[pulseaudio-discuss] [PATCH 04/11] srchannel: Add the shared ringbuffer object
Peter Meerwald
pmeerw at pmeerw.net
Tue May 6 07:01:33 PDT 2014
Hello,
> An shm ringbuffer that is used for low overhead server-client communication.
> Signalling is done through eventfd semaphores - it's based on pa_fdsem to avoid
> syscalls if nothing is waiting on the other side.
comment inline
> ---
> src/Makefile.am | 3 +-
> src/pulsecore/srchannel.c | 297 ++++++++++++++++++++++++++++++++++++++++++++++
> src/pulsecore/srchannel.h | 62 ++++++++++
> 3 files changed, 361 insertions(+), 1 deletion(-)
> create mode 100644 src/pulsecore/srchannel.c
> create mode 100644 src/pulsecore/srchannel.h
>
> diff --git a/src/Makefile.am b/src/Makefile.am
> index 5c2d5bc..9e72982 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -618,6 +618,7 @@ libpulsecommon_ at PA_MAJORMINOR@_la_SOURCES = \
> pulsecore/creds.h \
> pulsecore/dynarray.c pulsecore/dynarray.h \
> pulsecore/endianmacros.h \
> + pulsecore/fdsem.c pulsecore/fdsem.h \
> pulsecore/flist.c pulsecore/flist.h \
> pulsecore/g711.c pulsecore/g711.h \
> pulsecore/hashmap.c pulsecore/hashmap.h \
> @@ -651,6 +652,7 @@ libpulsecommon_ at PA_MAJORMINOR@_la_SOURCES = \
> pulsecore/queue.c pulsecore/queue.h \
> pulsecore/random.c pulsecore/random.h \
> pulsecore/refcnt.h \
> + pulsecore/srchannel.c pulsecore/srchannel.h \
> pulsecore/sample-util.c pulsecore/sample-util.h \
> pulsecore/shm.c pulsecore/shm.h \
> pulsecore/bitset.c pulsecore/bitset.h \
> @@ -880,7 +882,6 @@ libpulsecore_ at PA_MAJORMINOR@_la_SOURCES = \
> pulsecore/core-scache.c pulsecore/core-scache.h \
> pulsecore/core-subscribe.c pulsecore/core-subscribe.h \
> pulsecore/core.c pulsecore/core.h \
> - pulsecore/fdsem.c pulsecore/fdsem.h \
> pulsecore/hook-list.c pulsecore/hook-list.h \
> pulsecore/ltdl-helper.c pulsecore/ltdl-helper.h \
> pulsecore/modargs.c pulsecore/modargs.h \
> diff --git a/src/pulsecore/srchannel.c b/src/pulsecore/srchannel.c
> new file mode 100644
> index 0000000..15485b2
> --- /dev/null
> +++ b/src/pulsecore/srchannel.c
> @@ -0,0 +1,297 @@
> +/***
> + This file is part of PulseAudio.
> +
> + Copyright 2014 David Henningsson, Canonical Ltd.
> +
> + 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
> + Lesser 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 "srchannel.h"
> +
> +#include <pulsecore/atomic.h>
> +#include <pulse/xmalloc.h>
> +
> +/* #define DEBUG_SRCHANNEL */
> +
> +/* This ringbuffer might be useful in other contexts too, but
> + right now it's only used inside the srchannel, so let's keep it here
> + for the time being. */
count is atomic, but readindex, writeindex are not
the assumption is that there is exactly one reader and
exactly one writer?
