Refactor query cancellation code into src/fe_utils/

Originally, this code was duplicated in src/bin/psql/ and
src/bin/scripts/, but it can be useful for other frontend applications,
like pgbench.  This refactoring offers the possibility to setup a custom
callback which would get called in the signal handler for SIGINT or when
the interruption console events happen on Windows.

Author: Fabien Coelho, with contributions from Michael Paquier
Reviewed-by: Álvaro Herrera, Ibrar Ahmed
Discussion: https://postgr.es/m/alpine.DEB.2.21.1910311939430.27369@lancre

14 files changed, 294 insertions, 326 deletions

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 0a2597046d..48b6279403 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -29,6 +29,7 @@
 #include "copy.h"
 #include "crosstabview.h"
 #include "describe.h"
+#include "fe_utils/cancel.h"
 #include "fe_utils/print.h"
 #include "fe_utils/string_utils.h"
 #include "help.h"
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index 53a1ea2bdb..9c0d53689e 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -23,6 +23,7 @@
 #include "common/logging.h"
 #include "copy.h"
 #include "crosstabview.h"
+#include "fe_utils/cancel.h"
 #include "fe_utils/mbprint.h"
 #include "fe_utils/string_utils.h"
 #include "portability/instr_time.h"
@@ -228,58 +229,28 @@ NoticeProcessor(void *arg, const char *message)
  * Code to support query cancellation
  *
  * Before we start a query, we enable the SIGINT signal catcher to send a
- * cancel request to the backend. Note that sending the cancel directly from
- * the signal handler is safe because PQcancel() is written to make it
- * so. We use write() to report to stderr because it's better to use simple
- * facilities in a signal handler.
- *
- * On win32, the signal canceling happens on a separate thread, because
- * that's how SetConsoleCtrlHandler works. The PQcancel function is safe
- * for this (unlike PQrequestCancel). However, a CRITICAL_SECTION is required
- * to protect the PGcancel structure against being changed while the signal
- * thread is using it.
+ * cancel request to the backend.
  *
  * SIGINT is supposed to abort all long-running psql operations, not only
  * database queries.  In most places, this is accomplished by checking
- * cancel_pressed during long-running loops.  However, that won't work when
+ * CancelRequested during long-running loops.  However, that won't work when
  * blocked on user input (in readline() or fgets()).  In those places, we
  * set sigint_interrupt_enabled true while blocked, instructing the signal
  * catcher to longjmp through sigint_interrupt_jmp.  We assume readline and
- * fgets are coded to handle possible interruption.  (XXX currently this does
- * not work on win32, so control-C is less useful there)
+ * fgets are coded to handle possible interruption.
+ *
+ * On Windows, currently this does not work, so control-C is less useful
+ * there, and the callback is just a no-op.
  */
 volatile bool sigint_interrupt_enabled = false;
 
 sigjmp_buf	sigint_interrupt_jmp;
 
-static PGcancel *volatile cancelConn = NULL;
-
-#ifdef WIN32
-static CRITICAL_SECTION cancelConnLock;
-#endif
-
-/*
- * Write a simple string to stderr --- must be safe in a signal handler.
- * We ignore the write() result since there's not much we could do about it.
- * Certain compilers make that harder than it ought to be.
- */
-#define write_stderr(str) \
-	do { \
-		const char *str_ = (str); \
-		int		rc_; \
-		rc_ = write(fileno(stderr), str_, strlen(str_)); \
-		(void) rc_; \
-	} while (0)
-
-
 #ifndef WIN32
 
 static void
-handle_sigint(SIGNAL_ARGS)
+psql_cancel_callback(void)
 {
-	int			save_errno = errno;
-	char		errbuf[256];
-
 	/* if we are waiting for input, longjmp out of it */
 	if (sigint_interrupt_enabled)
 	{
@@ -288,74 +259,24 @@ handle_sigint(SIGNAL_ARGS)
 	}
 
