Abstract:
Method and apparatus for updating user data from multiple data sources in a data gateway are disclosed. The data gateway includes a persistent job table for centrally storing jobs to be processed by the plurality of servers, a server table for centrally storing statuses of activities of the plurality of servers, and a job engine for processing job requests from the multiple data sources using the persistent job table and the server table. The data gateway includes a server farm having a plurality of servers, and where both the persistent job table and the server table reside outside the plurality of servers. The data gateway further includes a virtual Internet Protocol load balancer for dynamically mapping of jobs to be processed to particular servers according to user identifiers.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of data communication over the Internet. In particular, the present invention relates to a data gateway.  
       BACKGROUND OF THE INVENTION  
       [0002]     The recent proliferation of electronic devices for communication, information management and recreation has moved routine computing power away from the desk-bound personal computer. Users are using devices such as cell phones, camera phones, personal digital assistants (PDAs) and navigation systems, not only in the office and in the home, but also in the field and on the road. There is a diverse range of possible applications for such devices, including communication, business, navigation, entertainment and even managing basic daily activities. Many users today only use a single device for a single task, for example, using cell phones for making and receiving phone calls. However, these devices are no longer single-function devices. They are capable of creating various types of data, for instance, electronic mail, voice messages, photos, video, etc. Increasing the number of functions of a device increases the level of personalization to the users. It is desirable to provide users a connected-service to connect and access their data wherever they are, with whatever device they are using and whatever service they are connected to.  
         [0003]     A conventional data gateway for handling millions of user devices with different data sources, such as IMAP, POP, WebDAV Exchange, is by employing a server farm with multiple gateway servers. Each gateway server in the server farm maintains a persistent storage for handling job requests of updating changes of users&#39; data. However, this conventional data gateway has a number of problems. One of the problems of the conventional data gateway is to provide failover support. When a server in the server farm fails or is inactive for a period of time, the system needs to transfer the job requests assigned to the failed server to other servers in the farm without losing the job requests. Thus, there is a need for a system that can transfer job requests from a failed server to other servers in the farm seamlessly.  
         [0004]     Another problem of the conventional data gateway is to provide a scalable system to support a growing user base. When a particular server farm runs out of capacity, it would be difficult to transfer the persistent storage of job requests to a new server farm as the job requests stored in the persistent storage may be at different stages of processing. Thus, there is a need for a system that can scale as the user base grows.  
         [0005]     Yet another problem of the conventional data gateway is to process job requests in an efficient manner. Since a user&#39;s job requests are not consistently sent to a particular server in the server farm, the user&#39;s account data need to be transferred and cached in multiple servers where the job requests are processed, which leads to additional use of data gateway resources. Therefore, there is a need for a system that can consistently send a user&#39;s job requests to a particular server such that the user&#39;s account data may be cached and efficiently used for subsequent job requests from the user.  
       BACKGROUND OF THE INVENTION  
       [0006]     In one embodiment, a data gateway for updating user data from multiple data sources includes a persistent job table for centrally storing jobs to be processed by the plurality of servers, a server table for centrally storing statuses of activities of the plurality of servers, and a job engine for processing job requests from the multiple data sources using the persistent job table and the server table. The data gateway includes a server farm having a plurality of servers, and where both the persistent job table and the server table reside outside the plurality of servers. The data gateway further includes a virtual Internet Protocol load balancer for dynamically mapping of jobs to be processed to particular servers according to user identifiers.  
         [0007]     In another embodiment, a method for updating user data from multiple data sources in a data gateway includes receiving a job request at the data gateway, fetching jobs due for processing from a persistent job table, sending the jobs to a storage queue, rescheduling the jobs in the persistent job table for processing at a future time, dispatching a job to be processed from the storage queue to a job handler, and processing the job by the job handler according to a data source type of the job. The data gateway includes a server farm having a plurality of servers. The persistent job table stores jobs to be processed by the plurality of servers and resides outside the plurality of servers.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The aforementioned features and advantages of the invention as well as additional features and advantages thereof will be more clearly understandable after reading detailed descriptions of embodiments of the invention in conjunction with the following drawings.  
