static STATUS xsem_take(struct wind_sem *sem, int timeout)
{
struct timespec ts, *timespec;
struct syncstate syns;
struct service svc;
STATUS ret = OK;
if (threadobj_irq_p())
return S_intLib_NOT_ISR_CALLABLE;
CANCEL_DEFER(svc);
if (syncobj_lock(&sem->u.xsem.sobj, &syns)) {
ret = S_objLib_OBJ_ID_ERROR;
goto out;
}
if (--sem->u.xsem.value >= 0)
goto done;
if (timeout == NO_WAIT) {
sem->u.xsem.value++;
ret = S_objLib_OBJ_UNAVAILABLE;
goto done;
}
if (timeout != WAIT_FOREVER) {
timespec = &ts;
clockobj_ticks_to_timeout(&wind_clock, timeout, timespec);
} else
timespec = NULL;
ret = syncobj_wait_grant(&sem->u.xsem.sobj, timespec, &syns);
if (ret == -EIDRM) {
ret = S_objLib_OBJ_DELETED;
goto out;
}
if (ret) {
sem->u.xsem.value++;
if (ret == -ETIMEDOUT)
ret = S_objLib_OBJ_TIMEOUT;
else if (ret == -EINTR)
ret = OK; /* Flushed. */
}
done:
syncobj_unlock(&sem->u.xsem.sobj, &syns);
out:
CANCEL_RESTORE(svc);
return ret;
}
/**
* @fn ssize_t rt_buffer_read_timed(RT_BUFFER *bf, void *ptr, size_t len, const struct timespec *abs_timeout)
* @brief Read from an IPC buffer.
*
* This routine reads the next message from the specified buffer. If
* no message is available on entry, the caller is allowed to block
* until enough data is written to the buffer, or a timeout elapses.
*
* @param bf The descriptor address of the buffer to read from.
*
* @param ptr A pointer to a memory area which will be written upon
* success with the received data.
*
* @param len The length in bytes of the memory area pointed to by @a
* ptr. Under normal circumstances, rt_buffer_read_timed() only
* returns entire messages as specified by the @a len argument, or an
* error value. However, short reads are allowed when a potential
* deadlock situation is detected (see note below).
*
* @param abs_timeout An absolute date expressed in clock ticks,
* specifying a time limit to wait for a message to be available from
* the buffer (see note). Passing NULL causes the caller to block
* indefinitely until enough data is available. Passing { .tv_sec = 0,
* .tv_nsec = 0 } causes the service to return immediately without
* blocking in case not enough data is available.
*
* @return The number of bytes read from the buffer is returned upon
* success. Otherwise:
*
* - -ETIMEDOUT is returned if @a abs_timeout is reached before a
* complete message arrives.
*
* - -EWOULDBLOCK is returned if @a abs_timeout is { .tv_sec = 0,
* .tv_nsec = 0 } and not enough data is immediately available on
* entry to form a complete message.
* - -EINTR is returned if rt_task_unblock() was called for the
* current task before enough data became available to form a complete
* message.
*
* - -EINVAL is returned if @a bf is not a valid buffer descriptor, or
* @a len is greater than the actual buffer length.
*
* - -EIDRM is returned if @a bf is deleted while the caller was
* waiting for data. In such event, @a bf is no more valid upon return
* of this service.
*
* - -EPERM is returned if this service should block, but was not
* called from a Xenomai thread.