 	/* else, set cancel flag to stop any long-running loops */
-	cancel_pressed = true;
-
-	/* and send QueryCancel if we are processing a database query */
-	if (cancelConn != NULL)
-	{
-		if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
-			write_stderr("Cancel request sent\n");
-		else
-		{
-			write_stderr("Could not send cancel request: ");
-			write_stderr(errbuf);
-		}
-	}
-
-	errno = save_errno;			/* just in case the write changed it */
+	CancelRequested = true;
 }
 
-void
-setup_cancel_handler(void)
-{
-	pqsignal(SIGINT, handle_sigint);
-}
-#else							/* WIN32 */
+#else
 
-static BOOL WINAPI
-consoleHandler(DWORD dwCtrlType)
+static void
+psql_cancel_callback(void)
 {
-	char		errbuf[256];
-
-	if (dwCtrlType == CTRL_C_EVENT ||
-		dwCtrlType == CTRL_BREAK_EVENT)
-	{
-		/*
-		 * Can't longjmp here, because we are in wrong thread :-(
-		 */
-
-		/* set cancel flag to stop any long-running loops */
-		cancel_pressed = true;
-
-		/* and send QueryCancel if we are processing a database query */
-		EnterCriticalSection(&cancelConnLock);
-		if (cancelConn != NULL)
-		{
-			if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
-				write_stderr("Cancel request sent\n");
-			else
-			{
-				write_stderr("Could not send cancel request: ");
-				write_stderr(errbuf);
-			}
-		}
-		LeaveCriticalSection(&cancelConnLock);
-
-		return TRUE;
-	}
-	else
-		/* Return FALSE for any signals not being handled */
-		return FALSE;
+	/* nothing to do here */
 }
 
+#endif							/* !WIN32 */
+
 void
-setup_cancel_handler(void)
+psql_setup_cancel_handler(void)
 {
-	InitializeCriticalSection(&cancelConnLock);
-
-	SetConsoleCtrlHandler(consoleHandler, TRUE);
+	setup_cancel_handler(psql_cancel_callback);
 }
-#endif							/* WIN32 */
 
 
 /* ConnectionUp
@@ -428,62 +349,6 @@ CheckConnection(void)
 
 
 
-/*
- * SetCancelConn
- *
- * Set cancelConn to point to the current database connection.
- */
-void
-SetCancelConn(void)
-{
-	PGcancel   *oldCancelConn;
-
-#ifdef WIN32
-	EnterCriticalSection(&cancelConnLock);
-#endif
-
-	/* Free the old one if we have one */
-	oldCancelConn = cancelConn;
-	/* be sure handle_sigint doesn't use pointer while freeing */
-	cancelConn = NULL;
-
-	if (oldCancelConn != NULL)
-		PQfreeCancel(oldCancelConn);
-
-	cancelConn = PQgetCancel(pset.db);
-
-#ifdef WIN32
-	LeaveCriticalSection(&cancelConnLock);
-#endif
-}
-
-
-/*
- * ResetCancelConn
- *
- * Free the current cancel connection, if any, and set to NULL.
- */
-void
-ResetCancelConn(void)
-{
-	PGcancel   *oldCancelConn;
-
-#ifdef WIN32
-	EnterCriticalSection(&cancelConnLock);
-#endif
-
-	oldCancelConn = cancelConn;
-	/* be sure handle_sigint doesn't use pointer while freeing */
-	cancelConn = NULL;
-
-	if (oldCancelConn != NULL)
-		PQfreeCancel(oldCancelConn);
-
-#ifdef WIN32
-	LeaveCriticalSection(&cancelConnLock);
-#endif
-}
-
 
 /*
  * AcceptResult
@@ -707,7 +572,7 @@ PSQLexec(const char *query)
 			return NULL;
 	}
 
-	SetCancelConn();
+	SetCancelConn(pset.db);
 
 	res = PQexec(pset.db, query);
 
