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Diffstat (limited to 'scheduler/newselect.txt')
| -rw-r--r-- | scheduler/newselect.txt | 115 |
1 files changed, 115 insertions, 0 deletions
diff --git a/scheduler/newselect.txt b/scheduler/newselect.txt new file mode 100644 index 000000000..5cb9ab4ba --- /dev/null +++ b/scheduler/newselect.txt @@ -0,0 +1,115 @@ +Design Notes for New Poll/Select API in CUPSD - 2006-06-06 +---------------------------------------------------------- + +SUPPORTED APIS + + OS select poll epoll kqueue /dev/poll + -------------- ------ ------ ------ ------ --------- + AIX YES YES NO NO NO + FreeBSD YES YES NO YES NO + HP-UX YES YES NO NO NO + IRIX YES YES NO NO NO + Linux YES YES YES NO NO + MacOS X YES YES NO YES NO + NetBSD YES YES NO YES NO + OpenBSD YES YES NO YES NO + Solaris YES YES NO NO YES + Tru64 YES YES NO NO NO + Windows YES NO NO NO NO + + +HIGH-LEVEL API + + typedef void (*cupsd_selfunc_t)(void *data); + + void cupsdStartSelect(void); + void cupsdStopSelect(void); + void cupsdAddSelect(int fd, cupsd_selfunc_t read_cb, + cupsd_selfunc_t write_cb, void *data); + void cupsdRemoveSelect(int fd); + int cupsdDoSelect(int timeout); + + +IMPLEMENTATION STRATEGY + + 0. Common Stuff + a. CUPS array of file descriptor to callback functions + and data. + b. cupsdStartSelect() creates the array + c. cupsdStopSelect() destroys the array and all elements. + d. cupsdAddSelect() adds to the array and allocates a + new callback element. + e. cupsdRemoveSelect() removes from the array and frees + the callback element. + + 1. select() + a. Input/Output fd_set variables, copied to working + copies and then used with select(). + b. Loop through CUPS array, using FD_ISSET and calling + the read/ write callbacks as needed. + c. cupsdRemoveSelect() clears fd_set bit from main and + working sets. + d. cupsdStopSelect() frees all of the memory used by the + CUPS array and fd_set's. + + 2. poll() + a. Regular array of pollfd, sorted the same as the CUPS + array. + b. Loop through pollfd array, call the corresponding + read/write callbacks as needed. + c. cupsdAddSelect() adds first to CUPS array, then uses + current index to determine insertion point for pollfd + array. + d. cupsdRemoveSelect() needs to update cupsdDoSelect() + loop counter if <= current index. + e. cupsdStopSelect() frees all of the memory used by the + CUPS array and pollfd array. + + 3. epoll() + a. cupsdStartSelect() creates epoll file descriptor using + epoll_create() with the maximum fd count, and + allocates an events buffer for the maximum fd count. + b. cupsdAdd/RemoveSelect() uses epoll_ctl() to add + (EPOLL_CTL_ADD) or remove (EPOLL_CTL_DEL) a single + event using the level-triggered semantics. The event + user data field is a pointer to the new callback array + element. + c. cupsdDoSelect() uses epoll_wait() with the global event + buffer allocated in cupsdStartSelect() and then loops + through the events, using the user data field to find + the callback record. + d. cupsdStopSelect() closes the epoll file descriptor and + frees all of the memory used by the event buffer. + + 4. kqueue() + b. cupsdStartSelect() creates kqueue file descriptor + using kqyeue() function and allocates a global event + buffer. + c. cupsdAdd/RemoveSelect() uses EV_SET and kevent() to + register the changes. The event user data field is a + pointer to the new callback array element. + d. cupsdDoSelect() uses kevent() to poll for events and + loops through the events, using the user data field to + find the callback record. + e. cupsdStopSelect() closes the kqyeye() file descriptor + and frees all of the memory used by the event buffer. + + 5. /dev/poll + a. cupsdStartSelect() opens /dev/poll and allocates an + array of pollfd structs; on failure to open /dev/poll, + revert to poll() system call. + b. cupsdAddSelect() writes a single pollfd struct to + /dev/poll with the new file descriptor and the + POLLIN/POLLOUT flags. + c. cupsdRemoveSelect() writes a single pollfd struct to + /dev/poll with the file descriptor and the POLLREMOVE + flag. + d. cupsdDoSelect() uses the DP_POLL ioctl to retrieve + events from /dev/poll and then loops through the + returned pollfd array, looking up the file descriptors + as needed. + e. cupsdStopSelect() closes /dev/poll and frees the + pollfd array. + f. Need to benchmark to see if it is more efficient than + using poll() - this is the only mechanism that is O(n + log n), all of the others are O(n)... |