Windows nonblocking write: 1 byte at a time to know when buffer fills.

[libserialport.git] / serialport.c

diff --git a/serialport.c b/serialport.c
index bb5e90a5850ce5bb2399abcfa5838e357ca5279f..9d2a50440046fd67642cd91431f3e55398aa4f29 100644 (file)
--- a/serialport.c
+++ b/serialport.c
@@ -63,6 +63,9 @@ struct sp_port {
        int nonblocking;
 #ifdef _WIN32
        HANDLE hdl;
+       OVERLAPPED write_ovl;
+       BYTE pending_byte;
+       BOOL writing;
 #else
        int fd;
 #endif
@@ -583,6 +586,7 @@ enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
 
 #ifdef _WIN32
        DWORD desired_access = 0, flags_and_attributes = 0;
+       COMMTIMEOUTS timeouts;
        char *escaped_port_name;
 
        /* Prefix port name with '\\.\' to work with ports above COM9. */
@@ -606,6 +610,30 @@ enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
 
        if (port->hdl == INVALID_HANDLE_VALUE)
                RETURN_FAIL("CreateFile() failed");
+
+       /* All timeouts disabled. */
+       timeouts.ReadIntervalTimeout = 0;
+       timeouts.ReadTotalTimeoutMultiplier = 0;
+       timeouts.ReadTotalTimeoutConstant = 0;
+       timeouts.WriteTotalTimeoutMultiplier = 0;
+       timeouts.WriteTotalTimeoutConstant = 0;
+
+       if (port->nonblocking) {
+               /* Set read timeout such that all reads return immediately. */
+               timeouts.ReadIntervalTimeout = MAXDWORD;
+               /* Prepare OVERLAPPED structure for non-blocking writes. */
+               memset(&port->write_ovl, 0, sizeof(port->write_ovl));
+               if (!(port->write_ovl.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL))) {
+                       sp_close(port);
+                       RETURN_FAIL("CreateEvent() failed");
+               }
+               port->writing = FALSE;
+       }
+
+       if (SetCommTimeouts(port->hdl, &timeouts) == 0) {
+               sp_close(port);
+               RETURN_FAIL("SetCommTimeouts() failed");
+       }
 #else
        int flags_local = 0;
        struct port_data data;
@@ -668,6 +696,11 @@ enum sp_return sp_close(struct sp_port *port)
        if (CloseHandle(port->hdl) == 0)
                RETURN_FAIL("CloseHandle() failed");
        port->hdl = INVALID_HANDLE_VALUE;
+       if (port->nonblocking) {
+               /* Close event handle created for overlapped writes. */
+               if (CloseHandle(port->write_ovl.hEvent) == 0)
+                       RETURN_FAIL("CloseHandle() failed");
+       }
 #else
        /* Returns 0 upon success, -1 upon failure. */
        if (close(port->fd) == -1)
@@ -749,12 +782,60 @@ enum sp_return sp_write(struct sp_port *port, const void *buf, size_t count)
 
        DEBUG("Writing up to %d bytes to port %s", count, port->name);
 
+       if (count == 0)
+               RETURN_VALUE("0", 0);
+
 #ifdef _WIN32
        DWORD written = 0;
+       BYTE *ptr = (BYTE *) buf;
+
+       if (port->nonblocking) {
+               /* Non-blocking write. */
+
+               /* Check whether previous write is complete. */
+               if (port->writing) {
+                       if (HasOverlappedIoCompleted(&port->write_ovl)) {
+                               DEBUG("Previous write completed");
+                               port->writing = 0;
+                       } else {
+                               DEBUG("Previous write not complete");
+                               /* Can't take a new write until the previous one finishes. */
+                               RETURN_VALUE("0", 0);
+                       }
+               }
+
+               /* Keep writing data until the OS has to actually start an async IO for it.
+                * At that point we know the buffer is full. */
+               while (written < count)
+               {
+                       /* Copy first byte of user buffer. */
+                       port->pending_byte = *ptr++;
+
+                       /* Start asynchronous write. */
+                       if (WriteFile(port->hdl, &port->pending_byte, 1, NULL, &port->write_ovl) == 0) {
+                               if (GetLastError() == ERROR_IO_PENDING) {
+                                       DEBUG("Asynchronous write started");
+                                       port->writing = 1;
+                                       RETURN_VALUE("%d", ++written);
+                               } else {
+                                       /* Actual failure of some kind. */
+                                       RETURN_FAIL("WriteFile() failed");
+                               }
+                       } else {
+                               DEBUG("Single byte written immediately.");
+                               written++;
+                       }
+               }
+
+               DEBUG("All bytes written immediately.");
+
+       } else {
+               /* Blocking write. */
+               if (WriteFile(port->hdl, buf, count, &written, NULL) == 0) {
+                       RETURN_FAIL("WriteFile() failed");
+               }
+       }
 
-       /* Returns non-zero upon success, 0 upon failure. */
-       if (WriteFile(port->hdl, buf, count, &written, NULL) == 0)
-               RETURN_FAIL("WriteFile() failed");
        RETURN_VALUE("%d", written);
 #else
        /* Returns the number of bytes written, or -1 upon failure. */