Electrical computers and digital data processing systems: input/ – Access locking
Reexamination Certificate
2001-11-13
2004-06-08
Vo, Tim (Department: 2189)
Electrical computers and digital data processing systems: input/
Access locking
C710S220000, C709S241000, C707S793000, C707S793000
Reexamination Certificate
active
06748470
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to distributed computing environments and particularly to availability management of resources in a distributed environment. More particularly, the present invention relates to methods of “locking” distributed environment resources to prevent inappropriate access to such resources. More particularly still, the present invention relates to server-side management of locks within the WebDAV protocol.
BACKGROUND OF THE INVENTION
Distributed computer environments, such as computer networks, provide significant advantages to multiple computer clients or users. In particular, distributed environments allow multiple clients to actually share many different computer resources including both hardware and software resources. Sharing software-related resources provides many known benefits, such as the fact that only one such resource needs to be created, updated and maintained.
The Internet is one particular example of a distributed environment that provides access to a considerable number of software resources, which are available to practically any client computer system having Internet capabilities. One portion of the Internet is known as the World Wide Web which is a generally a system of Internet servers that house software related resources that are formatted in a particular manner, such as with HTML (HyperText Markup Language). The protocol for accessing these particular resources is known as the HyperText Transfer Protocol or HTTP. It should be noted however that not all Internet servers are part of the World Wide Web.
With recent advances, clients may effectively author resources on a server system from client systems over distributed networks, including the Internet. For instance, the WebDAV protocol or standard, which stands for the World Wide Web Distributed Authoring and Versioning standard, referred to herein as simply “DAV,” provides a set of headers and methods which extend HTTP to provide capabilities for managing properties, namespace and other items from a client system in order to allow client computer systems to access server-side resources for the purpose of editing those resources. Proposed Standard RFC 2518, which is a document written by the IETF and approved by the IESG, published February 1999, describes DAV in more detail.
As part of the DAV standard, server computer systems provide various services in managing the various access requests made by clients. One particular service relates to controlling when a resource is available for use by a client. That is, DAV provides methods that allow a client to lock a resource when using that resource so that subsequent users may not access that resource during that time. This locking scheme helps prevent the “lost update” problem associated with two or more users modifying a resource simultaneously such that editions are inadvertently lost. Additionally, the locking scheme provides an ability to lock two resources that may be needed to perform a file-management type function. For example, assuming a resource exists in one folder, yet the owner wants to move the resource into another folder, i.e., the destination folder. In such a case the client needs to lock both the resource and the destination folder. Locking both resources allows for the operation to proceed without conflicts.
Although the locks are helpful in preventing the lost update problem, the present locking system implemented in DAV is unsatisfactory with respect to the allocation of these locks. For instance, a DAV lock only covers, at most, one resource tree. That is, the lock request itself typically includes a uniform resource identifier (“URI”) and a depth. The depth indicates the number of levels of sub-elements or children of the resource identified by the URI to be locked. Unfortunately, if the client system needs to lock multiple URIs that are not in a parent child relationship, multiple lock requests are required. In return, the client system receives multiple lock tokens or cookies representing the locks on the various resources. Since many operations typically involve several different and unrelated resources, the request, receipt and management of the multiple locks increases the overhead involved.
Moreover, requesting multiple locks is not a satisfactory solution since some locks may be granted while others are not which negatively affects the atomicity of a requested operation. An atomic operation or the atomicity of an operation, relates to an operation that must be performed entirely or not at all. Since lock requests are typically associated with a particular access or command request, atomicity is typically required. Therefore, the partial granting of a selective few of the locks is not acceptable.
Additionally, if two or more separate client processes attempt to lock the same resources, a potential deadlock situation may occur, where each locks one of the resources but prevents the other(s) from locking all the resources. A deadlock situation precludes lock success for each of the processes. One solution to this problem involves a server-side utility that monitors lock requests and attempts to “remember” whether a lock request has been granted to a client process that is now requesting a subsequent resource. Recognizing that a client process is requesting a subsequent resource provides the server the ability to anticipate potential deadlock situations before they occur. Unfortunately, a significant amount of overhead is required to store information related to all previously granted lock requests, and the client that requested the lock.
It is with respect to these and other considerations that the present invention has been made.
SUMMARY OF THE INVENTION
The present invention solves these problems by creating and enabling the use of a new lock type request relating to multiple locks, i.e., multiple resources. The method and system creates and maintains lock properties for a resource or object in a distributed environment.
In accordance with certain aspects, the invention relates to a system and method of locking resources that receives a request to access more than one resource, wherein the request originates from a requesting client computer system and based on this request locks the requested resources. Upon locking the resources, the system and method provides a lock token related to the created lock to the requesting client computer system. The system and method may either create a new lock object for the resources or update and existing lock object. Thus, a plurality of resources may be locked based on one request. Additionally, since one request included an indication that more than one resource is to be locked, the receiving system can anticipate and resolve potential deadlock situations.
In accordance with other aspects, the system and method determining whether the resources are locked by one or more other client computer systems and locks the resources only if no existing lock conflicts with the type of access requested or the type of lock requested. When an existing lock is to be modified, the system and method may also determine whether the resources are locked by one or more other client computer systems or whether the requesting application is the lock owner and update a lock only if no existing lock conflicts with the type of access requested or the type of lock requested and if the requesting application is the owner. Further, prior to creating or updating the lock, a determination may be made as whether the other resources should be locked; and if other resources should be locked; then the system and method locks those resources.
In accordance with still other aspects, the present invention relates to a lock management system that has a receive module for receiving a request to lock a plurality of resources; a locking module for locking the requested resources; and an allocation module for allocating a lock token related to the requested resource. The lock management system may create or update a lock object that locks the plurality of resources. The lock object itself is
LandOfFree
Method and system for locking multiple resources in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for locking multiple resources in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for locking multiple resources in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3365420