text: /* Copyright 2016 Google Inc.
  
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License. */
  
  #include "platform.h"
  #include "compiler.h"
  #include "nsync.h"
  #include "time_extra.h"
  #include "smprintf.h"
  #include "testing.h"
  #include "closure.h"
  #include "array.h"
  #include "heap.h"
  
  NSYNC_CPP_USING_
  
  /* Example use of CV.wait():  A priority queue of strings whose
     "remove_with_deadline" operation has a deadline. */
  
  /* --------------------------------------- */
  
  typedef A_TYPE (const char *) a_string; /* An array used as a heap of strings. */
  
  /* heap comparison function */
  static int str_lt (const char *e0, const char *e1) {
  	return (strcmp (e0, e1) < 0);
  }
  
  static void no_set (const char *a UNUSED, int b UNUSED) {
  }
  
  /* --------------------------------------- */
  
  /* A string_priority_queue_cv is a priority queue of strings, which emits the
     lexicographically least string available. */
  typedef struct string_priority_queue_cv_s {
  	nsync_cv non_empty; /* signalled when heap becomes non-empty */
  	nsync_mu mu; /* protects heap */
  	a_string heap;
  } string_priority_queue_cv;
  
  
  /* Add "s" to the queue *q. */
  static void string_priority_queue_cv_add (string_priority_queue_cv *q, const char *s) {
  	int alen;
  	nsync_mu_lock (&q->mu);
  	alen = A_LEN (&q->heap);
  	if (alen == 0) {
  		nsync_cv_broadcast (&q->non_empty);
  	}
  	A_PUSH (&q->heap) = s;
  	heap_add (&A (&q->heap, 0), alen, str_lt, no_set, s);
  	nsync_mu_unlock (&q->mu);
  }
  
  /* Wait until queue *q is non-empty, then remove a string from its
     beginning, and return it; or if abs_deadline is reached before the
     queue becomes non-empty, return NULL. */
  static const char *string_priority_queue_cv_remove_with_deadline (string_priority_queue_cv *q,
  							          nsync_time abs_deadline) {
  	int alen;
  	const char *s = NULL;
  	nsync_mu_lock (&q->mu);
  	while (A_LEN (&q->heap) == 0 &&
  	       nsync_cv_wait_with_deadline (&q->non_empty, &q->mu, abs_deadline, NULL) == 0) {
  	}
  	alen = A_LEN (&q->heap);
  	if (alen != 0) {
  		s = A (&q->heap, 0);
  		heap_remove (&A (&q->heap, 0), alen, str_lt, no_set, 0);
  		A_DISCARD (&q->heap, 1);
  	}
  	nsync_mu_unlock (&q->mu);
  	return (s);
  }
  
  /* Free resources associates with *q */
  static void string_priority_queue_cv_destroy (string_priority_queue_cv *q) {
  	A_FREE (&q->heap);
  }
  
  /* --------------------------------------- */
  
  /* Add strings s[0, ..., n-1] to *q, with the specified delay between additions. */
  static void add_and_wait_cv (string_priority_queue_cv *q, nsync_time delay,
  			     int n, const char *s[]) {
  	int i;
  	for (i = 0; i != n; i++) {
  		string_priority_queue_cv_add (q, s[i]);
  		nsync_time_sleep (delay);
  	}
  }
  
  CLOSURE_DECL_BODY4 (add_and_wait_cv, string_priority_queue_cv *,
  		    nsync_time, int, const char **)
  
  typedef A_TYPE (char) a_char; /* an array or characters */
  
  /* Append the nul-terminated string str[] to *a. */
  static void a_char_append (a_char *a, const char *str) {
  	while (*str != 0) {
  		A_PUSH (a) = *str;
  		str++;
  	}
  }
  
  /* Remove the first item from *q and output it on stdout,
     or output "timeout: <delay>" if no value can be found before "delay" elapses. */
  static void remove_and_print_cv (string_priority_queue_cv *q, nsync_time delay, a_char *output) {
  	const char *s;
  	if ((s = string_priority_queue_cv_remove_with_deadline (
  			q, nsync_time_add (nsync_time_now(), delay))) != NULL) {
  		a_char_append (output, s);
  		a_char_append (output, "\n");
  	} else {
  		char buf[64];
  		snprintf (buf, sizeof (buf), "timeout %gs\n",
  			  nsync_time_to_dbl (delay));
  		a_char_append (output, buf);
  	}
  }
  
  /* Demonstrates the use of nsync_mu_wait() via a priority queue of strings.
     See the routine string_priority_queue_cv_remove_with_deadline(), above. */
  static void example_cv_wait (testing t) {
  	static const char *input[] = { "one", "two", "three", "four", "five" };
  	string_priority_queue_cv q;
  	a_char output;
  	static const char *expected =
  		"one\n"
  		"three\n"
  		"two\n"
  		"timeout 0.1s\n"
  		"four\n"
  		"timeout 0.1s\n"
  		"five\n"
  		"timeout 1s\n";
  
  	memset (&q, 0, sizeof (q));
  	memset (&output, 0, sizeof (output));
  
  	closure_fork (closure_add_and_wait_cv (&add_and_wait_cv, &q,
  					       nsync_time_ms (500), NELEM (input), input));
  
  	/* delay: "one", "two", "three" are queued; not "four" */
  	nsync_time_sleep (nsync_time_ms (1200));
  
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* "one" */
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* "three" (less than "two") */
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* "two" */
  	remove_and_print_cv (&q, nsync_time_ms (100), &output); /* time out because 1.3 < 0.5*3 */
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* "four" */
  	remove_and_print_cv (&q, nsync_time_ms (100), &output); /* time out because 0.1 < 0.5 */
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* "five" */
  	remove_and_print_cv (&q, nsync_time_ms (1000), &output);    /* time out: no more to fetch */
  
  	A_PUSH (&output) = 0;
  	if (strcmp (&A (&output, 0), expected) != 0) {
  		TEST_ERROR (t, ("expected = %s\ngot      = %s\n", expected, &A (&output, 0)));
  	}
  	A_FREE (&output);
  	string_priority_queue_cv_destroy (&q);
  }
  
  int main (int argc, char *argv[]) {
  	testing_base tb = testing_new (argc, argv, 0);
  	TEST_RUN (tb, example_cv_wait);
  	return (testing_base_exit (tb));
  }
  