*
* @note A short read (i.e. fewer bytes returned than requested by @a
* len) may happen whenever a pathological use of the buffer is
* encountered. This condition only arises when the system detects
* that one or more writers are waiting for sending data, while a
* reader would have to wait for receiving a complete message at the
* same time. For instance, consider the following sequence, involving
* a 1024-byte buffer (bf) and two threads:
*
* writer thread > rt_write_buffer(&bf, ptr, 1, TM_INFINITE);
* (one byte to read, 1023 bytes available for sending)
* writer thread > rt_write_buffer(&bf, ptr, 1024, TM_INFINITE);
* (writer blocks - no space for another 1024-byte message)
* reader thread > rt_read_buffer(&bf, ptr, 1024, TM_INFINITE);
* (short read - a truncated (1-byte) message is returned)
*
* In order to prevent both threads to wait for each other
* indefinitely, a short read is allowed, which may be completed by a
* subsequent call to rt_buffer_read() or rt_buffer_read_until(). If
* that case arises, thread priorities, buffer and/or message lengths
* should likely be fixed, in order to eliminate such condition.
*
* Valid calling contexts:
*
* - Xenomai threads
* - Any other context if @a abs_timeout is { .tv_sec = 0,
* .tv_nsec = 0 }.
*
* @note @a abs_timeout is interpreted as a multiple of the Alchemy
* clock resolution (see --alchemy-clock-resolution option, defaults
* to 1 nanosecond).
*/
ssize_t rt_buffer_read_timed(RT_BUFFER *bf,
void *ptr, size_t size,
const struct timespec *abs_timeout)
{
struct alchemy_buffer_wait *wait = NULL;
struct alchemy_buffer *bcb;
struct threadobj *thobj;
size_t len, rbytes, n;
struct syncstate syns;
struct service svc;
size_t rdoff;
int ret = 0;
void *p;
len = size;
if (len == 0)
return 0;
if (!threadobj_current_p() && !alchemy_poll_mode(abs_timeout))
return -EPERM;
CANCEL_DEFER(svc);
bcb = get_alchemy_buffer(bf, &syns, &ret);
if (bcb == NULL)
goto out;
/*
* We may only return complete messages to readers, so there
* is no point in waiting for messages which are larger than
* what the buffer can hold.
*/
if (len > bcb->bufsz) {
ret = -EINVAL;
goto done;
}
redo:
for (;;) {
/*
* We should be able to read a complete message of the
* requested length, or block.
*/
if (bcb->fillsz < len)
goto wait;
/* Read from the buffer in a circular way. */
rdoff = bcb->rdoff;
rbytes = len;
p = ptr;
do {
if (rdoff + rbytes > bcb->bufsz)
n = bcb->bufsz - rdoff;
else
n = rbytes;
memcpy(p, bcb->buf + rdoff, n);
p += n;
rdoff = (rdoff + n) % bcb->bufsz;
rbytes -= n;
} while (rbytes > 0);
bcb->fillsz -= len;
bcb->rdoff = rdoff;
ret = (ssize_t)len;
/*
* Wake up all threads waiting for the buffer to
* drain, if we freed enough room for the leading one
* to post its message.
*/
thobj = syncobj_peek_drain(&bcb->sobj);
if (thobj == NULL)
goto done;
wait = threadobj_get_wait(thobj);
if (wait->size + bcb->fillsz <= bcb->bufsz)
syncobj_drain(&bcb->sobj);
goto done;
wait:
if (alchemy_poll_mode(abs_timeout)) {
ret = -EWOULDBLOCK;
goto done;
}
/*
* Check whether writers are already waiting for
* sending data, while we are about to wait for
* receiving some. In such a case, we have a
* pathological use of the buffer. We must allow for a
* short read to prevent a deadlock.
*/
if (bcb->fillsz > 0 && syncobj_count_drain(&bcb->sobj)) {
len = bcb->fillsz;
goto redo;
}
if (wait == NULL)
wait = threadobj_prepare_wait(struct alchemy_buffer_wait);
wait->size = len;
ret = syncobj_wait_grant(&bcb->sobj, abs_timeout, &syns);
if (ret) {
if (ret == -EIDRM)
goto out;
break;
}
}
done:
put_alchemy_buffer(bcb, &syns);
out:
if (wait)
threadobj_finish_wait();
CANCEL_RESTORE(svc);
return ret;
}
