posix: Make sure blocking operations can't time out without trying.

diff --git a/serialport.c b/serialport.c
index c77682f98566fcf903e8aa76689949cdc4b8523c..8599de137254fd4ab4de956772427c3c9dbdd109 100644 (file)
--- a/serialport.c
+++ b/serialport.c
@@ -774,6 +774,7 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
        size_t bytes_written = 0;
        unsigned char *ptr = (unsigned char *) buf;
        struct timeval start, delta, now, end = {0, 0};
+       int started = 0;
        fd_set fds;
        int result;
 
@@ -792,8 +793,12 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
 
        /* Loop until we have written the requested number of bytes. */
        while (bytes_written < count) {
-               /* Wait until space is available. */
-               if (timeout_ms) {
+               /*
+                * Check timeout only if we have run select() at least once,
+                * to avoid any issues if a short timeout is reached before
+                * select() is even run.
+                */
+               if (timeout_ms && started) {
                        gettimeofday(&now, NULL);
                        if (timercmp(&now, &end, >))
                                /* Timeout has expired. */
@@ -801,6 +806,7 @@ SP_API enum sp_return sp_blocking_write(struct sp_port *port, const void *buf,
                        timersub(&end, &now, &delta);
                }
                result = select(port->fd + 1, NULL, &fds, NULL, timeout_ms ? &delta : NULL);
+               started = 1;
                if (result < 0) {
                        if (errno == EINTR) {
                                DEBUG("select() call was interrupted, repeating");
@@ -992,6 +998,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
        size_t bytes_read = 0;
        unsigned char *ptr = (unsigned char *) buf;
        struct timeval start, delta, now, end = {0, 0};
+       int started = 0;
        fd_set fds;
        int result;
 
@@ -1010,8 +1017,12 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
 
        /* Loop until we have the requested number of bytes. */
        while (bytes_read < count) {
-               /* Wait until data is available. */
-               if (timeout_ms) {
+               /*
+                * Check timeout only if we have run select() at least once,
+                * to avoid any issues if a short timeout is reached before
+                * select() is even run.
+                */
+               if (timeout_ms && started) {
                        gettimeofday(&now, NULL);
                        if (timercmp(&now, &end, >))
                                /* Timeout has expired. */
@@ -1019,6 +1030,7 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
                        timersub(&end, &now, &delta);
                }
                result = select(port->fd + 1, &fds, NULL, NULL, timeout_ms ? &delta : NULL);
+               started = 1;
                if (result < 0) {
                        if (errno == EINTR) {
                                DEBUG("select() call was interrupted, repeating");
@@ -1036,7 +1048,10 @@ SP_API enum sp_return sp_blocking_read(struct sp_port *port, void *buf,
 
                if (result < 0) {
                        if (errno == EAGAIN)
-                               /* This shouldn't happen because we did a select() first, but handle anyway. */
+                               /*
+                                * This shouldn't happen because we did a
+                                * select() first, but handle anyway.
+                                */
                                continue;
                        else
                                /* This is an actual failure. */
@@ -1267,6 +1282,7 @@ SP_API enum sp_return sp_wait(struct sp_event_set *event_set,
        RETURN_OK();
 #else
        struct timeval start, delta, now, end = {0, 0};
+       int started = 0;
        int result, timeout_remaining_ms;
        struct pollfd *pollfds;
        unsigned int i;
@@ -1298,7 +1314,12 @@ SP_API enum sp_return sp_wait(struct sp_event_set *event_set,
 
        /* Loop until an event occurs. */
        while (1) {
-               if (timeout_ms) {
+               /*
+                * Check timeout only if we have run poll() at least once,
+                * to avoid any issues if a short timeout is reached before
+                * poll() is even run.
+                */
+               if (timeout_ms && started) {
                        gettimeofday(&now, NULL);
                        if (timercmp(&now, &end, >)) {
                                DEBUG("Wait timed out");
@@ -1309,6 +1330,7 @@ SP_API enum sp_return sp_wait(struct sp_event_set *event_set,
                }
 
                result = poll(pollfds, event_set->count, timeout_ms ? timeout_remaining_ms : -1);
+               started = 1;
 
                if (result < 0) {
                        if (errno == EINTR) {