         [0009]      FIG. 1  illustrates a gateway farm of servers supported by a virtual Internet Protocol load-balancer according to an embodiment of the present invention.  
         [0010]      FIG. 2  illustrates a data source gateway according to an embodiment of the present invention.  
         [0011]      FIG. 3  illustrates a block diagram of the data source gateway job engine according to an embodiment of the present invention.  
         [0012]      FIG. 4  illustrates a sequence diagram of timer-driven job scheduling according to an embodiment of the present invention.  
         [0013]      FIG. 5  illustrates a sequence diagram of a job dispatcher according to an embodiment of the present invention.  
         [0014]      FIG. 6  illustrates a hierarchical gateway job-locking scheme according to an embodiment of the present invention. 
     
    
       [0015]     Like numbers are used throughout the specification.  
       DESCRIPTION OF EMBODIMENTS  
       [0016]     The following descriptions are presented to enable any person skilled in the art to make and use the invention. Descriptions of specific embodiments and applications are provided only as examples. Various modifications and combinations of the examples described herein will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the examples described and shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.  
         [0017]     Some portions of the detailed description which follows are presented in terms of flowcharts, logic blocks, and other symbolic representations of operations on information that can be performed on a computer system. A procedure, computer-executed step, logic block, process, etc., is here conceived to be a self-consistent sequence of one or more steps or instructions leading to a desired result. The steps are those utilizing physical manipulations of physical quantities. These quantities can take the form of electrical, magnetic, or radio signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. These signals may be referred to at times as bits, values, elements, symbols, characters, terms, numbers, or the like. Each step may be performed by hardware, software, firmware, or combinations thereof.  
         [0018]      FIG. 1  illustrates a gateway farm of servers supported by a virtual Internet Protocol load-balancer according to an embodiment of the present invention. In this case, a gateway farm  102  is a group of server machines running the Data Source Gateway, Content Router, and SyncML server components. The Content Router is described in U.S. application Ser. No. ______ (attorney docket number 32421-2000900), entitled “Content Router,” to Torsten Schulz et al., which is hereby incorporated by reference in its entirety. The SyncML server is described in U.S. application Ser. No. ______ (attorney docket number 32421-2002800), entitled “Data Synchronization and Device Handling,” to Yang et al., which is hereby incorporated by reference in its entirety.  
         [0019]     Jobs to be processed by the gateway farm  102  of servers are received through a virtual Internet Protocol load balancer (VIP)  104 , which serves as a front-end interface for the gateway farm. The gateway farm  102  may include one or more gateway servers  106 . In addition, the gateway farm  102  is supported by a data source gateway (DSGW) persistent job table  110  and a gateway server table  112 . The VIP performs load-balancing requests from client devices to a cluster of machines running behind the VIP load-balancer, where IP means the Internet Protocol address of a machine.  
         [0020]     A P_Value is a hash value that is computed from the user&#39;s login, such as from a Yahoo ID. This value is computed and padded to a length of 24 characters. The VIP uses this value to create a mapping from the P_Value to a particular gateway host. If a mapping exists, it assigns all jobs with a given P_Value to the corresponding host in the mapping table. The P_Value is generated when the default (primary account where data is aggregated) user account is provisioned. When a new data account (like POP, WebDAV Exchange, etc) is added, a P_Value of the primary account is assigned to it. The P_Value is part of requests received from client devices to the gateway farm. The VIP for the gateway farm is configured to search for a name that matches the name value pair in the HTTP query string. It searches for a string “p=” followed by 24 characters. It uses this value to compute the P hash and assigns the request to an appropriate gateway server behind the VIP.  
