Method and device for controlling timers associated with multiple users

Abstract

A system for providing a plurality of timers to perform the timing of event occurrences wherein, for each event, there corresponds a timer control block which stores in its time-flag field (Tf) an indication of whether the timer control block is chained or unchained, running or stopped, in its time-out field (Tv) the expiration time interval and in its time-stamp field (Ts) the current time as a reference at each interruption. The timer control blocks are chained by a one-way link according to their expiration times in such a way that each timer chain contains the timer control blocks whose events will occur at the same time. A cyclic table of index values classifies the timer chains according to their expiration times. When a START operation is requested for an event which has to occur at a time-out value, an index is computed according to the Tv and the current time in order to insert its corresponding timer control block at the head of the timer chain pointed to by the index; the timer control block storing the state of CHAINED-RUNNING in its time-flag and the current time in its time-stamp. If the timer control block is already chained, then the time-stamp is updated to the current time and the time-flag to RUNNING. Whenever a RESTART operation is requested for an event which has not occurred, the time-stamp of the corresponding timer control block is updated to the value of the current time. Whenever a STOP operation is requested before the event has occurred, the time-flag is updated to STOP. The time-stamps and the time-flags are updated according to the START, STOP and RESTART operations, the current index of the cyclic table is incremented at each timer-tick to delete the timer control blocks of the chain whose events have occurred or whose time-out values have expired, and to insert new timer control blocks in the new timer chain for those tasks which have been interrupted and whose events have not occurred yet.