Multiprocessing computer system with exit logic and method for maintaining resource integrity

Claim 1

A multiprocessing computer system in which each of a plurality of processes has access to at least one system resource, the multiprocessing computer system comprising: local count means for each process to maintain a count of permits for that process to access said resource; global count means to maintain a count of permits for all processes to access said resource; update logic for sequentially updating an appropriate local count means and the global count means each time a process requests or relinquishes use of the resource; exit logic for terminating a process including means for resetting the global count means, characterized in that: the local and global count means maintain a count of permits to read a resource; the update logic additionally comprises logic for storing expected local and global count values in first and second storage means respectively, before either of the appropriate local count means or the global count means are updated where the expected value of the local count stored in the first storage means is the current local read count plus an intended local count increment and the expected value of the global count stored in the second temporary storage means is the current global count plus an intended global count increment; and the exit logic additionally comprises logic for comparing the content of the first storage means to that of the appropriate local count means and for comparing the content of the second storage means to the global count means and, in dependence on the results of the comparisons, determining whether the process was terminated between the updating of the local and global count means.

Claim 10

A method of maintaining resource integrity in a multiprocessing computer system wherein a local variable which is accessible by a single process and a global variable which is accessible by a plurality of processes and is dependent on the local variable are updated sequentially, said local and global variables are read counts for maintaining a count of read access permits to a resource, and wherein the process may be terminated between the updating of the local and global variables, said method comprising the steps of: a) storing the expected value of the local variable in a first storage means and the expected value of the global variable in a second storage means where the expected value of the local variable stored in the first storage means is the current local read count plus an intended local read count increment and the expected value of the global variable stored in the second temporary storage means is the current global read count plus an intended global read count increment; and then b) updating the local variable and the global variable sequentially, and c) if said process is terminated, determining whether the process was terminated between the updating of the local and global variables by comparing the content of the first storage means to that of the local variable and by comparing the content of the second storage means to that of the global variable and, if necessary, undertaking remedial action to correct the values of the variables.

Claim 11

A method of maintaining resource integrity in a multiprocessing computer system wherein a local variable which is accessible by a single process and a global variable which is accessible by a plurality of processes and is dependent on the local variable are updated sequentially, said local and global variables are read counts for maintaining a count of read access permits to a resource, and wherein the process may be terminated between the updating of the local and global variables, said method comprising the steps of: a) storing the expected value of the local variable in a first storage means and the expected value of the global variable in a second storage means where the expected value of the local variable stored in the first storage means is the current local read count plus an intended local read count increment and the expected value of the global variable stored in the second temporary storage means is the current global read count plus an intended global read count increment; and then b) updating the local variable and the global variable sequentially, and c) if said process is terminated, determining whether the process was terminated between the updating of the local and global variables by comparing the content of the first storage means to that of the local variable and by comparing the content of the second storage means to that of the global variable and, if necessary, undertaking remedial action to correct the values of the variables.