         [0021]     Note that as long as the servers behind the VIP in the gateway farm are up and running, and are not heavily loaded, it is guaranteed that requests for a given user are directed to and handled by the same machine in the server farm. This method provides at least two advantages. First, since all the requests for a given user are handled by the same machine, job information for the user can be cached on that machine, thus the performance of handling user requests may be improved. Second, in case of handling failover of a gateway server in the gateway farm, it is guaranteed that the repeated or recurring jobs are handled by the same server machine as new notifications received from client devices.  
         [0022]     In one embodiment, the VIP implements a gateway job scheduling algorithm that ensures partitioning of the user cache and Open Systems Interconnection (OSI) layer-7 stickiness. The OSI for computer communications supports a 7-layer model as listed: Application, Presentation, Session, Transport, Network, Data Link, and Physical. The Transport layer is the layer that provides reliable communication between two systems. The layers above the Transport layer can assume that they have an error-free communications link. The Presentation layer relates to the representation of data that is being exchanged between two systems. The Session layer provides services to applications running about it. Two of the important services it provides are establishing a session and releasing a session. The Application Layer (Layer-7) is used to communicate application data between two systems. Examples of the Application Layer are Electronic Mail, Directory Services, Virtual Terminal, File Transfer, etc.  
         [0023]     The Layer-7 stickiness ensures that devices and clients communicating with the connected data source gateways are not suddenly shifted from one gateway server to the other in the gateway server farm by the VIP. This guarantees that during a session a device/client will go to the same gateway host in the farm. This allows the gateway to cache information on a particular gateway for a given user or device thus improving the performance and balancing the processing/data load on the gateways in the farm. The P_Value, which is included in every request sent to the gateway, is used in maintaining the layer-7 stickiness and load-balancing of the data synchronization job requests. This includes jobs that come from outside the system (for example data change notifications from devices and/or registered data sources) and jobs that get rescheduled from the gateway job table, such as recurring jobs and delayed jobs (for example job delayed due to temporary error or as a result of the appropriate lock not being available).  
         [0024]     Therefore, the P_Value, Layer-7 stickiness and the VIP are employed to ensure 1) high availability of the data gateway by automatically bypassing gateway servers that are down and thus ensuring that a user never experiences a service down time; 2) intelligent load-balancing of the data gateway by routing requests to those servers that have processing bandwidth; and 3) session stickiness by guarantee that a given user/device requests are handled on the same gateway in the farm no matter where they come from.  
         [0025]     The following example further describes the functions of the VIP discussed above. Initially, all three gateway machines (Gateway1, Gateway2 and Gateway3) are assumed to be up and running with the following P_Value and gateway host mapping in the VIP. The P_Value specifies the P-hash value computed from the Yahoo ID of the primary data source account for a given user account, and the Gateway Host specifies the gateway host that is the current owner of the job.  
                   TABLE 1A                       P_Value   Gateway Host                   P1   Gateway1       P2   Gateway2       P3   Gateway3       P4   Gateway1       P5   Gateway2                  
 
         [0026]     As shown in Table 1A, Gateway1 handles jobs for users with P_Values P1 and P4; Gateway2 handles jobs for users with P_Values P2 and P5; and Gateway3 handles jobs for users with P_Value P3.  
         [0027]     Next, assume that Gateway1 goes down and does not come back up for a predetermined period of time. In this case, the VIP performs load-balancing and modifies the P_Value to Gateway Host mapping as follows.  
                   TABLE 1B                       P_Value   Gateway Host                   P1   Gateway3       P2   Gateway2       P3   Gateway3       P4   Gateway2       P5   Gateway2                  
 
         [0028]     As shown in Table 1B, Gateway2 handles jobs for users with P_Values P2, P4 and P5, and Gateway3 handles jobs for users with P_Values P3 and P1. In this case, the Gateway2 and Gateway3 update the VIP mapping (P_Value to Gateway host) they infer when they receive a new request via the VIP from a device or data source.  
         [0029]     Next, assume that Gateway1 comes back up after a certain period of time. The VIP updates the (P_Value to gateway host) mapping when it performs load-balancing, assuming the following are resulted in the VIP after mapping.  
