v01_add_checking_infrastracture.patch

diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index aac10165ec..0c4d61a34c 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -269,6 +269,7 @@ CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
 
 			readmessage:
 					HOLD_CANCEL_INTERRUPTS();
+					HOLD_CHECKING_REMOTE_SERVERS_INTERRUPTS();
 					pq_startmsgread();
 					mtype = pq_getbyte();
 					if (mtype == EOF)
@@ -300,6 +301,7 @@ CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
 						ereport(ERROR,
 								(errcode(ERRCODE_CONNECTION_FAILURE),
 								 errmsg("unexpected EOF on client connection with an open transaction")));
+					RESUME_CHECKING_REMOTE_SERVERS_INTERRUPTS();
 					RESUME_CANCEL_INTERRUPTS();
 					/* ... and process it */
 					switch (mtype)
diff --git a/src/backend/foreign/foreign.c b/src/backend/foreign/foreign.c
index e07cc57431..eb9c4f3f05 100644
--- a/src/backend/foreign/foreign.c
+++ b/src/backend/foreign/foreign.c
@@ -26,7 +26,11 @@
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/syscache.h"
+#include "utils/timeout.h"
 
+/* for checking remote servers */
+int remote_servers_connection_check_interval = 0;
+static CheckingRemoteServersCallbackItem *fdw_callbacks = NULL;
 
 /*
  * GetForeignDataWrapper -	look up the foreign-data wrapper by OID.
@@ -836,3 +840,51 @@ GetExistingLocalJoinPath(RelOptInfo *joinrel)
 	}
 	return NULL;
 }
+
+/*
+ * Register callbacks for checking remote servers.
+ *
+ * This function is intended for use by FDW extensions.
+ * The checking timeout will be fired after registering the first callback.
+ */
+void
+RegisterCheckingRemoteServersCallback(CheckingRemoteServersCallback callback, void *arg)
+{
+	CheckingRemoteServersCallbackItem *item;
+	/* should we start checking timeout? */
+	bool first_exec = HaveCheckingRemoteServersCallbacks();
+
+	item = (CheckingRemoteServersCallbackItem *)
+			MemoryContextAlloc(TopMemoryContext, sizeof(CheckingRemoteServersCallbackItem));
+	item->callback = callback;
+	item->arg = arg;
+	item->next = fdw_callbacks;
+	fdw_callbacks = item;
+
+	if (first_exec && remote_servers_connection_check_interval > 0)
+		enable_timeout_after(CHECKING_REMOTE_SERVERS_TIMEOUT, remote_servers_connection_check_interval);
+}
+
+
+/*
+ * Call callbacks for checking remote servers.
+ *
+ * Note that this function will not return anything.
+ * Callback functions must throw ereport(ERROR) if disconnection has been detected.
+ */
+void
+CallCheckingRemoteServersCallbacks(void)
+{
+	CheckingRemoteServersCallbackItem *item;
+	for (item = fdw_callbacks; item; item = item->next)
+		item->callback(item->arg);
+}
+
+/*
+ * Check whether any callbacks has been registered.
+ */
+bool
+HaveCheckingRemoteServersCallbacks(void)
+{
+	return fdw_callbacks != NULL;
+}
diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 89a5f901aa..31e39b6cbf 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -1159,7 +1159,6 @@ pq_startmsgread(void)
 		ereport(FATAL,
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
 				 errmsg("terminating connection because protocol synchronization was lost")));
-
 	PqCommReadingMsg = true;
 }
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 0775abe35d..d7890b5307 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -43,6 +43,7 @@
 #include "commands/async.h"
 #include "commands/prepare.h"
 #include "executor/spi.h"
+#include "foreign/foreign.h"
 #include "jit/jit.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
@@ -349,6 +350,7 @@ SocketBackend(StringInfo inBuf)
 	 * Get message type code from the frontend.
 	 */
 	HOLD_CANCEL_INTERRUPTS();
+	HOLD_CHECKING_REMOTE_SERVERS_INTERRUPTS();
 	pq_startmsgread();
 	qtype = pq_getbyte();
 
