Patent Application
20080046785
As illustrated in
This invention discloses a computer software “timeout algorithm” program 1 that reduces the amount of “timeout list” 130 manipulation (and therefore processing resources) needed to satisfy system or network requirements for scheduling and cancelling “timeout requests” 110 to determine whether the “timeout” (or expiration) time has been reached for execution of an input/output (I/O) request 100, thereby requiring a “timeout action” 120 to cancel the I/O operation if it has not yet been completed. As illustrated in
A UserThread 10 is programmed to accomplish the following processing functions: (i) a TimeOutRequest object 11 is created when a “timeout entry” 110 is originated upon initiation of an I/O request 100 and then placed into an “unordered queue” 132 with its “timeout status flag” 111 set to ACTIVE for a pending I/O request; (ii) a TimeOutRequest object is then invalidated by resetting its timeout status flag to CANCELLED when a timeout entry is no longer needed because its associated I/O request has been timely completed or if its timeout period has expired and a timeout action has been invoked.
A TimeOutRequest object 11 consists of definition of at least the following data fields for each individual timeout entry 110: (i) a timeout time 2 for which the timeout action will be invoked to cancel the read/write (or other) I/O operation 100 if it has not been completed by then (which can be the same length or duration for multiple timeout entries); (ii) identifying a “timeout action callback routine” should execution of a timeout action 120 be required for that entry; and (iii) setting a timeout status flag 111 as ACTIVE for an individual timeout request 110 if its associated I/O request 100 has not yet been executed and its timeout time 2 has not yet been reached, or CANCELLED if a timeout request is no longer valid due to timely completion of its I/O request or expiration of its timeout period and the subsequent invocation of a timeout action.
A TimeOutThread 12 processes the “timeout buckets” 131 and timeout lists 130 (including the unordered queue 132) and is programmed to accomplish the following processing functions, in order to eliminate the need for these data structures to be protected by “synchronization logic” since they will be accessed by only this thread: (i) an individual TimeOutRequest object 11 is removed from the unordered queue and it is ignored if this timeout request 110 has already been cancelled, and this processing step is then revisited for the next TimeOutRequest object in the queue; otherwise (ii) the point in time is calculated when that request should signal a timeout action 120 by adding the unelapsed portion of the timeout period 2 for that request to the initiation time of its associated I/O request 100 (which can be the current chronological time) and then adjusting the timeout action to take place at the nearest time interval or increment after that time (such as by “rounding up” to the nearest second or multiple of 1024).
The list of timeout buckets 131 is then searched for one that has the same adjusted timeout time 2 as the timeout request 110 under examination from the unordered queue 132, and if one is found then the request is inserted into that bucket from the unordered queue; otherwise, a new bucket is created with this new timeout time and the timeout request is assigned to that bucket (which can hold either a fixed or varying number of entries). The list of timeout buckets is ordered from “lowest” (soonest upcoming) timeout time to “highest” (most distant future) timeout time, so that a new bucket is inserted at that point in the list after a bucket that has a lower (and before a bucket that has a higher) timeout time than its own, so that each bucket represents the correct point in time for occurrence of the timeout with respect to each timeout request in that bucket. This processing step is then revisited for the next TimeOutRequest object 11 in the queue, and if there are no more timeout requests stored in the queue then the next processing step is executed.
The current chronological clock time is determined from the system and each timeout bucket 131 is periodically retrieved for examination according to its order from “lowest” timeout time to “highest” timeout time. The system chronological time is then compared to the timeout time 2 for the next bucket. If the timeout time has been passed then each timeout entry in the bucket is examined, and the TimeOutThread 12 triggers the timeout callback routine to initiate a timeout action 120 for the entry if it has not already been CANCELLED due to timely completion of its associated I/O request 100. (It should be noted that the timeout callback routine must in some instances be synchronized with the timeout status flag 111 to ensure that the I/O operation is not being completed at essentially the same time when the “timeout” is detected.) The bucket is then discarded after examining each of its timeout entries in this manner. Once a bucket is encountered for which the timeout time has not been reached, then no more buckets are examined through that cycle because each subsequent bucket will also have a timeout time that has not been reached. Therefore the next processing step will be executed. The “pruning” processing step is then executed after the last timeout bucket is examined using this step.
A “dead bucket pruning time interval” is defined to determine how often each-timeout bucket list 131 should be examined to decide if a bucket can be discarded. If this time interval has been triggered then each bucket is examined to determine whether all of its timeout entries 110 have been invalidated. If at least one timeout entry is still ACTIVE then the next bucket is examined, since all entries have not yet “timed out” for that bucket (meaning that it cannot yet be discarded). If all entries in a timeout bucket have already been invalidated, then its entries are discarded and the bucket is eliminated. The timeout algorithm 1 is inactivated for a certain period of time (i.e., “sleeps for a lazy interval”) to allow data processing to be accomplished instead of timeout processing. The timeout algorithm is then repeated in its entirety after expiration of this “lazy sleep interval” time period.
While certain preferred features of the invention have been shown by way of illustration, many modifications and changes can be made that fall within the true spirit of the invention as embodied in the following claims, which are to be interpreted as broadly as the law permits to cover the full scope of the invention, including all equivalents thereto.
