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4 Commits
| Author | SHA1 | Message | Date | |
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Joseph Myers
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688903eb3e |
Update copyright dates with scripts/update-copyrights.
* All files with FSF copyright notices: Update copyright dates using scripts/update-copyrights. * locale/programs/charmap-kw.h: Regenerated. * locale/programs/locfile-kw.h: Likewise. |
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Joseph Myers
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bfff8b1bec | Update copyright dates with scripts/update-copyrights. | ||
Torvald Riegel
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ed19993b5b |
New condvar implementation that provides stronger ordering guarantees.
This is a new implementation for condition variables, required after http://austingroupbugs.net/view.php?id=609 to fix bug 13165. In essence, we need to be stricter in which waiters a signal or broadcast is required to wake up; this couldn't be solved using the old algorithm. ISO C++ made a similar clarification, so this also fixes a bug in current libstdc++, for example. We can't use the old algorithm anymore because futexes do not guarantee to wake in FIFO order. Thus, when we wake, we can't simply let any waiter grab a signal, but we need to ensure that one of the waiters happening before the signal is woken up. This is something the previous algorithm violated (see bug 13165). There's another issue specific to condvars: ABA issues on the underlying futexes. Unlike mutexes that have just three states, or semaphores that have no tokens or a limited number of them, the state of a condvar is the *order* of the waiters. A waiter on a semaphore can grab a token whenever one is available; a condvar waiter must only consume a signal if it is eligible to do so as determined by the relative order of the waiter and the signal. Therefore, this new algorithm maintains two groups of waiters: Those eligible to consume signals (G1), and those that have to wait until previous waiters have consumed signals (G2). Once G1 is empty, G2 becomes the new G1. 64b counters are used to avoid ABA issues. This condvar doesn't yet use a requeue optimization (ie, on a broadcast, waking just one thread and requeueing all others on the futex of the mutex supplied by the program). I don't think doing the requeue is necessarily the right approach (but I haven't done real measurements yet): * If a program expects to wake many threads at the same time and make that scalable, a condvar isn't great anyway because of how it requires waiters to operate mutually exclusive (due to the mutex usage). Thus, a thundering herd problem is a scalability problem with or without the optimization. Using something like a semaphore might be more appropriate in such a case. * The scalability problem is actually at the mutex side; the condvar could help (and it tries to with the requeue optimization), but it should be the mutex who decides how that is done, and whether it is done at all. * Forcing all but one waiter into the kernel-side wait queue of the mutex prevents/avoids the use of lock elision on the mutex. Thus, it prevents the only cure against the underlying scalability problem inherent to condvars. * If condvars use short critical sections (ie, hold the mutex just to check a binary flag or such), which they should do ideally, then forcing all those waiter to proceed serially with kernel-based hand-off (ie, futex ops in the mutex' contended state, via the futex wait queues) will be less efficient than just letting a scalable mutex implementation take care of it. Our current mutex impl doesn't employ spinning at all, but if critical sections are short, spinning can be much better. * Doing the requeue stuff requires all waiters to always drive the mutex into the contended state. This leads to each waiter having to call futex_wake after lock release, even if this wouldn't be necessary. [BZ #13165] * nptl/pthread_cond_broadcast.c (__pthread_cond_broadcast): Rewrite to use new algorithm. * nptl/pthread_cond_destroy.c (__pthread_cond_destroy): Likewise. * nptl/pthread_cond_init.c (__pthread_cond_init): Likewise. * nptl/pthread_cond_signal.c (__pthread_cond_signal): Likewise. * nptl/pthread_cond_wait.c (__pthread_cond_wait): Likewise. (__pthread_cond_timedwait): Move here from pthread_cond_timedwait.c. (__condvar_confirm_wakeup, __condvar_cancel_waiting, __condvar_cleanup_waiting, __condvar_dec_grefs, __pthread_cond_wait_common): New. (__condvar_cleanup): Remove. * npt/pthread_condattr_getclock.c (pthread_condattr_getclock): Adapt. * npt/pthread_condattr_setclock.c (pthread_condattr_setclock): Likewise. * npt/pthread_condattr_getpshared.c (pthread_condattr_getpshared): Likewise. * npt/pthread_condattr_init.c (pthread_condattr_init): Likewise. * nptl/tst-cond1.c: Add comment. * nptl/tst-cond20.c (do_test): Adapt. * nptl/tst-cond22.c (do_test): Likewise. * sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_cond_t): Adapt structure. * sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/x86/bits/pthreadtypes.h (pthread_cond_t): Likewise. * sysdeps/nptl/internaltypes.h (COND_NWAITERS_SHIFT): Remove. (COND_CLOCK_BITS): Adapt. * sysdeps/nptl/pthread.h (PTHREAD_COND_INITIALIZER): Adapt. * nptl/pthreadP.h (__PTHREAD_COND_CLOCK_MONOTONIC_MASK, __PTHREAD_COND_SHARED_MASK): New. * nptl/nptl-printers.py (CLOCK_IDS): Remove. (ConditionVariablePrinter, ConditionVariableAttributesPrinter): Adapt. * nptl/nptl_lock_constants.pysym: Adapt. * nptl/test-cond-printers.py: Adapt. * sysdeps/unix/sysv/linux/hppa/internaltypes.h (cond_compat_clear, cond_compat_check_and_clear): Adapt. * sysdeps/unix/sysv/linux/hppa/pthread_cond_timedwait.c: Remove file ... * sysdeps/unix/sysv/linux/hppa/pthread_cond_wait.c (__pthread_cond_timedwait): ... and move here. * nptl/DESIGN-condvar.txt: Remove file. * nptl/lowlevelcond.sym: Likewise. * nptl/pthread_cond_timedwait.c: Likewise. * sysdeps/unix/sysv/linux/i386/i486/pthread_cond_broadcast.S: Likewise. * sysdeps/unix/sysv/linux/i386/i486/pthread_cond_signal.S: Likewise. * sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S: Likewise. * sysdeps/unix/sysv/linux/i386/i486/pthread_cond_wait.S: Likewise. * sysdeps/unix/sysv/linux/i386/i586/pthread_cond_broadcast.S: Likewise. * sysdeps/unix/sysv/linux/i386/i586/pthread_cond_signal.S: Likewise. * sysdeps/unix/sysv/linux/i386/i586/pthread_cond_timedwait.S: Likewise. * sysdeps/unix/sysv/linux/i386/i586/pthread_cond_wait.S: Likewise. * sysdeps/unix/sysv/linux/i386/i686/pthread_cond_broadcast.S: Likewise. * sysdeps/unix/sysv/linux/i386/i686/pthread_cond_signal.S: Likewise. * sysdeps/unix/sysv/linux/i386/i686/pthread_cond_timedwait.S: Likewise. * sysdeps/unix/sysv/linux/i386/i686/pthread_cond_wait.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/pthread_cond_broadcast.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/pthread_cond_signal.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S: Likewise. * sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S: Likewise. |
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Martin Galvan
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23b5cae1af |
Add pretty printers for the NPTL lock types
This patch adds pretty printers for the following NPTL types: - pthread_mutex_t - pthread_mutexattr_t - pthread_cond_t - pthread_condattr_t - pthread_rwlock_t - pthread_rwlockattr_t To load the pretty printers into your gdb session, do the following: python import sys sys.path.insert(0, '/path/to/glibc/build/nptl/pretty-printers') end source /path/to/glibc/source/pretty-printers/nptl-printers.py You can check which printers are registered and enabled by issuing the 'info pretty-printer' gdb command. Printers should trigger automatically when trying to print a variable of one of the types mentioned above. The printers are architecture-independent, and were tested on an AMD64 running Ubuntu 14.04 and an x86 VM running Fedora 24. In order to work, the printers need to know the values of various flags that are scattered throughout pthread.h and pthreadP.h as enums and #defines. Since replicating these constants in the printers file itself would create a maintenance burden, I wrote a script called gen-py-const.awk that Makerules uses to extract the constants. This script is pretty much the same as gen-as-const.awk, except it doesn't cast the constant values to 'long' and is thorougly documented. The constants need only to be enumerated in a .pysym file, which is then referenced by a Make variable called gen-py-const-headers. As for the install directory, I discussed this with Mike Frysinger and Siddhesh Poyarekar, and we agreed that it can be handled in a separate patch, and shouldn't block merging of this one. In addition, I've written a series of test cases for the pretty printers. Each lock type (mutex, condvar and rwlock) has two test programs, one for itself and other for its related 'attributes' object. Each test program in turn has a PExpect-based Python script that drives gdb and compares its output to the expected printer's. The tests run on the glibc host, which is assumed to have both gdb and PExpect; if either is absent the tests will fail with code 77 (UNSUPPORTED). For cross-testing you should use cross-test-ssh.sh as test-wrapper. I've tested the printers on both native builds and a cross build using a Beaglebone Black running Debian, with the build system's filesystem shared with the board through NFS. Finally, I've written a README that explains all this and more. * INSTALL: Regenerated. * Makeconfig: Add comments and whitespace to make the control flow clearer. (+link-printers-tests, +link-pie-printers-tests, CFLAGS-printers-tests, installed-rtld-LDFLAGS, built-rtld-LDFLAGS, link-libc-rpath, link-libc-tests-after-rpath-link, link-libc-printers-tests): New. (rtld-LDFLAGS, rtld-tests-LDFLAGS, link-libc-tests-rpath-link, link-libc-tests): Use the new variables as required. * Makerules ($(py-const)): New rule. generated: Add $(py-const). * README.pretty-printers: New file. * Rules (tests-printers-programs, tests-printers-out, py-env): New. (others): Depend on $(py-const). (tests): Depend on $(tests-printers-programs) or $(tests-printers-out), as required. Pass $(tests-printers) to merge-test-results.sh. * manual/install.texi: Add requirements for testing the pretty printers. * nptl/Makefile (gen-py-const-headers, pretty-printers, tests-printers, CFLAGS-test-mutexattr-printers.c CFLAGS-test-mutex-printers.c, CFLAGS-test-condattr-printers.c, CFLAGS-test-cond-printers.c, CFLAGS-test-rwlockattr-printers.c CFLAGS-test-rwlock-printers.c, tests-printers-libs): Define. * nptl/nptl-printers.py: New file. * nptl/nptl_lock_constants.pysym: Likewise. * nptl/test-cond-printers.c: Likewise. * nptl/test-cond-printers.py: Likewise. * nptl/test-condattr-printers.c: Likewise. * nptl/test-condattr-printers.py: Likewise. * nptl/test-mutex-printers.c: Likewise. * nptl/test-mutex-printers.py: Likewise. * nptl/test-mutexattr-printers.c: Likewise. * nptl/test-mutexattr-printers.py: Likewise. * nptl/test-rwlock-printers.c: Likewise. * nptl/test-rwlock-printers.py: Likewise. * nptl/test-rwlockattr-printers.c: Likewise. * nptl/test-rwlockattr-printers.py: Likewise. * scripts/gen-py-const.awk: Likewise. * scripts/test_printers_common.py: Likewise. * scripts/test_printers_exceptions.py: Likewise. |