Test code for shared memory message queue facility.

This code is intended as a demonstration of how the dynamic shared
memory and dynamic background worker facilities can be used to establish
a group of coooperating processes which can coordinate their activities
using the shared memory message queue facility.  By itself, the code
does nothing particularly interesting: it simply allows messages to
be passed through a loop of workers and back to the original process.
But it's a useful unit test, in addition to its demonstration value.

contrib/test_shm_mq/test_shm_mq.h

@@ -0,0 +1,45 @@
+/*--------------------------------------------------------------------------
+ *
+ * test_shm_mq.h
+ *		Definitions for shared memory message queues
+ *
+ * Copyright (C) 2013, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		contrib/test_shm_mq/test_shm_mq.h
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#ifndef TEST_SHM_MQ_H
+#define TEST_SHM_MQ_H
+
+#include "storage/dsm.h"
+#include "storage/shm_mq.h"
+#include "storage/spin.h"
+
+/* Identifier for shared memory segments used by this extension. */
+#define		PG_TEST_SHM_MQ_MAGIC		0x79fb2447
+
+/*
+ * This structure is stored in the dynamic shared memory segment.  We use
+ * it to determine whether all workers started up OK and successfully
+ * attached to their respective shared message queues.
+ */
+typedef struct
+{
+	slock_t			mutex;
+	int				workers_total;
+	int				workers_attached;
+	int				workers_ready;
+} test_shm_mq_header;
+
+/* Set up dynamic shared memory and background workers for test run. */
+extern void test_shm_mq_setup(uint64 queue_size, int32 nworkers,
+							  dsm_segment **seg, shm_mq_handle **output,
+							  shm_mq_handle **input);
+
+/* Main entrypoint for a worker. */
+extern void	test_shm_mq_main(Datum);
+
+#endif