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Switch read and write functions to use cached timespec timeouts, new operator functions, and pselect in place of select.

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This commit is contained in:
Mike Purvis 2013-10-06 11:19:47 -04:00
parent 452dd3e678
commit 88b628ba98
2 changed files with 44 additions and 87 deletions
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2
include/serial/impl/unix.h
View File

@ -31,7 +31,7 @@
* \section DESCRIPTION
*
* This provides a unix based pimpl for the Serial class. This implementation is
* based off termios.h and uses select for multiplexing the IO ports.
* based off termios.h and uses pselect for multiplexing the IO ports.
*
*/

127
src/impl/unix.cc
View File

@ -60,6 +60,8 @@ Serial::SerialImpl::SerialImpl (const string &port, unsigned long baudrate,
{
pthread_mutex_init(&this->read_mutex, NULL);
pthread_mutex_init(&this->write_mutex, NULL);
serial::Timeout zero_timeout;
setTimeout(zero_timeout);
if (port_.empty () == false)
open ();
}
@ -404,61 +406,27 @@ Serial::SerialImpl::read (uint8_t *buf, size_t size)
if (!is_open_) {
throw PortNotOpenedException ("Serial::read");
}
fd_set readfds;
// Add the total timeout time to the current time, and mark that as the
// overall expiry point for the function.
struct timespec timeout_endtime(timespec_now() +
read_timeout_constant_ + (read_timeout_multiplier_ * size));
size_t bytes_read = 0;
// Setup the total_timeout timeval
// This timeout is maximum time before a timeout after read is called
struct timeval total_timeout;
// Calculate total timeout in milliseconds t_c + (t_m * N)
long total_timeout_ms = timeout_.read_timeout_constant;
total_timeout_ms += timeout_.read_timeout_multiplier*static_cast<long>(size);
total_timeout.tv_sec = total_timeout_ms / 1000;
total_timeout.tv_usec = static_cast<int>(total_timeout_ms % 1000);
total_timeout.tv_usec *= 1000; // To convert to micro seconds
// Setup the inter byte timeout
struct timeval inter_byte_timeout;
inter_byte_timeout.tv_sec = timeout_.inter_byte_timeout / 1000;
inter_byte_timeout.tv_usec =
static_cast<int> (timeout_.inter_byte_timeout % 1000);
inter_byte_timeout.tv_usec *= 1000; // To convert to micro seconds
while (bytes_read < size) {
// Setup the select timeout timeval
struct timeval timeout;
// If the total_timeout is less than the inter_byte_timeout
if (total_timeout.tv_sec < inter_byte_timeout.tv_sec
|| (total_timeout.tv_sec == inter_byte_timeout.tv_sec
&& total_timeout.tv_usec < inter_byte_timeout.tv_sec))
{
// Then set the select timeout to use the total time
timeout = total_timeout;
} else {
// Else set the select timeout to use the inter byte time
timeout = inter_byte_timeout;
}
// Must determine whether the time remaining before endtime (total read
// timeout) or the inter-byte timeout is sooner, and use that one as the
// timeout for the pselect call.
struct timespec timeout_remaining(timeout_endtime - timespec_now());
struct timespec timeout(min(timeout_remaining, inter_byte_timeout_));
// Call pselect to block for serial data or a timeout
fd_set readfds;
FD_ZERO (&readfds);
FD_SET (fd_, &readfds);
// Begin timing select
struct timespec start(get_time_now());
// Call select to block for serial data or a timeout
int r = select (fd_ + 1, &readfds, NULL, NULL, &timeout);
// Calculate difference and update the structure
struct timespec end(get_time_now());
// Calculate the time select took
struct timespec diff(end - start);
int r = pselect (fd_ + 1, &readfds, NULL, NULL, &timeout, NULL);
// Update the timeout
if (total_timeout.tv_sec <= diff.tv_sec) {
total_timeout.tv_sec = 0;
} else {
total_timeout.tv_sec -= diff.tv_sec;
}
if (total_timeout.tv_usec <= (diff.tv_nsec / 1000)) {
total_timeout.tv_usec = 0;
} else {
