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_modbus_receive_msg: use a deadline for the receive timeout #882

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_modbus_receive_msg: use a deadline for the receive timeout #882

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39 changes: 37 additions & 2 deletions src/modbus.c
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,24 @@ void _error_print(modbus_t *ctx, const char *context)
}
}

/* Monotonic time in microseconds */
static int64_t _modbus_time_usec(void)
{
#ifdef _WIN32
LARGE_INTEGER freq, now;

QueryPerformanceFrequency(&freq);
QueryPerformanceCounter(&now);
return (int64_t) (now.QuadPart / freq.QuadPart) * 1000000 +
(int64_t) (now.QuadPart % freq.QuadPart) * 1000000 / freq.QuadPart;
#else
struct timespec ts;

clock_gettime(CLOCK_MONOTONIC, &ts);
return (int64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
#endif
}

static void _sleep_response_timeout(modbus_t *ctx)
{
/* Response timeout is always positive */
Expand Down Expand Up @@ -368,6 +386,7 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
fd_set rset;
struct timeval tv;
struct timeval *p_tv;
int64_t deadline = 0;
unsigned int length_to_read;
int msg_length = 0;
_step_t step;
Expand Down Expand Up @@ -425,7 +444,22 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
p_tv = &tv;
}

if (p_tv != NULL) {
deadline = _modbus_time_usec() + (int64_t) tv.tv_sec * 1000000 + tv.tv_usec;
}

while (length_to_read != 0) {
if (deadline != 0) {
/* Only Linux updates the timeout passed to select(), so give it
what is left before the deadline */
int64_t remaining = deadline - _modbus_time_usec();

if (remaining < 0) {
remaining = 0;
}
tv.tv_sec = (long) (remaining / 1000000);
tv.tv_usec = (long) (remaining % 1000000);
}
rc = ctx->backend->select(ctx, &rset, p_tv, length_to_read);
if (rc == -1) {
_error_print(ctx, "select");
Expand Down Expand Up @@ -535,9 +569,10 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
tv.tv_sec = ctx->byte_timeout.tv_sec;
tv.tv_usec = ctx->byte_timeout.tv_usec;
p_tv = &tv;
deadline = 0;
}
/* else timeout isn't set again, the full response must be read before
expiration of response timeout (for CONFIRMATION only) */
/* else the whole message must be read before the deadline set from the
response or indication timeout */
}

if (ctx->debug)
Expand Down
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