> +typedef struct pa_ringbuffer pa_ringbuffer;
> +struct pa_ringbuffer {
> + pa_atomic_t *count;
> + int capacity;
> + uint8_t *memory;
> + int readindex, writeindex;
> +};
> +
> +static void *pa_ringbuffer_peek(pa_ringbuffer *r, int *count) {
> + int c = pa_atomic_load(r->count);
> + if (r->readindex + c > r->capacity)
> + *count = r->capacity - r->readindex;
> + else
> + *count = c;
> + return r->memory + r->readindex;
> +}
> +
> +/* Returns true only if the buffer was completely full before the drop. */
> +static bool pa_ringbuffer_drop(pa_ringbuffer *r, int count) {
> + bool b = pa_atomic_sub(r->count, count) >= r->capacity;
> + r->readindex += count;
> + r->readindex %= r->capacity;
> + return b;
> +}
> +
> +static void *pa_ringbuffer_begin_write(pa_ringbuffer *r, int *count) {
> + int c = pa_atomic_load(r->count);
> + *count = PA_MIN(r->capacity - r->writeindex, r->capacity - c);
> + return r->memory + r->writeindex;
> +}
> +
> +static void pa_ringbuffer_end_write(pa_ringbuffer *r, int count) {
> + pa_atomic_add(r->count, count);
> + r->writeindex += count;
> + r->writeindex %= r->capacity;
> +}
> +
> +struct pa_srchannel {
> + pa_ringbuffer rb_read, rb_write;
> + pa_fdsem *sem_read, *sem_write;
> + pa_memblock *memblock;
> + void *cb_userdata;
> + pa_srchannel_cb_t callback;
> + pa_io_event *read_event;
> + pa_mainloop_api *mainloop;
> +};
> +
> +ssize_t pa_srchannel_write(pa_srchannel *sr, const void *data, size_t l) {
> + ssize_t written = 0;
> + while (l > 0) {
> + int towrite;
> + void *ptr = pa_ringbuffer_begin_write(&sr->rb_write, &towrite);
> + if ((size_t) towrite > l)
> + towrite = l;
> + if (towrite == 0) {
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("srchannel output buffer full");
> +#endif
> + break;
> + }
> + memcpy(ptr, data, towrite);
> + pa_ringbuffer_end_write(&sr->rb_write, towrite);
> + written += towrite;
> + data = (uint8_t*) data + towrite;
> + l -= towrite;
> + }
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Wrote %d bytes to srchannel, signalling fdsem", (int) written);
> +#endif
> + pa_fdsem_post(sr->sem_write);
> + return written;
> +}
> +
> +ssize_t pa_srchannel_read(pa_srchannel *sr, void *data, size_t l) {
> + ssize_t isread = 0;
> + while (l > 0) {
> + int toread;
> + void *ptr = pa_ringbuffer_peek(&sr->rb_read, &toread);
> + if ((size_t) toread > l)
> + toread = l;
> + if (toread == 0)
> + break;
> + memcpy(data, ptr, toread);
> + if (pa_ringbuffer_drop(&sr->rb_read, toread)) {
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("read from full output buffer, signalling fdsem");
> +#endif
> + pa_fdsem_post(sr->sem_write);
> + }
> +
> + isread += toread;
> + data = (uint8_t*) data + toread;
> + l -= toread;
> + }
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Read %d bytes from srchannel", (int) isread);
> +#endif
> + return isread;
> +}
> +
> +/* This is the memory layout of the ringbuffer shm block. It is followed by
> + read and write ringbuffer memory. */
> +struct srheader {
> + pa_atomic_t read_count;
> + pa_atomic_t write_count;
> + pa_fdsem_data read_semdata;
> + pa_fdsem_data write_semdata;
> + int capacity;
> + int readbuf_offset;
> + int writebuf_offset;
> + /* TODO: Maybe a marker here to make sure we talk to a server with equally sized struct */
> +};
> +
> +static void read_loop(pa_srchannel* sr) {
> + do {
> + int q;
> + pa_ringbuffer_peek(&sr->rb_read, &q);
