Assert that WaitLatch's timeout is not more than INT_MAX milliseconds.

The behavior with larger values is unspecified by the Single Unix Spec.
It appears that BSD-derived kernels report EINVAL, although Linux does not.
If waiting for longer intervals is desired, the calling code has to do
something to limit the delay; we can't portably fix it here since "long"
may not be any wider than "int" in the first place.

Part of response to bug #7670, though this change doesn't fix that
(in fact, it converts the problem from an ERROR into an Assert failure).
No back-patch since it's just an assertion addition.

src/backend/port/unix_latch.c

@@ -33,6 +33,7 @@
 #include "postgres.h"
 
 #include <fcntl.h>
+#include <limits.h>
 #include <signal.h>
 #include <unistd.h>
 #include <sys/time.h>
@@ -176,9 +177,10 @@ DisownLatch(volatile Latch *latch)
  * to wait for. If the latch is already set (and WL_LATCH_SET is given), the
  * function returns immediately.
  *
- * The 'timeout' is given in milliseconds. It must be >= 0 if WL_TIMEOUT flag
- * is given.  Note that some extra overhead is incurred when WL_TIMEOUT is
- * given, so avoid using a timeout if possible.
+ * The "timeout" is given in milliseconds. It must be >= 0 if WL_TIMEOUT flag
+ * is given.  Although it is declared as "long", we don't actually support
+ * timeouts longer than INT_MAX milliseconds.  Note that some extra overhead
+ * is incurred when WL_TIMEOUT is given, so avoid using a timeout if possible.
  *
  * The latch must be owned by the current process, ie. it must be a
  * backend-local latch initialized with InitLatch, or a shared latch
@@ -243,7 +245,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 	if (wakeEvents & WL_TIMEOUT)
 	{
 		INSTR_TIME_SET_CURRENT(start_time);
-		Assert(timeout >= 0);
+		Assert(timeout >= 0 && timeout <= INT_MAX);
 		cur_timeout = timeout;
 
 #ifndef HAVE_POLL

src/backend/port/win32_latch.c

@@ -20,6 +20,7 @@
 #include "postgres.h"
 
 #include <fcntl.h>
+#include <limits.h>
 #include <signal.h>
 #include <unistd.h>
 
@@ -130,7 +131,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 	if (wakeEvents & WL_TIMEOUT)
 	{
 		INSTR_TIME_SET_CURRENT(start_time);
-		Assert(timeout >= 0);
+		Assert(timeout >= 0 && timeout <= INT_MAX);
 		cur_timeout = timeout;
 	}
 	else