1 files changed, 56 insertions, 1 deletions
diff --git a/compat/mingw.c b/compat/mingw.c
index 7f89a6cb8..2677e7862 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -101,7 +101,62 @@ int pipe(int filedes[2])
 
 int poll(struct pollfd *ufds, unsigned int nfds, int timeout)
 {
-	return -1;
+	int i, pending;
+
+	if (timeout != -1)
+		return errno = EINVAL, error("poll timeout not supported");
+
+	/* When there is only one fd to wait for, then we pretend that
+	 * input is available and let the actual wait happen when the
+	 * caller invokes read().
+	 */
+	if (nfds == 1) {
+		if (!(ufds[0].events & POLLIN))
+			return errno = EINVAL, error("POLLIN not set");
+		ufds[0].revents = POLLIN;
+		return 0;
+	}
+
+repeat:
+	pending = 0;
+	for (i = 0; i < nfds; i++) {
+		DWORD avail = 0;
+		HANDLE h = (HANDLE) _get_osfhandle(ufds[i].fd);
+		if (h == INVALID_HANDLE_VALUE)
+			return -1;	/* errno was set */
+
+		if (!(ufds[i].events & POLLIN))
+			return errno = EINVAL, error("POLLIN not set");
+
+		/* this emulation works only for pipes */
+		if (!PeekNamedPipe(h, NULL, 0, NULL, &avail, NULL)) {
+			int err = GetLastError();
+			if (err == ERROR_BROKEN_PIPE) {
+				ufds[i].revents = POLLHUP;
+				pending++;
+			} else {
+				errno = EINVAL;
+				return error("PeekNamedPipe failed,"
+					" GetLastError: %u", err);
+			}
+		} else if (avail) {
+			ufds[i].revents = POLLIN;
+			pending++;
+		} else
+			ufds[i].revents = 0;
+	}
+	if (!pending) {
+		/* The only times that we spin here is when the process
+		 * that is connected through the pipes is waiting for
+		 * its own input data to become available. But since
+		 * the process (pack-objects) is itself CPU intensive,
+		 * it will happily pick up the time slice that we are
+		 * relinguishing here.
+		 */
+		Sleep(0);
+		goto repeat;
+	}
+	return 0;
 }
 
 struct tm *gmtime_r(const time_t *timep, struct tm *result)