                   TABLE 1C                       P_Value   Gateway Host                   P1   Gateway3       P2   Gateway2       P3   Gateway1       P4   Gateway2       P5   Gateway1                  
 
         [0030]     In this case, Gateway1 handles jobs for users with P_Values P3 and P5; Gateway2 handles jobs for users with P_Values P2 and P4; and Gateway3 handles jobs for users with P_Values P1. Note that Gateway1, Gateway2 and Gateway3, respectively, update the VIP mapping they infer based on requests received via the VIP (from devices and data sources).  
         [0031]     The method ensures the network layer-7 stickiness established by the VIP is maintained when processing jobs in the gateway farm. There are at least three advantages. First, it guarantees that new job requests received from outside (from devices or data sources) and rescheduled jobs in the gateway farms will be handled by the same gateway host. This improves the efficiency of job handling because the method takes advantage of user information that may already be cached on a dedicated gateway host. Second, it prevents cached user data from spreading across the gateway farm servers, thus reduces memory usage and improves performance of the data source gateway. Third, the method ensures proper load-balancing for failover support and it improves the scalability of the system.  
         [0032]     Table 1D shows an example of a job table that maintains the jobs to be processed by the data source gateway.  
                               TABLE 1D                       UserID   P_Value   Job   GatewayHost   Timestamp                   User1   P1   Mail   Gateway3   1347103427       User2   P2   Calendar   Gateway2   1431234137       User3   P3   AddressBook   Gateway1   1453241323       User1   P1   Mail.LongPoll   Gatway3   1432342322       User2   P2   Mail.LongPoll   Gateway2   1312222222                  
 
         [0033]     In this case, when the gateway receives a job request via the VIP, it determines whether there is a mapping from the P_Value to a particular gateway. If such mapping does not exist, it creates a new mapping. If such a mapping exists, the job scheduler makes a second determination whether the mapping has changed. If the mapping has not changed, the job scheduler continues processing this job. If the mapping has changed, the job scheduler updates the mapping and changes the gateway host entry for all rescheduled jobs in the persistent job table store. This ensures that the gateway infers dynamic VIP mapping of the P_Values to establish layer-7 stickiness with the new servers. As a result, the subsequent jobs of the same users are sent to the same new servers for processing via the VIP.  
         [0034]     Table 1E illustrates the use of parameters RetryCount and RescheduleFlag in the persistent job table according to an embodiment of the present invention and the parameters of the persistent job table are described below:  
                                       TABLE 1E                           Datasource   Job       Retry               ExtUserID   Type   Type   Server   Count   Due Time   Reschedule                   User1   Yahoo   Mail   Gateway1   0   1131993562971   0       User1   Yahoo   Calendar   Gateway1   0   1131994101734   0       User2   Exchange   Mail   Gateway2   0   1131994101734   1       User3   IMAP   Mail-   Gateway2   0   1131993801595   0               Poll       User4   Yahoo   Calendar   Gateways   2   1131999801595   0                 Persistent_Job_Table (ExtUserID, DatasourceType, JobType, Server, RetryCount, DueTime, RescheduleFlag) Where            ExtUserID: is a unique ID identifying a given user&#39;s entries in the job table.            DatasourceType: specifies the data source account (example: YAHOO, Exchange, IMAP, POP etc)            JobType: specifies the gateway data synchronization jobs. Examples are Mail, Calendar, AddressBook, Mail-poll, Calendar-poll, etc.            Server: specifies the gateway server currently owning the job.            RetryCount: is the number of times the gateway has tried processing this job as a result of temporary error.            DueTime: specifies the next time this job needs to be processed.            RescheduleFlag: indicates the gateway has received another notification for a job that is currently being processed.             
