diff options
author | Lennart Poettering <lennart@poettering.net> | 2009-04-22 19:10:09 +0200 |
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committer | Lennart Poettering <lennart@poettering.net> | 2009-04-22 19:10:09 +0200 |
commit | ad12d7d4b020e6be225a8d6494de69d051ec7f81 (patch) | |
tree | fabaa0fd297f34891f7afd7663a7f9c28352f6bf /src/pulsecore | |
parent | bb07c16b63339c934097b6a631fee36d92285511 (diff) |
memtrap,aupdate: split atomic update from memtrap into seperate aupdate framework
Diffstat (limited to 'src/pulsecore')
-rw-r--r-- | src/pulsecore/aupdate.c | 129 | ||||
-rw-r--r-- | src/pulsecore/aupdate.h | 98 | ||||
-rw-r--r-- | src/pulsecore/memtrap.c | 116 | ||||
-rw-r--r-- | src/pulsecore/memtrap.h | 2 |
4 files changed, 263 insertions, 82 deletions
diff --git a/src/pulsecore/aupdate.c b/src/pulsecore/aupdate.c new file mode 100644 index 00000000..56ebb8e5 --- /dev/null +++ b/src/pulsecore/aupdate.c @@ -0,0 +1,129 @@ +/*** + This file is part of PulseAudio. + + Copyright 2009 Lennart Poettering + + PulseAudio is free software; you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + PulseAudio is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with PulseAudio; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 + USA. +***/ + +#ifdef HAVE_CONFIG_H +#include <config.h> +#endif + +#include <pulse/xmalloc.h> + +#include <pulsecore/semaphore.h> +#include <pulsecore/macro.h> +#include <pulsecore/mutex.h> + +#include "aupdate.h" + +#define MSB (1U << (sizeof(unsigned)*8U-1)) +#define WHICH(n) (!!((n) & MSB)) +#define COUNTER(n) ((n) & ~MSB) + +struct pa_aupdate { + pa_atomic_t read_lock; + pa_mutex *write_lock; + pa_semaphore *semaphore; +}; + +pa_aupdate *pa_aupdate_new(void) { + pa_aupdate *a; + + a = pa_xnew(pa_aupdate, 1); + pa_atomic_store(&a->read_lock, 0); + a->write_lock = pa_mutex_new(FALSE, FALSE); + a->semaphore = pa_semaphore_new(0); + + return a; +} + +void pa_aupdate_free(pa_aupdate *a) { + pa_assert(a); + + pa_mutex_free(a->write_lock); + pa_semaphore_free(a->semaphore); + + pa_xfree(a); +} + +unsigned pa_aupdate_read_begin(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + /* Increase the lock counter */ + n = (unsigned) pa_atomic_inc(&a->read_lock); + + /* When n is 0 we have about 2^31 threads running that all try to + * access the data at the same time, oh my! */ + pa_assert(COUNTER(n)+1 > 0); + + /* The uppermost bit tells us which data to look at */ + return WHICH(n); +} + +void pa_aupdate_read_end(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + /* Decrease the lock counter */ + n = (unsigned) pa_atomic_dec(&a->read_lock); + + /* Make sure the counter was valid */ + pa_assert(COUNTER(n) > 0); + + /* Post the semaphore */ + pa_semaphore_post(a->semaphore); +} + +unsigned pa_aupdate_write_begin(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + pa_mutex_lock(a->write_lock); + + n = (unsigned) pa_atomic_load(&a->read_lock); + + return !WHICH(n); +} + +unsigned pa_aupdate_write_swap(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + for (;;) { + n = (unsigned) pa_atomic_load(&a->read_lock); + + /* If the read counter is > 0 wait; if it is 0 try to swap the lists */ + if (COUNTER(n) > 0) + pa_semaphore_wait(a->semaphore); + else if (pa_atomic_cmpxchg(&a->read_lock, (int) n, (int) (n ^ MSB))) + break; + } + + return WHICH(n); +} + +void pa_aupdate_write_end(pa_aupdate *a) { + pa_assert(a); + + pa_mutex_unlock(a->write_lock); +} diff --git a/src/pulsecore/aupdate.h b/src/pulsecore/aupdate.h new file mode 100644 index 00000000..072e382d --- /dev/null +++ b/src/pulsecore/aupdate.h @@ -0,0 +1,98 @@ +#ifndef foopulsecoreaupdatehfoo +#define foopulsecoreaupdatehfoo + +/*** + This file is part of PulseAudio. + + Copyright 2009 Lennart Poettering + + PulseAudio is free software; you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + PulseAudio is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with PulseAudio; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 + USA. +***/ + +typedef struct pa_aupdate pa_aupdate; + +pa_aupdate *pa_aupdate_new(void); +void pa_aupdate_free(pa_aupdate *a); + +/* Will return 0, or 1, depending on which copy of the data the caller + * should look at */ +unsigned pa_aupdate_read_begin(pa_aupdate *a); +void pa_aupdate_read_end(pa_aupdate *a); + +/* Will return 0, or 1, depending which copy of the data the caller + * should modify */ +unsigned pa_aupdate_write_begin(pa_aupdate *a); +void pa_aupdate_write_end(pa_aupdate *a); + +/* Will return 0, or 1, depending which copy of the data the caller + * should modify. Each time called this will return the opposite of + * the previous pa_aupdate_write_begin()/pa_aupdate_write_swap() + * call. Should only be called between pa_aupdate_write_begin() and + * pa_aupdate_write_end() */ +unsigned pa_aupdate_write_swap(pa_aupdate *a); + +/* + * This infrastructure allows lock-free updates of arbitrary data + * structures in an rcu'ish way: two copies of the data structure + * should be exisiting. One side ('the reader') has read access to one + * of the two data structure at a time. It does not have to lock it, + * however it needs to signal that it is using it/stopped using + * it. The other side ('the writer') modifes the second data structure, + * and then atomically swaps the two data structures, followed by a + * modification of the other one. + * + * This is intended to be used for cases where the reader side needs + * to be fast while the writer side can be slow. + * + * The reader side is signal handler safe. + * + * The writer side lock is not recursive. The reader side is. + * + * There may be multiple readers and multiple writers at the same + * time. + * + * Usage is like this: + * + * static struct foo bar[2]; + * static pa_aupdate *a; + * + * reader() { + * unsigned j; + * + * j = pa_update_read_begin(a); + * + * ... read the data structure bar[j] ... + * + * pa_update_read_end(a); + * } + * + * writer() { + * unsigned j; + * + * j = pa_update_write_begin(a); + * + * ... update the data structure bar[j] ... + * + * j = pa_update_write_swap(a); + * + * ... update the data structure bar[j], the same way as above ... + * + * pa_update_write_end(a) + * } + * + */ + +#endif diff --git a/src/pulsecore/memtrap.c b/src/pulsecore/memtrap.c index e04e838e..bd0243e0 100644 --- a/src/pulsecore/memtrap.c +++ b/src/pulsecore/memtrap.c @@ -28,10 +28,10 @@ #include <pulse/xmalloc.h> -#include <pulsecore/semaphore.h> -#include <pulsecore/macro.h> -#include <pulsecore/mutex.h> #include <pulsecore/core-util.h> +#include <pulsecore/aupdate.h> +#include <pulsecore/atomic.h> +#include <pulsecore/once.h> #include "memtrap.h" @@ -43,13 +43,13 @@ struct pa_memtrap { }; static pa_memtrap *memtraps[2] = { NULL, NULL }; -static pa_atomic_t read_lock = PA_ATOMIC_INIT(0); -static pa_static_semaphore semaphore = PA_STATIC_SEMAPHORE_INIT; -static pa_static_mutex write_lock = PA_STATIC_MUTEX_INIT; +static pa_aupdate *aupdate; -#define MSB (1U << (sizeof(unsigned)*8U-1)) -#define WHICH(n) (!!((n) & MSB)) -#define COUNTER(n) ((n) & ~MSB) +static void allocate_aupdate(void) { + PA_ONCE_BEGIN { + aupdate = pa_aupdate_new(); + } PA_ONCE_END; +} pa_bool_t pa_memtrap_is_good(pa_memtrap *m) { pa_assert(m); @@ -62,19 +62,11 @@ static void sigsafe_error(const char *s) { } static void signal_handler(int sig, siginfo_t* si, void *data) { - unsigned n, j; + unsigned j; pa_memtrap *m; void *r; - /* Increase the lock counter */ - n = (unsigned) pa_atomic_inc(&read_lock); - - /* The uppermost bit tells us which list to look at */ - j = WHICH(n); - - /* When n is 0 we have about 2^31 threads running that - * all got a sigbus at the same time, oh my! */ - pa_assert(COUNTER(n)+1 > 0); + j = pa_aupdate_read_begin(aupdate); for (m = memtraps[j]; m; m = m->next[j]) if (si->si_addr >= m->start && @@ -94,33 +86,16 @@ static void signal_handler(int sig, siginfo_t* si, void *data) { pa_assert(r == m->start); - pa_atomic_dec(&read_lock); - - /* Post the semaphore */ - pa_semaphore_post(pa_static_semaphore_get(&semaphore, 0)); - + pa_aupdate_read_end(aupdate); return; fail: + pa_aupdate_read_end(aupdate); + sigsafe_error("Failed to handle SIGBUS.