@@ -746,7 +611,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt)
 		return 0;
 	}
 
-	SetCancelConn();
+	SetCancelConn(pset.db);
 
 	if (pset.timing)
 		INSTR_TIME_SET_CURRENT(before);
@@ -773,7 +638,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt)
 	 * consumed.  The user's intention, though, is to cancel the entire watch
 	 * process, so detect a sent cancellation request and exit in this case.
 	 */
-	if (cancel_pressed)
+	if (CancelRequested)
 	{
 		PQclear(res);
 		return 0;
@@ -973,8 +838,8 @@ ExecQueryTuples(const PGresult *result)
 			{
 				const char *query = PQgetvalue(result, r, c);
 
-				/* Abandon execution if cancel_pressed */
-				if (cancel_pressed)
+				/* Abandon execution if CancelRequested */
+				if (CancelRequested)
 					goto loop_exit;
 
 				/*
@@ -1091,7 +956,7 @@ ProcessResult(PGresult **results)
 			FILE	   *copystream;
 			PGresult   *copy_result;
 
-			SetCancelConn();
+			SetCancelConn(pset.db);
 			if (result_status == PGRES_COPY_OUT)
 			{
 				bool		need_close = false;
@@ -1342,7 +1207,7 @@ SendQuery(const char *query)
 		if (fgets(buf, sizeof(buf), stdin) != NULL)
 			if (buf[0] == 'x')
 				goto sendquery_cleanup;
-		if (cancel_pressed)
+		if (CancelRequested)
 			goto sendquery_cleanup;
 	}
 	else if (pset.echo == PSQL_ECHO_QUERIES)
@@ -1360,7 +1225,7 @@ SendQuery(const char *query)
 		fflush(pset.logfile);
 	}
 
-	SetCancelConn();
+	SetCancelConn(pset.db);
 
 	transaction_status = PQtransactionStatus(pset.db);
 
@@ -1886,7 +1751,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 		 * writing things to the stream, we presume $PAGER has disappeared and
 		 * stop bothering to pull down more data.
 		 */
-		if (ntuples < fetch_count || cancel_pressed || flush_error ||
+		if (ntuples < fetch_count || CancelRequested || flush_error ||
 			ferror(fout))
 			break;
 	}
diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h
index 292dc54919..60ff9f1758 100644
--- a/src/bin/psql/common.h
+++ b/src/bin/psql/common.h
@@ -26,10 +26,7 @@ extern volatile bool sigint_interrupt_enabled;
 
 extern sigjmp_buf sigint_interrupt_jmp;
 
-extern void setup_cancel_handler(void);
-
-extern void SetCancelConn(void);
-extern void ResetCancelConn(void);
+extern void psql_setup_cancel_handler(void);
 
 extern PGresult *PSQLexec(const char *query);
 extern int	PSQLexecWatch(const char *query, const printQueryOpt *opt);
diff --git a/src/bin/psql/large_obj.c b/src/bin/psql/large_obj.c
index 042403e0f7..75b733c3c8 100644
--- a/src/bin/psql/large_obj.c
+++ b/src/bin/psql/large_obj.c
@@ -9,6 +9,7 @@
 
 #include "common.h"
 #include "common/logging.h"
+#include "fe_utils/cancel.h"
 #include "large_obj.h"
 #include "settings.h"
 
@@ -146,7 +147,7 @@ do_lo_export(const char *loid_arg, const char *filename_arg)
 	if (!start_lo_xact("\\lo_export", &own_transaction))
 		return false;
 
-	SetCancelConn();
+	SetCancelConn(NULL);
 	status = lo_export(pset.db, atooid(loid_arg), filename_arg);
 	ResetCancelConn();
 
@@ -182,7 +183,7 @@ do_lo_import(const char *filename_arg, const char *comment_arg)
 	if (!start_lo_xact("\\lo_import", &own_transaction))
 		return false;
 