@@ -455,6 +457,7 @@ SocketBackend(StringInfo inBuf)
 	 */
 	if (pq_getmessage(inBuf, maxmsglen))
 		return EOF;				/* suitable message already logged */
+	RESUME_CHECKING_REMOTE_SERVERS_INTERRUPTS();
 	RESUME_CANCEL_INTERRUPTS();
 
 	return qtype;
@@ -2708,6 +2711,13 @@ start_xact_command(void)
 		!get_timeout_active(CLIENT_CONNECTION_CHECK_TIMEOUT))
 		enable_timeout_after(CLIENT_CONNECTION_CHECK_TIMEOUT,
 							 client_connection_check_interval);
+	if (remote_servers_connection_check_interval > 0 &&
+		IsUnderPostmaster &&
+		MyProcPort &&
+		HaveCheckingRemoteServersCallbacks() &&
+		!get_timeout_active(CHECKING_REMOTE_SERVERS_TIMEOUT))
+		enable_timeout_after(CHECKING_REMOTE_SERVERS_TIMEOUT,
+							 remote_servers_connection_check_interval);
 }
 
 static void
@@ -3213,6 +3223,24 @@ ProcessInterrupts(void)
 		}
 	}
 
+	if (CheckingRemoteServersTimeoutPending && CheckingRemoteServersHoldoffCount != 0)
+	{
+		/*
+		 * Skip checking foreign servers while reading messages.
+		 */
+		InterruptPending = true;
+	}
+	else if (CheckingRemoteServersTimeoutPending)
+	{
+		CheckingRemoteServersTimeoutPending = false;
+
+		CallCheckingRemoteServersCallbacks();
+
+		if (remote_servers_connection_check_interval > 0)
+			enable_timeout_after(CHECKING_REMOTE_SERVERS_TIMEOUT,
+									remote_servers_connection_check_interval);
+	}
+
 	if (ClientConnectionLost)
 	{
 		QueryCancelPending = false; /* lost connection trumps QueryCancel */
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 381d9e548d..15b0c2727b 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -36,9 +36,11 @@ volatile sig_atomic_t IdleInTransactionSessionTimeoutPending = false;
 volatile sig_atomic_t IdleSessionTimeoutPending = false;
 volatile sig_atomic_t ProcSignalBarrierPending = false;
 volatile sig_atomic_t LogMemoryContextPending = false;
+volatile sig_atomic_t CheckingRemoteServersTimeoutPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
 volatile uint32 CritSectionCount = 0;
+volatile uint32 CheckingRemoteServersHoldoffCount = 0;
 
 int			MyProcPid;
 pg_time_t	MyStartTime;
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 78bc64671e..fcf5d24248 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -73,6 +73,7 @@ static void LockTimeoutHandler(void);
 static void IdleInTransactionSessionTimeoutHandler(void);
 static void IdleSessionTimeoutHandler(void);
 static void ClientCheckTimeoutHandler(void);
+static void CheckingRemoteServersTimeoutHandler(void);
 static bool ThereIsAtLeastOneRole(void);
 static void process_startup_options(Port *port, bool am_superuser);
 static void process_settings(Oid databaseid, Oid roleid);
@@ -615,6 +616,7 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 						IdleInTransactionSessionTimeoutHandler);
 		RegisterTimeout(IDLE_SESSION_TIMEOUT, IdleSessionTimeoutHandler);
 		RegisterTimeout(CLIENT_CONNECTION_CHECK_TIMEOUT, ClientCheckTimeoutHandler);
+		RegisterTimeout(CHECKING_REMOTE_SERVERS_TIMEOUT, CheckingRemoteServersTimeoutHandler);
 	}
 
 	/*
@@ -1245,6 +1247,14 @@ ClientCheckTimeoutHandler(void)
 	SetLatch(MyLatch);
 }
 
+static void
+CheckingRemoteServersTimeoutHandler(void)
+{
+	CheckingRemoteServersTimeoutPending = true;
+	InterruptPending = true;
+	SetLatch(MyLatch);
+}
+
 /*
  * Returns true if at least one role is defined in this database cluster.
  */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index e91d5a3cfd..24172de7a9 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -51,6 +51,7 @@
 #include "commands/vacuum.h"
 #include "commands/variable.h"
 #include "common/string.h"
+#include "foreign/foreign.h"
 #include "funcapi.h"
 #include "jit/jit.h"
 #include "libpq/auth.h"
@@ -105,6 +106,7 @@
 #include "utils/queryjumble.h"
 #include "utils/rls.h"
 #include "utils/snapmgr.h"
+#include "utils/timeout.h"
 #include "utils/tzparser.h"
 #include "utils/inval.h"
 #include "utils/varlena.h"
@@ -3583,6 +3585,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+
+	{
+		{"remote_servers_connection_check_interval", PGC_USERSET, CONN_AUTH_SETTINGS,
+			gettext_noop("Sets the time interval between checks for disconnection of remote servers."),
+			NULL,
+			GUC_UNIT_MS
+		},
+		&remote_servers_connection_check_interval,
+		0, 0, INT_MAX,
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 1cbc9feeb6..9b70761d9c 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -90,6 +90,10 @@
 					# disconnection while running queries;
 					# 0 for never
 