total_timeout.tv_usec -= (diff.tv_nsec / 1000);
}
// Figure out what happened by looking at select's response 'r'
// Figure out what happened by looking at pselect's response 'r'
/** Error **/
if (r < 0) {
// Select was interrupted, try again
@ -477,10 +445,10 @@ Serial::SerialImpl::read (uint8_t *buf, size_t size)
// Make sure our file descriptor is in the ready to read list
if (FD_ISSET (fd_, &readfds)) {
// This should be non-blocking returning only what is available now
// Then returning so that select can block again.
// Then returning so that pselect can block again.
ssize_t bytes_read_now =
::read (fd_, buf + bytes_read, size - bytes_read);
// read should always return some data as select reported it was
// read should always return some data as pselect reported it was
// ready to read when we get to this point.
if (bytes_read_now < 1) {
// Disconnected devices, at least on Linux, show the
@ -507,7 +475,7 @@ Serial::SerialImpl::read (uint8_t *buf, size_t size)
}
}
// This shouldn't happen, if r > 0 our fd has to be in the list!
THROW (IOException, "select reports ready to read, but our fd isn't"
THROW (IOException, "pselect reports ready to read, but our fd isn't"
" in the list, this shouldn't happen!");
}
}
@ -520,41 +488,22 @@ Serial::SerialImpl::write (const uint8_t *data, size_t length)
if (is_open_ == false) {
throw PortNotOpenedException ("Serial::write");
}
fd_set writefds;
// Add the total timeout time to the current time, and mark that as the
// overall expiry point for the function.
struct timespec timeout_endtime(timespec_now() +
write_timeout_constant_ + (write_timeout_multiplier_ * length));
size_t bytes_written = 0;
struct timeval timeout;
timeout.tv_sec = timeout_.write_timeout_constant / 1000;
timeout.tv_usec = static_cast<int> (timeout_.write_timeout_multiplier % 1000);
timeout.tv_usec *= 1000; // To convert to micro seconds
while (bytes_written < length) {
// Determine time remaining before the predetermined endpoint.
struct timespec timeout_remaining(timeout_endtime - timespec_now());
// Call pselect to wait on availability of port for writing.
fd_set writefds;
FD_ZERO (&writefds);
FD_SET (fd_, &writefds);
// On Linux the timeout struct is updated by select to contain the time
// left on the timeout to make looping easier, but on other platforms this
// does not occur.
#if !defined(__linux__)
// Begin timing select
struct timespec start(get_time_now());
#endif
// Do the select
int r = select (fd_ + 1, NULL, &writefds, NULL, &timeout);
#if !defined(__linux__)
// Calculate difference and update the structure
struct timespec end(get_time_now());
// Calculate the time select took
struct timespec diff(end - start);
// Update the timeout
if (timeout.tv_sec <= diff.tv_sec) {
timeout.tv_sec = 0;
} else {
timeout.tv_sec -= diff.tv_sec;
}
if (timeout.tv_usec <= (diff.tv_nsec / 1000)) {
timeout.tv_usec = 0;
} else {
timeout.tv_usec -= (diff.tv_nsec / 1000);
}
#endif
int r = pselect (fd_ + 1, NULL, &writefds, NULL, &timeout_remaining, NULL);
// Figure out what happened by looking at select's response 'r'
/** Error **/
@ -624,9 +573,17 @@ Serial::SerialImpl::getPort () const
}
void
Serial::SerialImpl::setTimeout (serial::Timeout &timeout)
Serial::SerialImpl::setTimeout (const serial::Timeout &timeout)
{
timeout_ = timeout;
// Cache the timespec conversions, as that's what the rest of the inner
// class operates on.
inter_byte_timeout_ = timespec_from_millis(timeout.inter_byte_timeout);
read_timeout_constant_ = timespec_from_millis(timeout.read_timeout_constant);
read_timeout_multiplier_ = timespec_from_millis(timeout.read_timeout_constant);
write_timeout_constant_ = timespec_from_millis(timeout.write_timeout_constant);
write_timeout_multiplier_ = timespec_from_millis(timeout.write_timeout_multiplier);
}
serial::Timeout