Add missing pthread_barrier_t.

Supply a simple implementation of the missing pthread_barrier_t type and
functions, for macOS.

Discussion: https://postgr.es/m/20200227180100.zyvjwzcpiokfsqm2%40alap3.anarazel.de

src/include/pg_config.h.in

@@ -424,6 +424,9 @@
 /* Define if you have POSIX threads libraries and header files. */
 #undef HAVE_PTHREAD
 
+/* Define to 1 if you have the `pthread_barrier_wait' function. */
+#undef HAVE_PTHREAD_BARRIER_WAIT
+
 /* Define to 1 if you have the `pthread_is_threaded_np' function. */
 #undef HAVE_PTHREAD_IS_THREADED_NP
 

src/include/port/pg_pthread.h

@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * Declarations for missing POSIX thread components.
+ *
+ *	  Currently this supplies an implementation of pthread_barrier_t for the
+ *	  benefit of macOS, which lacks it.  These declarations are not in port.h,
+ *	  because that'd require <pthread.h> to be included by every translation
+ *	  unit.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef PG_PTHREAD_H
+#define PG_PTHREAD_H
+
+#include <pthread.h>
+
+#ifndef HAVE_PTHREAD_BARRIER_WAIT
+
+#ifndef PTHREAD_BARRIER_SERIAL_THREAD
+#define PTHREAD_BARRIER_SERIAL_THREAD (-1)
+#endif
+
+typedef struct pg_pthread_barrier
+{
+	bool		sense;			/* we only need a one bit phase */
+	int			count;			/* number of threads expected */
+	int			arrived;		/* number of threads that have arrived */
+	pthread_mutex_t mutex;
+	pthread_cond_t cond;
+} pthread_barrier_t;
+
+extern int	pthread_barrier_init(pthread_barrier_t *barrier,
+								 const void *attr,
+								 int count);
+extern int	pthread_barrier_wait(pthread_barrier_t *barrier);
+extern int	pthread_barrier_destroy(pthread_barrier_t *barrier);
+
+#endif
+
+#endif

src/port/pthread_barrier_wait.c

@@ -0,0 +1,79 @@
+/*-------------------------------------------------------------------------
+ *
+ * pthread_barrier_wait.c
+ *    Implementation of pthread_barrier_t support for platforms lacking it.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *    src/port/pthread_barrier_wait.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+#include "port/pg_pthread.h"
+
+int
+pthread_barrier_init(pthread_barrier_t *barrier, const void *attr, int count)
+{
+	barrier->sense = false;
+	barrier->count = count;
+	barrier->arrived = 0;
+	if (pthread_cond_init(&barrier->cond, NULL) < 0)
+		return -1;
+	if (pthread_mutex_init(&barrier->mutex, NULL) < 0)
+	{
+		int			save_errno = errno;
+
+		pthread_cond_destroy(&barrier->cond);
+		errno = save_errno;
+
+		return -1;
+	}
+
+	return 0;
+}
+
+int
+pthread_barrier_wait(pthread_barrier_t *barrier)
+{
+	bool		initial_sense;
+
+	pthread_mutex_lock(&barrier->mutex);
+
+	/* We have arrived at the barrier. */
+	barrier->arrived++;
+	Assert(barrier->arrived <= barrier->count);
+
+	/* If we were the last to arrive, release the others and return. */
+	if (barrier->arrived == barrier->count)
+	{
+		barrier->arrived = 0;
+		barrier->sense = !barrier->sense;
+		pthread_mutex_unlock(&barrier->mutex);
+		pthread_cond_broadcast(&barrier->cond);
+
+		return PTHREAD_BARRIER_SERIAL_THREAD;
+	}
+
+	/* Wait for someone else to flip the sense. */
+	initial_sense = barrier->sense;
+	do
+	{
+		pthread_cond_wait(&barrier->cond, &barrier->mutex);
+	} while (barrier->sense == initial_sense);
+
+	pthread_mutex_unlock(&barrier->mutex);
+
+	return 0;
+}
+
+int
+pthread_barrier_destroy(pthread_barrier_t *barrier)
+{
+	pthread_cond_destroy(&barrier->cond);
+	pthread_mutex_destroy(&barrier->mutex);
+	return 0;
+}

src/tools/msvc/Solution.pm

@@ -333,6 +333,7 @@ sub GenerateFiles
 		HAVE_PSTAT                  => undef,
 		HAVE_PS_STRINGS             => undef,
 		HAVE_PTHREAD                => undef,
+		HAVE_PTHREAD_BARRIER_WAIT   => undef,
 		HAVE_PTHREAD_IS_THREADED_NP => undef,
 		HAVE_PTHREAD_PRIO_INHERIT   => undef,
 		HAVE_PWRITE                 => undef,

src/tools/pgindent/typedefs.list

@@ -3295,6 +3295,7 @@ proclist_mutable_iter
 proclist_node
 promptStatus_t
 pthread_attr_t
+pthread_barrier_t
 pthread_key_t
 pthread_mutex_t
 pthread_once_t