 
         [0035]     Note that the purpose of the RetryCount is to ensure that jobs that fail often due to temporary errors do not monopolize the gateway resources. This parameter is used by the job dispatcher to reschedule the job with an incremental delay. This ensures that all jobs have a fair opportunity in getting processed. Also, when the RescheduleFlag is set, the gateway may reschedule the job. This flag ensures that any change notification the gateway received will not be lost.  
         [0036]      FIG. 2  illustrates a data source gateway according to an embodiment of the present invention. The data source gateway includes a Content Router API  204 , Java Mail API  206 , WebDAV API  208 , and a data source gateway (DSGW) job engine  212 . The Java Mail API  206  includes IMAP4 adaptor  214 , MSN adaptor  216 , and POP3 adaptor  218  for communicating to IMAP4 server  215 , MSN server  217 , and POP3 server  219 , respectively. The WebDAV API  208  includes an MS Exchange adaptor  220  for communicating with an Exchange server  221 . The DSGW job engine  212  provides the logic for accessing data sources. The data source gateway inventory includes a list of data source accounts, folder, and folder item information and individual data type information, such as mail, PIM, etc. The folders may be mail or PIM folders. This information is accessed by the DSGW job engine  212  to determine the data synchronization state when servicing a request for data from the data source. The gateway server table  112  includes a list of gateway servers and their corresponding last job schedule timestamps for that server. The gateway uses the settings exchange (SETEX) API  222  to exchange the folder list and meta-data information with the Content Router. On the other hand, new mail and PIM information are exchanged with the Content Router using the records exchange (REX) API  224 . Attachments are sent using the commands exchange (CEX) API  226  to the Content Router. These accounts are accessed by the gateway module when processing incoming mail meta-data modifications (folder filing, read status, etc), and new mails from the device are delivered back to the mail gateway and forwarded to the mail data source accordingly. In other embodiments, additional message body and attachment tables may be introduced to allow attachments and full bodies to be delivered to devices without additional communications with the mail servers.  
         [0037]      FIG. 3  illustrates a block diagram of the data source gateway job engine according to an embodiment of the present invention. As shown in  FIG. 3 , the DSGW job engine includes a change notification handler  302 , a job scheduler  304 , a job dispatcher  306 , a job handler  308 , a JMS queue  310 . In addition, the DSGW job engine communicates with the DSGW persistent job table  110  and the gateway server table  112 .  
         [0038]     Jobs may be added to the DSGW job engine via the change notification handler  302 . The change notification handler  302  can receive change notification requests from the devices or from registered backend data sources (YAHOO, IMAP, POP, WebDAV Exchange, etc). In each of these cases, the change notification handler  302  adds jobs to be consumed by the job dispatcher to the JMS queue  310  (to be dispatched for processing) and reschedule them for re-processing at a later time as an assurance against job loss due to a server crash or a server internal error in a distributed server environment. The JMS queue is a first-in-first-out (FIFO) memory storage device. Another way jobs are added to the DSGW job engine is via the job dispatcher  306 , which reschedules repeated jobs and delayed, which include jobs that failed due to a temporary error or jobs that were not processed since an appropriate data type lock was not available.  
         [0039]     The job scheduler  304  schedules a change request job by adding it to the JMS queue  310 . These jobs are picked up by the job dispatcher  306  and dispatched to the appropriate job handler  308  for processing the change request. After the job handler completes processing the change request, it returns a job completion status to the job dispatcher. If the job is successfully completed and it is not a recurring job, it is then removed from the DSGW persistent job table. On the other hand, if the job is a recurring job or if the job handler returns a busy or temporary status, the job is then rescheduled in the DSGW persistent job table  110  for processing at a later time. The job scheduling and dispatch process is further explained in the following sections.  
         [0040]     The job scheduler schedules jobs in one of two ways. One way is by picking-up jobs from the DSGW persistent job table  110  when it is triggered periodically by the timer  314 , which is also known as timer-driven job scheduling. Another way is triggered by the change notification handler  302  to process change notifications from the devices and from registered data sources.  