\n"); - pa_atomic_dec(&read_lock); abort(); } -static void memtrap_swap(unsigned n) { - - for (;;) { - - /* If the read counter is > 0 wait; if it is 0 try to swap the lists */ - if (COUNTER(n) > 0) - pa_semaphore_wait(pa_static_semaphore_get(&semaphore, 0)); - else if (pa_atomic_cmpxchg(&read_lock, (int) n, (int) (n ^ MSB))) - break; - - n = (unsigned) pa_atomic_load(&read_lock); - } -} - static void memtrap_link(pa_memtrap *m, unsigned j) { pa_assert(m); @@ -143,58 +118,47 @@ static void memtrap_unlink(pa_memtrap *m, unsigned j) { pa_memtrap* pa_memtrap_add(const void *start, size_t size) { pa_memtrap *m = NULL; - pa_mutex *lock; - unsigned n, j; + unsigned j; pa_assert(start); pa_assert(size > 0); pa_assert(PA_PAGE_ALIGN_PTR(start) == start); pa_assert(PA_PAGE_ALIGN(size) == size); - lock = pa_static_mutex_get(&write_lock, FALSE, FALSE); - pa_mutex_lock(lock); - - n = (unsigned) pa_atomic_load(&read_lock); - j = WHICH(n); - m = pa_xnew(pa_memtrap, 1); m->start = (void*) start; m->size = size; pa_atomic_store(&m->bad, 0); - memtrap_link(m, !j); - memtrap_swap(n); - memtrap_link(m, j); + allocate_aupdate(); - pa_mutex_unlock(lock); + j = pa_aupdate_write_begin(aupdate); + memtrap_link(m, j); + j = pa_aupdate_write_swap(aupdate); + memtrap_link(m, j); + pa_aupdate_write_end(aupdate); return m; } void pa_memtrap_remove(pa_memtrap *m) { - unsigned n, j; - pa_mutex *lock; + unsigned j; pa_assert(m); - lock = pa_static_mutex_get(&write_lock, FALSE, FALSE); - pa_mutex_lock(lock); + allocate_aupdate(); - n = (unsigned) pa_atomic_load(&read_lock); - j = WHICH(n); - - memtrap_unlink(m, !j); - memtrap_swap(n); + j = pa_aupdate_write_begin(aupdate); + memtrap_unlink(m, j); + j = pa_aupdate_write_swap(aupdate); memtrap_unlink(m, j); + pa_aupdate_write_end(aupdate); pa_xfree(m); - - pa_mutex_unlock(lock); } pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size) { - unsigned n, j; - pa_mutex *lock; + unsigned j; pa_assert(m); @@ -203,32 +167,25 @@ pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size) { pa_assert(PA_PAGE_ALIGN_PTR(start) == start); pa_assert(PA_PAGE_ALIGN(size) == size); - lock = pa_static_mutex_get(&write_lock, FALSE, FALSE); - pa_mutex_lock(lock); + allocate_aupdate(); + + j = pa_aupdate_write_begin(aupdate); if (m->start == start && m->size == size) goto unlock; - n = (unsigned) pa_atomic_load(&read_lock); - j = WHICH(n); - - memtrap_unlink(m, !j); - memtrap_swap(n); memtrap_unlink(m, j); + j = pa_aupdate_write_swap(aupdate); m->start = (void*) start; m->size = size; pa_atomic_store(&m->bad, 0); - n = (unsigned) pa_atomic_load(&read_lock); - j = WHICH(n); - - memtrap_link(m, !j); - memtrap_swap(n); + j = pa_aupdate_write_swap(aupdate); memtrap_link(m, j); unlock: - pa_mutex_unlock(lock); + pa_aupdate_write_end(aupdate); return m; } @@ -236,10 +193,7 @@ unlock: void pa_memtrap_install(void) { struct sigaction sa; - /* Before we install the signal handler, make sure the semaphore - * is valid so that the initialization of the semaphore - * doesn't have to happen from the signal handler */ - pa_static_semaphore_get(&semaphore, 0); + allocate_aupdate(); memset(&sa, 0, sizeof(sa)); sa.sa_sigaction = signal_handler; diff --git a/src/pulsecore/memtrap.h b/src/pulsecore/memtrap.h index f7da7083..fa38da58 100644 --- a/src/pulsecore/memtrap.h +++ b/src/pulsecore/memtrap.h @@ -34,7 +34,7 @@ * still 'good' i.e. no SIGBUS has happened yet for it. * * Intended usage is to handle memory mapped in which is controlled by - * other processes that might execute ftruncate() or when mapping in + * other processes that might execute ftruncate() or when mapping inb * hardware resources that might get invalidated when unplugged. */ typedef struct pa_memtrap pa_memtrap; |