Mercurial > hg > octave-lojdl > gnulib-hg
changeset 16869:38e6d30d7e4d
poll/select: prevent busy-waiting
2012-05-21 Paolo Bonzini <bonzini@gnu.org>
poll/select: prevent busy-waiting. SwitchToThread() only gives away
the rest of the current time slice to another thread in the current
process. So if the thread that feeds the file decscriptor we're
polling is not in the current process, we get busy-waiting.
* lib/poll.c: Use SleepEx(1, TRUE) instead of SwitchToThread().
Patch from Theodore Leblond.
* lib/select.c: Split polling out of the loop that sets the output
fd_sets. Check for zero result and loop if the wait timeout is
infinite.
author | Paolo Bonzini <bonzini@gnu.org> |
---|---|
date | Mon, 21 May 2012 09:52:42 +0200 |
parents | 1def4f23c989 |
children | eabd04107c92 |
files | ChangeLog lib/poll.c lib/select.c |
diffstat | 3 files changed, 55 insertions(+), 19 deletions(-) [+] |
line wrap: on
line diff
--- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,15 @@ +2012-05-21 Paolo Bonzini <bonzini@gnu.org> + + poll/select: prevent busy-waiting. SwitchToThread() only gives away + the rest of the current time slice to another thread in the current + process. So if the thread that feeds the file decscriptor we're + polling is not in the current process, we get busy-waiting. + * lib/poll.c: Use SleepEx(1, TRUE) instead of SwitchToThread(). + Patch from Theodore Leblond. + * lib/select.c: Split polling out of the loop that sets the output + fd_sets. Check for zero result and loop if the wait timeout is + infinite. + 2012-05-21 Eric Blake <eblake@redhat.com> strdup: undeprecate, IRIX 6.5 needs it
--- a/lib/poll.c +++ b/lib/poll.c @@ -598,7 +598,7 @@ if (!rc && timeout == INFTIM) { - SwitchToThread(); + SleepEx (1, TRUE); goto restart; }
--- a/lib/select.c +++ b/lib/select.c @@ -385,6 +385,10 @@ } } + /* Place a sentinel at the end of the array. */ + handle_array[nhandles] = NULL; + +restart: if (wait_timeout == 0 || nsock == 0) rc = 0; else @@ -427,13 +431,44 @@ if (rc == 0 && nsock > 0) rc = select (0, &handle_rfds, &handle_wfds, &handle_xfds, &tv0); + if (nhandles > 1) + { + /* Count results that are not counted in the return value of select. */ + nhandles = 1; + for (i = 0; i < nfds; i++) + { + if ((anyfds_in[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) == 0) + continue; + + h = (HANDLE) _get_osfhandle (i); + if (h == handle_array[nhandles]) + { + /* Not a socket. */ + nhandles++; + windows_poll_handle (h, i, &rbits, &wbits, &xbits); + if (rbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))) + || wbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1))) + || xbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) + rc++; + } + } + + if (rc == 0 && wait_timeout == INFINITE) + { + /* Sleep 1 millisecond to avoid busy wait and retry with the + original fd_sets. */ + memcpy (&handle_rfds, rfds, sizeof (fd_set)); + memcpy (&handle_wfds, wfds, sizeof (fd_set)); + memcpy (&handle_xfds, xfds, sizeof (fd_set)); + SleepEx (1, TRUE); + goto restart; + } + } + /* Now fill in the results. */ FD_ZERO (rfds); FD_ZERO (wfds); FD_ZERO (xfds); - - /* Place a sentinel at the end of the array. */ - handle_array[nhandles] = NULL; nhandles = 1; for (i = 0; i < nfds; i++) { @@ -443,8 +478,7 @@ h = (HANDLE) _get_osfhandle (i); if (h != handle_array[nhandles]) { - /* Perform handle->descriptor mapping. Don't update rc, as these - results are counted in the return value of Winsock's select. */ + /* Perform handle->descriptor mapping. */ WSAEventSelect ((SOCKET) h, NULL, 0); if (FD_ISSET (h, &handle_rfds)) FD_SET (i, rfds); @@ -457,22 +491,12 @@ { /* Not a socket. */ nhandles++; - windows_poll_handle (h, i, &rbits, &wbits, &xbits); if (rbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) - { - rc++; - FD_SET (i, rfds); - } + FD_SET (i, rfds); if (wbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) - { - rc++; - FD_SET (i, wfds); - } + FD_SET (i, wfds); if (xbits.out[i / CHAR_BIT] & (1 << (i & (CHAR_BIT - 1)))) - { - rc++; - FD_SET (i, xfds); - } + FD_SET (i, xfds); } }