         [0041]      FIG. 4  illustrates a sequence diagram of timer-driven job scheduling according to an embodiment of the present invention. In this case, the gateway job engine handles the processing of recurring jobs and delayed jobs, which include jobs rescheduled as a result of temporary error, jobs delayed since a lock was not available for a given data type, or jobs not processed as a result of server crash. The steps shown in  FIG. 4  are further described below: 
        1. The gateway job engine timer goes off at periodic intervals and triggers the job scheduler.     2. The job scheduler queries the persistent job table for all the jobs that are due or overdue for processing for which it is the owner.     3. The selected jobs are added to the first-in-first-out (FIFO) JMS Queue and are also rescheduled in the persistent job table for processing at a future time as an assurance against job loss due to server crash or server internal error.     4. Jobs added to the JMS Queue are picked up in a first-in-first-out order by the job dispatcher.     5. The job dispatcher then dispatches each job to an appropriate job handler based on the data source type.     6. The job handler processes each job and returns a completion status to the job dispatcher.     7. If the status returned indicates the job has been completed, the job dispatcher removes the job from the persistent job table if it is a one-time job and reschedules the job if it is a recurring job.     8. If the status returned indicates a busy-lock taken, the job is delayed for processing at a later time.     9. If the job completion status returned indicates a temporary error, the job dispatcher increments the retry count and reschedules the job with an exponential delay to prevent a job from excessive use of the gateway resources.          
         [0051]     The DSGW persistent job table  110  is a centralized persistent job store that is essential for preventing job loss and enabling job failover support in the data source gateway. There is one such persistent job table for each gateway farm, which includes multiple load-balanced gateway servers behind a VIP. The job scheduler also adds jobs to the persistent job table with a delayed reschedule time when adding jobs to the JMS queue as an assurance against job loss. This step ensures that even if the data source gateway crashes or is overloaded, the jobs are picked-up by other gateway servers in the farm, thus giving the end-user an un-interrupted data synchronization service.  
         [0052]     The following steps describe the job scheduler uses the gateway server table in handling failover of a server according to an embodiment of the present invention. 
        1. The gateway job scheduler running on a particular gateway is periodically triggered to pick-up jobs for which it is the current owner and that are due or overdue for processing from the persistent job table.     2. It then updates the last job reschedule timestamp for the current gateway in the gateway server table. This step is used for failover support.     3. It schedules the jobs in the JMS queue for processing and also reschedules the jobs in the persistent job table for processing at a later time. This step is an assurance against job loss due to server crash or internal errors.     4. The job scheduler then queries the gateway server table to retrieve a list of all gateway servers that have not updated their last job reschedule timestamps within the failover time interval. The gateway servers that have not updated the timestamps within the failover interval are referred to as inactive servers.     5. The job scheduler then picks up the jobs that are due and owned by the inactive servers and reschedules them via the VIP specifying the P_Value for each rescheduled job. This ensures that the failover jobs will be processed on the same gateway as new jobs being sent via the VIP to a corresponding gateway thereby maintaining layer-7 stickiness of the jobs to be processed.        
 
         [0058]     The change notification handler  302  schedules jobs by invoking the job scheduler  304  when it receives change notifications from client devices or from registered data source servers, such as Yahoo, IMAP, POP or WebDAV Exchange. The change notification jobs are then added to the JMS queue  310  and are also added to the DSGW persistent job table  110  to be processed at a later time. In this case, the jobs are added to the DSGW persistent job table to ensure recovery in the event of server crash or unavailability of the data source server.  