-	SetCancelConn();
+	SetCancelConn(NULL);
 	loid = lo_import(pset.db, filename_arg);
 	ResetCancelConn();
 
@@ -244,7 +245,7 @@ do_lo_unlink(const char *loid_arg)
 	if (!start_lo_xact("\\lo_unlink", &own_transaction))
 		return false;
 
-	SetCancelConn();
+	SetCancelConn(NULL);
 	status = lo_unlink(pset.db, loid);
 	ResetCancelConn();
 
diff --git a/src/bin/psql/startup.c b/src/bin/psql/startup.c
index 0d941ef5ba..43cf139a31 100644
--- a/src/bin/psql/startup.c
+++ b/src/bin/psql/startup.c
@@ -301,7 +301,7 @@ main(int argc, char *argv[])
 		exit(EXIT_BADCONN);
 	}
 
-	setup_cancel_handler();
+	psql_setup_cancel_handler();
 
 	PQsetNoticeProcessor(pset.db, NoticeProcessor, NULL);
 
diff --git a/src/bin/scripts/clusterdb.c b/src/bin/scripts/clusterdb.c
index d380127356..3aee5f2834 100644
--- a/src/bin/scripts/clusterdb.c
+++ b/src/bin/scripts/clusterdb.c
@@ -133,7 +133,7 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
-	setup_cancel_handler();
+	setup_cancel_handler(NULL);
 
 	if (alldb)
 	{
diff --git a/src/bin/scripts/common.c b/src/bin/scripts/common.c
index 1b38a1da49..d2a7547441 100644
--- a/src/bin/scripts/common.c
+++ b/src/bin/scripts/common.c
@@ -24,14 +24,6 @@
 
 #define ERRCODE_UNDEFINED_TABLE  "42P01"
 
