Reject a sweep threshold outside the slot-table capacity

An override above SHARED_REGION_MAX_PROCESS_NUM would keep the sweep from
ever running, so a table full of dead slots would reach the capacity check
and exit -- the case this branch set out to make recoverable. Zero would
sweep on every join and bring back the cost this branch removes. Catch both
at compile time, since the override only exists for the regression test.

Signed-off-by: keshav9926 <kkakani160@gmail.com>

Author: keshav9926

src/multiprocess/multiprocess_memory_limit.h

@@ -46,6 +46,12 @@
 #ifndef SHARED_REGION_SWEEP_THRESHOLD
     #define SHARED_REGION_SWEEP_THRESHOLD ((SHARED_REGION_MAX_PROCESS_NUM * 3) / 4)
 #endif
+// Past capacity the sweep could never run, so a table full of dead slots would
+// reach the capacity check and exit. At zero every join sweeps again.
+#if SHARED_REGION_SWEEP_THRESHOLD < 1 || \
+    SHARED_REGION_SWEEP_THRESHOLD > SHARED_REGION_MAX_PROCESS_NUM
+    #error "SHARED_REGION_SWEEP_THRESHOLD must be between 1 and SHARED_REGION_MAX_PROCESS_NUM"
+#endif
 
 // macros for debugging
 #define SEQ_FIX_SHRREG_ACQUIRE_FLOCK_OK 0