         [0059]      FIG. 5  illustrates a sequence diagram of a job dispatcher according to an embodiment of the present invention. The sequence diagram describes the process for dispatching a DSGW job, which is a data synchronization job, to keep the data between the devices and the target data sources in synchronization to the appropriate data source gateway component for further processing. The steps shown in  FIG. 5  are described below: 
        1. The gateway change notification handler receives a data change notification from a device (such as a PDA). The data changed may be new mails to be sent, mail flag changes, new PIM data, etc. Alternatively, the gateway change notification handler may receive a data change notification request from a backend data source (such as Yahoo Mail, Yahoo Calendar etc). The data changed may be new mails, deleted mails, change in flags, etc.     2. The change notification handler invokes the job scheduler to schedule the job for processing.     3. The job scheduler first adds the job request to the persistent job table as an assurance against job loss.     4. The job scheduler then adds the job to the JMS Queue for processing by the job dispatcher.     5. The job dispatcher picks up the jobs from the JMS queue in a first-in-first-out order.     6. The job dispatcher obtains an appropriate lock for the job to be processed and dispatches it to an appropriate job handler based on the data source type.     7. The job handler processes the job and returns the completion status to the job dispatcher.     8. If the status returned indicates the job has been completed, the job dispatcher removes the job if it is a one-time job and reschedules the job at an appropriate time interval if it is a periodic recurring job.     9. If the status returned indicates a busy-lock taken, the job is delayed for processing at a later time and the persistent job table is updated.     10. If the job completion status returned indicates a temporary error, the job dispatcher increments the retry count and reschedules the job with an exponential delay to prevent a job from excessive use of the gateway resources.          
         [0070]     The job handler  308  processes the change notification or data synchronization job dispatched by the job dispatcher  306 . It uses the information received in the dispatched job to invoke an appropriate job handler to complete processing the data synchronization job with the backend data source servers. The job handler further implements a hierarchical gateway job-locking scheme to enable concurrency while maintaining data integrity when processing jobs for different data types (for example mail, calendar, etc) of the same data source type (for example Yahoo, Exchange, and IMAP). The hierarchical gateway job-locking scheme is further explained with the help of various lock-request scenarios.  
         [0071]      FIG. 6  illustrates a hierarchical gateway job-locking scheme according to an embodiment of the present invention. As shown in  FIG. 6 , the hierarchical gateway job-locking scheme implements a multi-tier locking mechanism with an Account lock  602  as a parent in tier one, and multiple DataType locks as children of the Account lock at tier two. Note that there can only be one Account lock per data source account. An Account lock is used to obtain a mutually exclusive write access to perform an update of the user&#39;s account information. Examples of account jobs are: 1) provision user account, 2) update user account configuration, 3) delete user account, and 4) de-activate user account.  
         [0072]     The data source gateway supports multiple DataType locks per account, one for each data type (for example mail, calendar, etc) supported by the data source type (such as Yahoo, Exchange, IMAP, and POP). In this case, the DataType locks include mail lock  604 , sendmail lock  606 , calendar lock  608 , addressbook lock  610 , task lock  612 , and photo lock  614 . Taking a DataType lock is equivalent to taking a read lock on the parent Account lock at tier1, and a write lock on the specific DataType lock, for example mail lock, calendar lock, and addressbook lock, at tier2.  
         [0073]     In one approach, an Account lock scheme includes the following parameters: (ExtUserID, AccJobType, AccServer, AccTimestamp, LockFlags), where 
        ExtUserID: is the unique user identifier that identifies the data source account.     AccJobType: is the account job that has taken the lock (e.g. provision)     AccServer: is the gateway instance that holds the Account lock (i.e. is the IP address of the gateway)     AccTimestamp: is the time when the Account lock was taken.     LockFlags: is a bitmap that specifies the list of locks already taken for the data source account.        
 
         [0079]     A DataType lock scheme includes the following parameters: (ExtUserID, LockType, JobType, Server, Timestamp), where 
        ExtUserID: is the unique user identifier that identifies the data source account.     LockType: identifies the class of the DataType lock (for example, Mail, Calendar, etc)     JobType: specifies the DataType job that has taken the lock (for example, Mail)     Server: is the gateway instance that holds the DataType lock (is the IP address of the gateway)     Timestamp: is the time when the Account lock was being taken.        
 
         [0085]     The following code describes a lock-fetch algorithm according to an embodiment of the present invention. Inputs to the lock-fetch algorithm are the request lockType (for example, Account, Mail, Addressbook) and the extUserID of the data source account.  
