Use PostmasterRandom(), not random(), for DSM control segment ID.

Otherwise, every startup gets the same "random" value, which is
definitely not what was intended.

src/backend/postmaster/postmaster.c

@@ -403,7 +403,6 @@ static void processCancelRequest(Port *port, void *pkt);
 static int	initMasks(fd_set *rmask);
 static void report_fork_failure_to_client(Port *port, int errnum);
 static CAC_state canAcceptConnections(void);
-static long PostmasterRandom(void);
 static void RandomSalt(char *salt, int len);
 static void signal_child(pid_t pid, int signal);
 static bool SignalSomeChildren(int signal, int targets);
@@ -5101,7 +5100,7 @@ RandomSalt(char *salt, int len)
 /*
  * PostmasterRandom
  */
-static long
+long
 PostmasterRandom(void)
 {
 	/*

src/backend/storage/ipc/dsm.c

@@ -36,6 +36,7 @@
 
 #include "lib/ilist.h"
 #include "miscadmin.h"
+#include "postmaster/postmaster.h"
 #include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/lwlock.h"
@@ -181,7 +182,7 @@ dsm_postmaster_startup(PGShmemHeader *shim)
 	{
 		Assert(dsm_control_address == NULL);
 		Assert(dsm_control_mapped_size == 0);
-		dsm_control_handle = random();
+		dsm_control_handle = (dsm_handle) PostmasterRandom();
 		if (dsm_control_handle == 0)
 			continue;
 		if (dsm_impl_op(DSM_OP_CREATE, dsm_control_handle, segsize,

src/include/postmaster/postmaster.h

@@ -48,6 +48,7 @@ extern const char *progname;
 
 extern void PostmasterMain(int argc, char *argv[]) pg_attribute_noreturn();
 extern void ClosePostmasterPorts(bool am_syslogger);
+extern long PostmasterRandom(void);
 
 extern int	MaxLivePostmasterChildren(void);