1 files changed, 194 insertions, 0 deletions
diff --git a/src/backend/postmaster/auxprocess.c b/src/backend/postmaster/auxprocess.c
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+/*-------------------------------------------------------------------------
+ * auxprocess.c
+ *	  functions related to auxiliary processes.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/auxprocess.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+#include <signal.h>
+
+#include "libpq/pqsignal.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "postmaster/auxprocess.h"
+#include "postmaster/bgwriter.h"
+#include "postmaster/startup.h"
+#include "postmaster/walwriter.h"
+#include "replication/walreceiver.h"
+#include "storage/bufmgr.h"
+#include "storage/bufpage.h"
+#include "storage/condition_variable.h"
+#include "storage/ipc.h"
+#include "storage/proc.h"
+#include "tcop/tcopprot.h"
+#include "utils/memutils.h"
+#include "utils/ps_status.h"
+#include "utils/rel.h"
+
+
+static void ShutdownAuxiliaryProcess(int code, Datum arg);
+
+
+/* ----------------
+ *		global variables
+ * ----------------
+ */
+
+AuxProcType MyAuxProcType = NotAnAuxProcess;	/* declared in miscadmin.h */
+
+
+/*
+ *	 AuxiliaryProcessMain
+ *
+ *	 The main entry point for auxiliary processes, such as the bgwriter,
+ *	 walwriter, walreceiver, bootstrapper and the shared memory checker code.
+ *
+ *	 This code is here just because of historical reasons.
+ */
+void
+AuxiliaryProcessMain(AuxProcType auxtype)
+{
+	Assert(IsUnderPostmaster);
+
+	MyAuxProcType = auxtype;
+
+	switch (MyAuxProcType)
+	{
+		case StartupProcess:
+			MyBackendType = B_STARTUP;
+			break;
+		case ArchiverProcess:
+			MyBackendType = B_ARCHIVER;
+			break;
+		case BgWriterProcess:
+			MyBackendType = B_BG_WRITER;
+			break;
+		case CheckpointerProcess:
+			MyBackendType = B_CHECKPOINTER;
+			break;
+		case WalWriterProcess:
+			MyBackendType = B_WAL_WRITER;
+			break;
+		case WalReceiverProcess:
+			MyBackendType = B_WAL_RECEIVER;
+			break;
+		default:
+			elog(ERROR, "something has gone wrong");
+			MyBackendType = B_INVALID;
+	}
+
+	init_ps_display(NULL);
+
+	SetProcessingMode(BootstrapProcessing);
+	IgnoreSystemIndexes = true;
+
+	BaseInit();
+
+	/*
+	 * As an auxiliary process, we aren't going to do the full InitPostgres
+	 * pushups, but there are a couple of things that need to get lit up even
+	 * in an auxiliary process.
+	 */
+
+	/*
+	 * Create a PGPROC so we can use LWLocks.  In the EXEC_BACKEND case, this
+	 * was already done by SubPostmasterMain().
+	 */
+#ifndef EXEC_BACKEND
+	InitAuxiliaryProcess();
+#endif
+
+	/*
+	 * Assign the ProcSignalSlot for an auxiliary process.  Since it doesn't
+	 * have a BackendId, the slot is statically allocated based on the
+	 * auxiliary process type (MyAuxProcType).  Backends use slots indexed in
+	 * the range from 1 to MaxBackends (inclusive), so we use MaxBackends +
+	 * AuxProcType + 1 as the index of the slot for an auxiliary process.
+	 *
+	 * This will need rethinking if we ever want more than one of a particular
+	 * auxiliary process type.
+	 */
+	ProcSignalInit(MaxBackends + MyAuxProcType + 1);
+
+	/* finish setting up bufmgr.c */
+	InitBufferPoolBackend();
+
+	/*
+	 * Auxiliary processes don't run transactions, but they may need a
+	 * resource owner anyway to manage buffer pins acquired outside
+	 * transactions (and, perhaps, other things in future).
+	 */
+	CreateAuxProcessResourceOwner();
+
+	/* Initialize statistics reporting */
+	pgstat_initialize();
+
+	/* Initialize backend status information */
+	pgstat_beinit();
+	pgstat_bestart();
+
+	/* register a before-shutdown callback for LWLock cleanup */
+	before_shmem_exit(ShutdownAuxiliaryProcess, 0);
+
+	SetProcessingMode(NormalProcessing);
+
+	switch (MyAuxProcType)
+	{
+		case CheckerProcess:
+		case BootstrapProcess:
+			pg_unreachable();
+			break;
+
+		case StartupProcess:
+			StartupProcessMain();
+			proc_exit(1);
+
+		case ArchiverProcess:
+			PgArchiverMain();
+			proc_exit(1);
+
+		case BgWriterProcess:
+			BackgroundWriterMain();
+			proc_exit(1);
+
+		case CheckpointerProcess:
+			CheckpointerMain();
+			proc_exit(1);
+
+		case WalWriterProcess:
+			InitXLOGAccess();
+			WalWriterMain();
+			proc_exit(1);
+
+		case WalReceiverProcess:
+			WalReceiverMain();
+			proc_exit(1);
+
+		default:
+			elog(PANIC, "unrecognized process type: %d", (int) MyAuxProcType);
+			proc_exit(1);
+	}
+}
+
+/*
+ * Begin shutdown of an auxiliary process.  This is approximately the equivalent
+ * of ShutdownPostgres() in postinit.c.  We can't run transactions in an
+ * auxiliary process, so most of the work of AbortTransaction() is not needed,
+ * but we do need to make sure we've released any LWLocks we are holding.
+ * (This is only critical during an error exit.)
+ */
+static void
+ShutdownAuxiliaryProcess(int code, Datum arg)
+{
+	LWLockReleaseAll();
+	ConditionVariableCancelSleep();
+	pgstat_report_wait_end();
+}