-
-static PGcancel *volatile cancelConn = NULL;
-bool		CancelRequested = false;
-
-#ifdef WIN32
-static CRITICAL_SECTION cancelConnLock;
-#endif
-
 /*
  * Provide strictly harmonized handling of --help and --version
  * options.
@@ -465,142 +457,3 @@ yesno_prompt(const char *question)
 			   _(PG_YESLETTER), _(PG_NOLETTER));
 	}
 }
-
-/*
- * SetCancelConn
- *
- * Set cancelConn to point to the current database connection.
- */
-void
-SetCancelConn(PGconn *conn)
-{
-	PGcancel   *oldCancelConn;
-
-#ifdef WIN32
-	EnterCriticalSection(&cancelConnLock);
-#endif
-
-	/* Free the old one if we have one */
-	oldCancelConn = cancelConn;
-
-	/* be sure handle_sigint doesn't use pointer while freeing */
-	cancelConn = NULL;
-
-	if (oldCancelConn != NULL)
-		PQfreeCancel(oldCancelConn);
-
-	cancelConn = PQgetCancel(conn);
-
-#ifdef WIN32
-	LeaveCriticalSection(&cancelConnLock);
-#endif
-}
-
-/*
- * ResetCancelConn
- *
- * Free the current cancel connection, if any, and set to NULL.
- */
-void
-ResetCancelConn(void)
-{
-	PGcancel   *oldCancelConn;
-
-#ifdef WIN32
-	EnterCriticalSection(&cancelConnLock);
-#endif
-
-	oldCancelConn = cancelConn;
-
-	/* be sure handle_sigint doesn't use pointer while freeing */
-	cancelConn = NULL;
-
-	if (oldCancelConn != NULL)
-		PQfreeCancel(oldCancelConn);
-
-#ifdef WIN32
-	LeaveCriticalSection(&cancelConnLock);
-#endif
-}
-
-#ifndef WIN32
-/*
- * Handle interrupt signals by canceling the current command, if a cancelConn
- * is set.
- */
-static void
-handle_sigint(SIGNAL_ARGS)
-{
-	int			save_errno = errno;
-	char		errbuf[256];
-
-	/* Send QueryCancel if we are processing a database query */
-	if (cancelConn != NULL)
-	{
-		if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
-		{
-			CancelRequested = true;
-			fprintf(stderr, _("Cancel request sent\n"));
-		}
-		else
-			fprintf(stderr, _("Could not send cancel request: %s"), errbuf);
-	}
-	else
-		CancelRequested = true;
-
-	errno = save_errno;			/* just in case the write changed it */
-}
-
-void
-setup_cancel_handler(void)
-{
-	pqsignal(SIGINT, handle_sigint);
-}
-#else							/* WIN32 */
-
-/*
- * Console control handler for Win32. Note that the control handler will
- * execute on a *different thread* than the main one, so we need to do
- * proper locking around those structures.
- */
-static BOOL WINAPI
-consoleHandler(DWORD dwCtrlType)
-{
-	char		errbuf[256];
-
-	if (dwCtrlType == CTRL_C_EVENT ||
-		dwCtrlType == CTRL_BREAK_EVENT)
-	{
-		/* Send QueryCancel if we are processing a database query */
-		EnterCriticalSection(&cancelConnLock);
-		if (cancelConn != NULL)
-		{
-			if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
-			{
-				fprintf(stderr, _("Cancel request sent\n"));
-				CancelRequested = true;
-			}
-			else
-				fprintf(stderr, _("Could not send cancel request: %s"), errbuf);
-		}
-		else
-			CancelRequested = true;
-
-		LeaveCriticalSection(&cancelConnLock);
-
-		return TRUE;
-	}
-	else
-		/* Return FALSE for any signals not being handled */
-		return FALSE;
-}
-
-void
-setup_cancel_handler(void)
-{
-	InitializeCriticalSection(&cancelConnLock);
-
-	SetConsoleCtrlHandler(consoleHandler, TRUE);
-}
-
-#endif							/* WIN32 */
diff --git a/src/bin/scripts/common.h b/src/bin/scripts/common.h
index b8580f927a..db2f85b472 100644
--- a/src/bin/scripts/common.h
+++ b/src/bin/scripts/common.h
@@ -10,6 +10,7 @@
 #define COMMON_H
 
 #include "common/username.h"
+#include "fe_utils/cancel.h"
 #include "getopt_long.h"		/* pgrminclude ignore */
 #include "libpq-fe.h"
 #include "pqexpbuffer.h"		/* pgrminclude ignore */
@@ -60,10 +61,4 @@ extern void appendQualifiedRelation(PQExpBuffer buf, const char *name,
 
 extern bool yesno_prompt(const char *question);
 
-extern void setup_cancel_handler(void);
-
-extern void SetCancelConn(PGconn *conn);
-extern void ResetCancelConn(void);
-
-
 #endif							/* COMMON_H */
diff --git a/src/bin/scripts/reindexdb.c b/src/bin/scripts/reindexdb.c
index f00aec15de..bedd95cf9d 100644
--- a/src/bin/scripts/reindexdb.c
+++ b/src/bin/scripts/reindexdb.c
@@ -187,7 +187,7 @@ main(int argc, char *argv[])
 		exit(1);
 	}
 
-	setup_cancel_handler();
+	setup_cancel_handler(NULL);
 
 	if (alldb)
 	{
diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c
index 2c7219239f..83a94dc632 100644
--- a/src/bin/scripts/vacuumdb.c
+++ b/src/bin/scripts/vacuumdb.c
@@ -257,7 +257,7 @@ main(int argc, char *argv[])
 		/* allow 'and_analyze' with 'analyze_only' */
 	}
 
-	setup_cancel_handler();
+	setup_cancel_handler(NULL);
 
