop
* (i.e. at the very end, and also at the points where
* continue is used)
*/
#ifdef LLCACHE_TRACE
if (handle->state != objstate) {
@ -1349,6 +1375,7 @@ nserror llcache_object_notify_users(llcache_object *object)
}
if (user->queued_for_delete) {
next_user = user->next;
llcache_object_user_destroy(user);
continue;
}
@ -1383,6 +1410,7 @@ nserror llcache_object_notify_users(llcache_object *object)
}
if (user->queued_for_delete) {
next_user = user->next;
llcache_object_user_destroy(user);
continue;
}
@ -1403,6 +1431,7 @@ nserror llcache_object_notify_users(llcache_object *object)
}
if (user->queued_for_delete) {
next_user = user->next;
llcache_object_user_destroy(user);
continue;
}
@ -1410,6 +1439,8 @@ nserror llcache_object_notify_users(llcache_object *object)
/* No longer the target of an iterator */
user->iterator_target = false;
next_user = user->next;
}
return NSERROR_OK;