Tcl Source Code

In TclUnixWaitForFile() (unix/tclUnixNotfy.c) now is only assigned if timeout > 0, but the loop is

    do {
	...
	if (timeout < 0) {
	    continue;
	}
	now = Tcl_GetDayTime();
    } while (abortTime > now);

continue in a do-while jumps to the condition, so with timeout < 0 (wait forever), whenever poll() returns without a requested event (e.g. -1 with EINTR on a signal, or POLLNVAL), abortTime > now is evaluated with abortTime == 0 and an uninitialized now. Depending on the garbage value the function either waits again or returns 0 ("not ready") although the wait was infinite. GCC reports it as "'now' may be used uninitialized" (seen with gcc 8.3 on DragonFly and gcc 10.5 on NetBSD), although at the first use at line 595, which is guarded by timeout > 0.

WaitForConnect() in tclUnixSock.c calls it with -1 in a loop, which hides the early return there, but other callers (it is in the internal stubs table) are affected. 9.0 has the same loop (with Tcl_Time); 8.6 uses while (1) and is not affected.