 	/* Avoid opening extra connections. */
 	if (tbl_count && (concurrentCons > tbl_count))
diff --git a/src/fe_utils/Makefile b/src/fe_utils/Makefile
index beea506536..e029333194 100644
--- a/src/fe_utils/Makefile
+++ b/src/fe_utils/Makefile
@@ -20,6 +20,7 @@ include $(top_builddir)/src/Makefile.global
 override CPPFLAGS := -DFRONTEND -I$(libpq_srcdir) $(CPPFLAGS)
 
 OBJS = \
+	cancel.o \
 	conditional.o \
 	mbprint.o \
 	print.o \
diff --git a/src/fe_utils/cancel.c b/src/fe_utils/cancel.c
new file mode 100644
index 0000000000..04e0d1e3b2
--- /dev/null
+++ b/src/fe_utils/cancel.c
@@ -0,0 +1,225 @@
+/*------------------------------------------------------------------------
+ *
+ * Query cancellation support for frontend code
+ *
+ * Assorted utility functions to control query cancellation with signal
+ * handler for SIGINT.
+ *
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/fe-utils/cancel.c
+ *
+ *------------------------------------------------------------------------
+ */
+
+#include "postgres_fe.h"
+
+#include <signal.h>
+#include <unistd.h>
+
+#include "fe_utils/cancel.h"
+#include "fe_utils/connect.h"
+#include "fe_utils/string_utils.h"
+
+
+/*
+ * Write a simple string to stderr --- must be safe in a signal handler.
+ * We ignore the write() result since there's not much we could do about it.
+ * Certain compilers make that harder than it ought to be.
+ */
+#define write_stderr(str) \
+	do { \
+		const char *str_ = (str); \
+		int		rc_; \
+		rc_ = write(fileno(stderr), str_, strlen(str_)); \
+		(void) rc_; \
+	} while (0)
+
+static PGcancel *volatile cancelConn = NULL;
+bool		CancelRequested = false;
+
+#ifdef WIN32
+static CRITICAL_SECTION cancelConnLock;
+#endif
+
+/*
+ * Additional callback for cancellations.
+ */
+static void (*cancel_callback) (void) = NULL;
+
+
+/*
+ * SetCancelConn
+ *
+ * Set cancelConn to point to the current database connection.
+ */
+void
+SetCancelConn(PGconn *conn)
+{
+	PGcancel   *oldCancelConn;
+
+#ifdef WIN32
+	EnterCriticalSection(&cancelConnLock);
+#endif
+
+	/* Free the old one if we have one */
+	oldCancelConn = cancelConn;
+
+	/* be sure handle_sigint doesn't use pointer while freeing */
+	cancelConn = NULL;
+
+	if (oldCancelConn != NULL)
+		PQfreeCancel(oldCancelConn);
+
+	cancelConn = PQgetCancel(conn);
+
+#ifdef WIN32
+	LeaveCriticalSection(&cancelConnLock);
+#endif
+}
+
+/*
+ * ResetCancelConn
+ *
+ * Free the current cancel connection, if any, and set to NULL.
+ */
+void
+ResetCancelConn(void)
+{
+	PGcancel   *oldCancelConn;
+
+#ifdef WIN32
+	EnterCriticalSection(&cancelConnLock);
+#endif
+
+	oldCancelConn = cancelConn;
+
+	/* be sure handle_sigint doesn't use pointer while freeing */
+	cancelConn = NULL;
+
+	if (oldCancelConn != NULL)
+		PQfreeCancel(oldCancelConn);
+
+#ifdef WIN32
+	LeaveCriticalSection(&cancelConnLock);
+#endif
+}
+
+
+/*
+ * Code to support query cancellation
+ *
+ * Note that sending the cancel directly from the signal handler is safe
+ * because PQcancel() is written to make it so.  We use write() to report
+ * to stderr because it's better to use simple facilities in a signal
+ * handler.
+ *
+ * On Windows, the signal canceling happens on a separate thread, because
+ * that's how SetConsoleCtrlHandler works.  The PQcancel function is safe
+ * for this (unlike PQrequestCancel).  However, a CRITICAL_SECTION is required