                                                                                                                                                                                                                         Synchronized (LockInventory)       {       lockEntry = fetchLockEntryFromInMemoryCache( );       if (lockEntry == null)                lockEntry = new placeHolderLockEntryInMemoryCache( )            }       Boolean lockExpiredFlag = false;       Synchronized (lockEntry)       {                GetAnExclusiveAccessToDistributedDataSourceAccountLockEntry           {                if (lockIsTaken)           {                lockExpiredFlag = checkIfLockExpired(lockEntry);           if (lockExpiredFlag == true)           {                Break existing lock           Grant lock for current request           Update lock inventory.           Update local Cache           Return lockGranted                }           else           {                If (requestLockType == Account)           {                Mark Account-pending in lock inventory           Update Account-pending info in lockEntry.           Return lockDenied                }           Else//Deals with locks taken by a particular data type                Return lockDenied                }                }           else           {                lockTakenFromInv = Select for update for lock info in gateway inv.           if (lockAvailable)           {                Grant Lock           Update lock inventory.           Update local cache.           Return lockGranted                }                }                }            }       }                  
 
         [0086]     Table 2 lists various locking scenarios. For each locking scenario, this section describes a set of cases when the first lock-fetch request is received. In Table 2, 0 indicates the lock is available, and 1 indicates the lock is taken.  
                                                             TABLE 2                                       LockFlags Field                Account-           Send-   Address-                   Locking Scenario   pending   Account   Mail   mail   book   Calendar   Tasks   Photo               No-locks-held   0   0   0   0   0   0   0   0       Account-lock-is-held   0   1   0   0   0   0   0   0       No-locks-held and   1   0   0   0   0   0   0   0       Account-lock-request-       is-pending       DataType-locks-held   0   0   1   0   1   1   0   1       and no-account-lock-       request-is-pending       DataType-locks-held   1   0   1   0   1   0   0   1       and Account-lock-is-       pending                  
 
         [0087]     In the no-locks-held case, the first Account lock request made is granted. The first DataType lock for each data type (Mail, Sendmail, Addressbook, etc) is granted. In the Account-lock-is-held case, if an Account lock request comes in, it will be denied and the Account-pending flag will be marked. In addition, all accesses to DataType locks will be denied. In the no-locks-held and Account-lock-request-is-pending case, if an Account lock comes in, it will be granted and the pending flag will be cleared. All accesses to DataType locks will be denied.  
         [0088]     In the DataType-locks-held and no-account-lock-request-is-pending case, if an Account lock request comes in, it will be denied and the Account-pending flag will be set. On the other hand, if a DataType lock request comes in, the request will be denied if the data types match, and it will be granted if the data types do not match. For example, if a Mail lock is taken, and a request for another Mail lock comes in, the request will be denied. But requests for Calendar, Addressbook, etc will be granted as long as locks are not currently held for those data types.  
         [0089]     In the DataType-locks-held and Account-lock-is-pending case, if an Account lock request comes in, it will be denied and all DataType lock requests will be denied. The only exception in this case is a request for a data type lock by a higher priority job. When this happens, the gateway job dispatcher/handler breaks the existing lock and grants it to a higher priority job in the current context.  
         [0090]     As described above, the DSGW job engine enables distributed asynchronous job processing capability with at least the following functions: 1) eliminates job loss; 2) supports distributed asynchronous processing of jobs; 3) eliminates service down time by providing a job failover support in the event of a server crash or job overload; 4) ensures data integrity when synchronizing data with different data sources; and 5) improves the scalability.  
         [0091]     It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.  
         [0092]     The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors.  
         [0093]     One skilled in the relevant art will recognize that many possible modifications and combinations of the disclosed embodiments may be used, while still employing the same basic underlying mechanisms and methodologies. The foregoing description, for purposes of explanation, has been written with references to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described to explain the principles of the invention and their practical applications, and to enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.