+#remote_servers_connection_check_interval = 0	# time between time between checks for
+					# foreign server disconnection;
+					# 0 for never
+
 # - Authentication -
 
 #authentication_timeout = 1min		# 1s-600s
diff --git a/src/include/foreign/foreign.h b/src/include/foreign/foreign.h
index 8169eb76b1..98f59c1153 100644
--- a/src/include/foreign/foreign.h
+++ b/src/include/foreign/foreign.h
@@ -81,4 +81,20 @@ extern List *GetForeignColumnOptions(Oid relid, AttrNumber attnum);
 extern Oid	get_foreign_data_wrapper_oid(const char *fdwname, bool missing_ok);
 extern Oid	get_foreign_server_oid(const char *servername, bool missing_ok);
 
+
+/* functions and variables for fdw checking. */
+typedef void (*CheckingRemoteServersCallback) (void *arg);
+typedef struct CheckingRemoteServersCallbackItem
+{
+	struct CheckingRemoteServersCallbackItem *next;
+	CheckingRemoteServersCallback callback;
+	void		*arg;
+} CheckingRemoteServersCallbackItem;
+
+extern void RegisterCheckingRemoteServersCallback(CheckingRemoteServersCallback callback, void *arg);
+extern void CallCheckingRemoteServersCallbacks(void);
+extern bool HaveCheckingRemoteServersCallbacks(void);
+
+extern int remote_servers_connection_check_interval;
+
 #endif							/* FOREIGN_H */
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 90a3016065..377fc68aaa 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -98,10 +98,13 @@ extern PGDLLIMPORT volatile sig_atomic_t LogMemoryContextPending;
 extern PGDLLIMPORT volatile sig_atomic_t CheckClientConnectionPending;
 extern PGDLLIMPORT volatile sig_atomic_t ClientConnectionLost;
 
+extern PGDLLIMPORT volatile sig_atomic_t CheckingRemoteServersTimeoutPending;
+
 /* these are marked volatile because they are examined by signal handlers: */
 extern PGDLLIMPORT volatile uint32 InterruptHoldoffCount;
 extern PGDLLIMPORT volatile uint32 QueryCancelHoldoffCount;
 extern PGDLLIMPORT volatile uint32 CritSectionCount;
+extern PGDLLIMPORT volatile uint32 CheckingRemoteServersHoldoffCount;
 
 /* in tcop/postgres.c */
 extern void ProcessInterrupts(void);
@@ -126,7 +129,7 @@ do { \
 /* Is ProcessInterrupts() guaranteed to clear InterruptPending? */
 #define INTERRUPTS_CAN_BE_PROCESSED() \
 	(InterruptHoldoffCount == 0 && CritSectionCount == 0 && \
-	 QueryCancelHoldoffCount == 0)
+	 QueryCancelHoldoffCount == 0 && CheckingRemoteServersHoldoffCount == 0)
 
 #define HOLD_INTERRUPTS()  (InterruptHoldoffCount++)
 
@@ -152,6 +155,13 @@ do { \
 	CritSectionCount--; \
 } while(0)
 
+#define HOLD_CHECKING_REMOTE_SERVERS_INTERRUPTS()  (CheckingRemoteServersHoldoffCount++)
+
+#define RESUME_CHECKING_REMOTE_SERVERS_INTERRUPTS() \
+do { \
+	Assert(CheckingRemoteServersHoldoffCount > 0); \
+	CheckingRemoteServersHoldoffCount--; \
+} while(0)
 
 /*****************************************************************************
  *	  globals.h --															 *
diff --git a/src/include/utils/timeout.h b/src/include/utils/timeout.h
index 2cbc5de4d9..ceb6b1c12c 100644
--- a/src/include/utils/timeout.h
+++ b/src/include/utils/timeout.h
@@ -34,6 +34,7 @@ typedef enum TimeoutId
 	IDLE_SESSION_TIMEOUT,
 	CLIENT_CONNECTION_CHECK_TIMEOUT,
 	STARTUP_PROGRESS_TIMEOUT,
+	CHECKING_REMOTE_SERVERS_TIMEOUT,
 	/* First user-definable timeout reason */
 	USER_TIMEOUT,
 	/* Maximum number of timeout reasons */