+ * to protect the PGcancel structure against being changed while the signal
+ * thread is using it.
+ */
+
+#ifndef WIN32
+
+/*
+ * handle_sigint
+ *
+ * Handle interrupt signals by canceling the current command, if cancelConn
+ * is set.
+ */
+static void
+handle_sigint(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+	char		errbuf[256];
+
+	if (cancel_callback != NULL)
+		cancel_callback();
+
+	/* Send QueryCancel if we are processing a database query */
+	if (cancelConn != NULL)
+	{
+		if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
+		{
+			CancelRequested = true;
+			write_stderr(_("Cancel request sent\n"));
+		}
+		else
+		{
+			write_stderr(_("Could not send cancel request: "));
+			write_stderr(errbuf);
+		}
+	}
+	else
+		CancelRequested = true;
+
+	errno = save_errno;			/* just in case the write changed it */
+}
+
+/*
+ * setup_cancel_handler
+ *
+ * Register query cancellation callback for SIGINT.
+ */
+void
+setup_cancel_handler(void (*callback) (void))
+{
+	cancel_callback = callback;
+	pqsignal(SIGINT, handle_sigint);
+}
+
+#else							/* WIN32 */
+
+static BOOL WINAPI
+consoleHandler(DWORD dwCtrlType)
+{
+	char		errbuf[256];
+
+	if (dwCtrlType == CTRL_C_EVENT ||
+		dwCtrlType == CTRL_BREAK_EVENT)
+	{
+		if (cancel_callback != NULL)
+			cancel_callback();
+
+		/* Send QueryCancel if we are processing a database query */
+		EnterCriticalSection(&cancelConnLock);
+		if (cancelConn != NULL)
+		{
+			if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
+			{
+				write_stderr(_("Cancel request sent\n"));
+				CancelRequested = true;
+			}
+			else
+			{
+				write_stderr(_("Could not send cancel request: %s"));
+				write_stderr(errbuf);
+			}
+		}
+		else
+			CancelRequested = true;
+
+		LeaveCriticalSection(&cancelConnLock);
+
+		return TRUE;
+	}
+	else
+		/* Return FALSE for any signals not being handled */
+		return FALSE;
+}
+
+void
+setup_cancel_handler(void (*callback) (void))
+{
+	cancel_callback = callback;
+
+	InitializeCriticalSection(&cancelConnLock);
+
+	SetConsoleCtrlHandler(consoleHandler, TRUE);
+}
+
+#endif							/* WIN32 */
diff --git a/src/include/fe_utils/cancel.h b/src/include/fe_utils/cancel.h
new file mode 100644
index 0000000000..959a38acf3
--- /dev/null
+++ b/src/include/fe_utils/cancel.h
@@ -0,0 +1,30 @@
+/*-------------------------------------------------------------------------
+ *
+ * Query cancellation support for frontend code
+ *
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/fe_utils/cancel.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef CANCEL_H
+#define CANCEL_H
+
+#include "libpq-fe.h"
+
+extern bool CancelRequested;
+
+extern void SetCancelConn(PGconn *conn);
+extern void ResetCancelConn(void);
+
+/*
+ * A callback can be optionally set up to be called at cancellation
+ * time.
+ */
+extern void setup_cancel_handler(void (*cancel_callback) (void));
+
+#endif							/* CANCEL_H */
diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index 9a0963a050..afa29b5ff8 100644
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -142,7 +142,7 @@ sub mkvcbuild
 	our @pgcommonbkndfiles = @pgcommonallfiles;
 
 	our @pgfeutilsfiles = qw(
-	  conditional.c mbprint.c print.c psqlscan.l psqlscan.c
+	  cancel.c conditional.c mbprint.c print.c psqlscan.l psqlscan.c
 	  simple_list.c string_utils.c recovery_gen.c);
 
 	$libpgport = $solution->AddProject('libpgport', 'lib', 'misc');