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("In read loop from srchannel, before callback, count = %d", q);
> +#endif
> +
> + if (q > 0 && sr->callback)
> + if (!sr->callback(sr, sr->cb_userdata)) {
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Aborting read loop from srchannel");
> +#endif
> + return;
> + }
> +
> +#ifdef DEBUG_SRCHANNEL
> + pa_ringbuffer_peek(&sr->rb_read, &q);
> + pa_log("In read loop from srchannel, after callback, count = %d", q);
> +#endif
> +
> + } while (pa_fdsem_before_poll(sr->sem_read) < 0);
> +}
> +
> +static void read_cb(pa_mainloop_api *m, pa_io_event *e, int fd, pa_io_event_flags_t events, void *userdata) {
> + pa_srchannel* sr = userdata;
> +
> + pa_fdsem_after_poll(sr->sem_read);
> + read_loop(sr);
> +}
> +
> +pa_srchannel* pa_srchannel_new(pa_mainloop_api *m, pa_mempool *p) {
> + int capacity;
> + int readfd;
> + struct srheader *srh;
> +
> + pa_srchannel* sr = pa_xmalloc0(sizeof(pa_srchannel));
> + sr->mainloop = m;
> + sr->memblock = pa_memblock_new_pool(p, -1);
> + srh = pa_memblock_acquire(sr->memblock);
> + pa_zero(*srh);
> +
> + sr->rb_read.memory = (uint8_t*) srh + PA_ALIGN(sizeof(*srh));
> + srh->readbuf_offset = sr->rb_read.memory - (uint8_t*) srh;
> + capacity = (pa_memblock_get_length(sr->memblock) - srh->readbuf_offset) / 2;
> + sr->rb_write.memory = PA_ALIGN_PTR(sr->rb_read.memory + capacity);
> + srh->writebuf_offset = sr->rb_write.memory - (uint8_t*) srh;
> + capacity = PA_MIN(capacity, srh->writebuf_offset - srh->readbuf_offset);
> + pa_log_debug("SHM block is %d bytes, ringbuffer capacity is 2 * %d bytes",
> + (int) pa_memblock_get_length(sr->memblock), capacity);
> +
> + srh->capacity = sr->rb_read.capacity = sr->rb_write.capacity = capacity;
> + sr->rb_read.count = &srh->read_count;
> + sr->rb_write.count = &srh->write_count;
> +
> + sr->sem_read = pa_fdsem_new_shm(&srh->read_semdata);
> + sr->sem_write = pa_fdsem_new_shm(&srh->write_semdata);
> +
> + readfd = pa_fdsem_get(sr->sem_read);
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Enabling io event on fd %d", readfd);
> +#endif
> + sr->read_event = m->io_new(m, readfd, PA_IO_EVENT_INPUT, read_cb, sr);
> + m->io_enable(sr->read_event, PA_IO_EVENT_INPUT);
> +
> + return sr;
> +}
> +
> +static void pa_srchannel_swap(pa_srchannel *sr) {
> + pa_srchannel temp = *sr;
> + sr->sem_read = temp.sem_write;
> + sr->sem_write = temp.sem_read;
> + sr->rb_read = temp.rb_write;
> + sr->rb_write = temp.rb_read;
> +}
> +
> +pa_srchannel* pa_srchannel_new_from_template(pa_mainloop_api *m, pa_srchannel_template *t)
> +{
> + int temp;
> + struct srheader *srh;
> + pa_srchannel* sr = pa_xmalloc0(sizeof(pa_srchannel));
> +
> + sr->mainloop = m;
> + sr->memblock = t->memblock;
> + pa_memblock_ref(sr->memblock);
> + srh = pa_memblock_acquire(sr->memblock);
> +
> + sr->rb_read.capacity = sr->rb_write.capacity = srh->capacity;
> + sr->rb_read.count = &srh->read_count;
> + sr->rb_write.count = &srh->write_count;
> + sr->rb_read.memory = (uint8_t*) srh + srh->readbuf_offset;
> + sr->rb_write.memory = (uint8_t*) srh + srh->writebuf_offset;
> +
> + sr->sem_read = pa_fdsem_open_shm(&srh->read_semdata, t->readfd);
> + sr->sem_write = pa_fdsem_open_shm(&srh->write_semdata, t->writefd);
> +
> + pa_srchannel_swap(sr);
> + temp = t->readfd; t->readfd = t->writefd; t->writefd = temp;
> +
