Add a test for kernel preemption during a large uiomove.

Per discussion with Jason.

regress/lib/libpthread/preempt1/Makefile

@@ -0,0 +1,16 @@
+#	$NetBSD: Makefile,v 1.1 2003/01/31 20:14:25 skrll Exp $
+
+WARNS=1
+
+PROG=   preempt1
+SRCS=   preempt1.c
+
+LDADD=	-lpthread
+
+NOMAN=
+
+regress:
+	@echo Testing kernel preemption during a large uiomove.
+	./preempt1
+
+.include <bsd.prog.mk>

regress/lib/libpthread/preempt1/preempt1.c

@@ -0,0 +1,89 @@
+/*	$NetBSD: preempt1.c,v 1.1 2003/01/31 20:14:25 skrll Exp $	*/
+
+#include <assert.h>
+#include <err.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+void *threadfunc(void *arg);
+
+pthread_mutex_t mutex;
+pthread_cond_t cond;
+int started;
+
+#define HUGE_BUFFER	1<<20
+#define NTHREADS	1
+
+int
+main(int argc, char *argv[])
+{
+	int ret, i;
+	pthread_t new;
+	void *joinval;
+
+	char *mem;
+	int fd;
+
+	mem = malloc(HUGE_BUFFER);
+	if (mem == NULL)
+		err(1, "malloc");
+
+	fd = open("/dev/urandom", O_RDONLY, 0);
+	if (fd == 0)
+		err(1, "open");
+
+	printf("1: preempt test\n");
+
+	pthread_cond_init(&cond, NULL);
+	pthread_mutex_lock(&mutex);
+
+	started = 0;
+
+	for (i = 0; i < NTHREADS; i++) {
+		ret = pthread_create(&new, NULL, threadfunc, NULL);
+		if (ret != 0)
+			err(1, "pthread_create");
+	}
+
+	while (started < NTHREADS) {
+		pthread_cond_wait(&cond, &mutex);
+	}
+
+	printf("1: Thread has started.\n");
+
+	pthread_mutex_unlock(&mutex);
+	printf("1: After releasing the mutex.\n");
+
+	ret = read(fd, mem, HUGE_BUFFER);
+	close(fd);
+
+	assert(ret == HUGE_BUFFER);
+
+	ret = pthread_join(new, &joinval);
+	if (ret != 0)
+		err(1, "pthread_join");
+
+	printf("1: Thread joined.\n");
+
+	return 0;
+}
+
+void *
+threadfunc(void *arg)
+{
+	printf("2: Second thread.\n");
+
+	printf("2: Locking mutex\n");
+	pthread_mutex_lock(&mutex);
+	printf("2: Got mutex.\n");
+	started++;
+	
+	pthread_mutex_unlock(&mutex);
+	pthread_cond_signal(&cond);
+	sleep(1);
+
+	return NULL;
+}