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Enabling io event on fd %d", t->readfd);
> +#endif
> + sr->read_event = m->io_new(m, t->readfd, PA_IO_EVENT_INPUT, read_cb, sr);
> + m->io_enable(sr->read_event, PA_IO_EVENT_INPUT);
> +
> + return sr;
> +}
> +
> +void pa_srchannel_export(pa_srchannel *sr, pa_srchannel_template *t) {
> + t->memblock = sr->memblock;
> + t->readfd = pa_fdsem_get(sr->sem_read);
> + t->writefd = pa_fdsem_get(sr->sem_write);
> +}
> +
> +void pa_srchannel_set_callback(pa_srchannel *sr, pa_srchannel_cb_t callback, void *userdata) {
> + if (sr->callback)
> + pa_fdsem_after_poll(sr->sem_read);
> +
> + sr->callback = callback;
> + sr->cb_userdata = userdata;
> +
> + if (sr->callback)
> + /* Maybe deferred event? */
> + read_loop(sr);
> +}
> +
> +void pa_srchannel_free(pa_srchannel *sr)
> +{
> +#ifdef DEBUG_SRCHANNEL
> + pa_log("Freeing srchannel");
> +#endif
> + if (!sr)
> + return;
> +
> + if (sr->read_event)
> + sr->mainloop->io_free(sr->read_event);
> +
> + if (sr->sem_read)
> + pa_fdsem_free(sr->sem_read);
> + if (sr->sem_write)
> + pa_fdsem_free(sr->sem_write);
> +
> + if (sr->memblock) {
> + pa_memblock_release(sr->memblock);
> + pa_memblock_unref(sr->memblock);
> + }
> +
> + pa_xfree(sr);
> +}
> diff --git a/src/pulsecore/srchannel.h b/src/pulsecore/srchannel.h
> new file mode 100644
> index 0000000..8eac77f
> --- /dev/null
> +++ b/src/pulsecore/srchannel.h
> @@ -0,0 +1,62 @@
> +#ifndef foopulsesrchannelhfoo
> +#define foopulsesrchannelhfoo
> +
> +/***
> + This file is part of PulseAudio.
> +
> + Copyright 2014 David Henningsson, Canonical Ltd.
> +
> + 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
> + Lesser 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.
> +***/
> +
> +#include <pulse/mainloop-api.h>
> +#include <pulsecore/fdsem.h>
> +#include <pulsecore/memblock.h>
> +
> +/* An shm ringbuffer that is used for low overhead server-client communication.
> + Signaling is done through eventfd semaphores (pa_fdsem). */
> +
> +typedef struct pa_srchannel pa_srchannel;
> +
> +typedef struct pa_srchannel_template {
> + int readfd, writefd;
> + pa_memblock *memblock;
> +} pa_srchannel_template;
> +
> +pa_srchannel* pa_srchannel_new(pa_mainloop_api *m, pa_mempool *p);
> +/* Note: this creates a srchannel with swapped read and write. */
> +pa_srchannel* pa_srchannel_new_from_template(pa_mainloop_api *m, pa_srchannel_template *t);
> +
> +void pa_srchannel_free(pa_srchannel *sr);
> +
> +void pa_srchannel_export(pa_srchannel *sr, pa_srchannel_template *t);
> +
> +ssize_t pa_srchannel_write(pa_srchannel *sr, const void *data, size_t l);
> +ssize_t pa_srchannel_read(pa_srchannel *sr, void *data, size_t l);
> +
> +/* Set the callback function that is called whenever data becomes available for reading.
> + It can also be called if the output buffer was full and can now be written to.
> +
> + Return false to abort all processing (e g if the srchannel has been freed during the callback).
> + Otherwise return true.
> +
> + Note that if the ringbuffer is not empty when the callback is set up, the callback
> + will be called immediately.
> +*/
> +typedef bool (*pa_srchannel_cb_t)(pa_srchannel *sr, void *userdata);
> +void pa_srchannel_set_callback(pa_srchannel *sr, pa_srchannel_cb_t callback, void *userdata);
> +
> +#endif
>
--
Peter Meerwald
+43-664-2444418 (mobile)
More information about the pulseaudio-discuss
mailing list