1.. _samples_kernel_simple_condition_variables:
2
3Condition Variables
4###################
5
6Overview
7********
8
9This sample demonstrates the usage of condition variables in a
10multithreaded application. Condition variables are used with a mutex
11to signal changing states (conditions) from worker thread to the main
12thread. Main thread uses a condition variable to wait for a condition to
13become true. Main thread and the worker thread alternate between their
14execution based on when the worker thread signals the main thread that is
15pending on the condition variable. The sample can be used with any
16:ref:`supported board <boards>` and prints the sample output shown to
17the console.
18
19Building and Running
20********************
21
22This application can be built and executed on :ref:`native_sim <native_sim>` as follows:
23
24.. zephyr-app-commands::
25   :zephyr-app: samples/kernel/condition_variables/simple
26   :host-os: unix
27   :board: native_sim
28   :goals: run
29   :compact:
30
31To build for another board, change ``native_sim`` above to that board's name.
32
33Sample Output
34=============
35
36.. code-block:: console
37
38    [thread 0] working (0/5)
39    [thread 1] working (0/5)
40    [thread 2] working (0/5)
41    [thread 3] working (0/5)
42    [thread 4] working (0/5)
43    [thread 5] working (0/5)
44    [thread 6] working (0/5)
45    [thread 7] working (0/5)
46    [thread 8] working (0/5)
47    [thread 9] working (0/5)
48    [thread 10] working (0/5)
49    [thread 11] working (0/5)
50    [thread 12] working (0/5)
51    [thread 13] working (0/5)
52    [thread 14] working (0/5)
53    [thread 15] working (0/5)
54    [thread 16] working (0/5)
55    [thread 17] working (0/5)
56    [thread 18] working (0/5)
57    [thread 19] working (0/5)
58    [thread 0] working (1/5)
59    [thread 1] working (1/5)
60    [thread 2] working (1/5)
61    [thread 3] working (1/5)
62    [thread 4] working (1/5)
63    [thread 5] working (1/5)
64    [thread 6] working (1/5)
65    [thread 7] working (1/5)
66    [thread 8] working (1/5)
67    [thread 9] working (1/5)
68    [thread 10] working (1/5)
69    [thread 11] working (1/5)
70    [thread 12] working (1/5)
71    [thread 13] working (1/5)
72    [thread 14] working (1/5)
73    [thread 15] working (1/5)
74    [thread 16] working (1/5)
75    [thread 17] working (1/5)
76    [thread 18] working (1/5)
77    [thread 19] working (1/5)
78    [thread zephyr_app_main] done is 0 which is < 20 so waiting on cond
79    [thread 0] working (2/5)
80    [thread 1] working (2/5)
81    [thread 2] working (2/5)
82    [thread 3] working (2/5)
83    [thread 4] working (2/5)
84    [thread 5] working (2/5)
85    [thread 6] working (2/5)
86    [thread 7] working (2/5)
87    [thread 8] working (2/5)
88    [thread 9] working (2/5)
89    [thread 10] working (2/5)
90    [thread 11] working (2/5)
91    [thread 12] working (2/5)
92    [thread 13] working (2/5)
93    [thread 14] working (2/5)
94    [thread 15] working (2/5)
95    [thread 16] working (2/5)
96    [thread 17] working (2/5)
97    [thread 18] working (2/5)
98    [thread 19] working (2/5)
99    [thread 0] working (3/5)
100    [thread 1] working (3/5)
101    [thread 2] working (3/5)
102    [thread 3] working (3/5)
103    [thread 4] working (3/5)
104    [thread 5] working (3/5)
105    [thread 6] working (3/5)
106    [thread 7] working (3/5)
107    [thread 8] working (3/5)
108    [thread 9] working (3/5)
109    [thread 10] working (3/5)
110    [thread 11] working (3/5)
111    [thread 12] working (3/5)
112    [thread 13] working (3/5)
113    [thread 14] working (3/5)
114    [thread 15] working (3/5)
115    [thread 16] working (3/5)
116    [thread 17] working (3/5)
117    [thread 18] working (3/5)
118    [thread 19] working (3/5)
119    [thread 0] working (4/5)
120    [thread 1] working (4/5)
121    [thread 2] working (4/5)
122    [thread 3] working (4/5)
123    [thread 4] working (4/5)
124    [thread 5] working (4/5)
125    [thread 6] working (4/5)
126    [thread 7] working (4/5)
127    [thread 8] working (4/5)
128    [thread 9] working (4/5)
129    [thread 10] working (4/5)
130    [thread 11] working (4/5)
131    [thread 12] working (4/5)
132    [thread 13] working (4/5)
133    [thread 14] working (4/5)
134    [thread 15] working (4/5)
135    [thread 16] working (4/5)
136    [thread 17] working (4/5)
137    [thread 18] working (4/5)
138    [thread 19] working (4/5)
139    [thread 0] done is now 1. Signalling cond.
140    [thread zephyr_app_main] wake - cond was signalled.
141    [thread zephyr_app_main] done is 1 which is < 20 so waiting on cond
142    [thread 1] done is now 2. Signalling cond.
143    [thread zephyr_app_main] wake - cond was signalled.
144    [thread zephyr_app_main] done is 2 which is < 20 so waiting on cond
145    [thread 2] done is now 3. Signalling cond.
146    [thread zephyr_app_main] wake - cond was signalled.
147    [thread zephyr_app_main] done is 3 which is < 20 so waiting on cond
148    [thread 3] done is now 4. Signalling cond.
149    [thread zephyr_app_main] wake - cond was signalled.
150    [thread zephyr_app_main] done is 4 which is < 20 so waiting on cond
151    [thread 4] done is now 5. Signalling cond.
152    [thread zephyr_app_main] wake - cond was signalled.
153    [thread zephyr_app_main] done is 5 which is < 20 so waiting on cond
154    [thread 5] done is now 6. Signalling cond.
155    [thread zephyr_app_main] wake - cond was signalled.
156    [thread zephyr_app_main] done is 6 which is < 20 so waiting on cond
157    [thread 6] done is now 7. Signalling cond.
158    [thread zephyr_app_main] wake - cond was signalled.
159    [thread zephyr_app_main] done is 7 which is < 20 so waiting on cond
160    [thread 7] done is now 8. Signalling cond.
161    [thread zephyr_app_main] wake - cond was signalled.
162    [thread zephyr_app_main] done is 8 which is < 20 so waiting on cond
163    [thread 8] done is now 9. Signalling cond.
164    [thread zephyr_app_main] wake - cond was signalled.
165    [thread zephyr_app_main] done is 9 which is < 20 so waiting on cond
166    [thread 9] done is now 10. Signalling cond.
167    [thread zephyr_app_main] wake - cond was signalled.
168    [thread zephyr_app_main] done is 10 which is < 20 so waiting on cond
169    [thread 10] done is now 11. Signalling cond.
170    [thread zephyr_app_main] wake - cond was signalled.
171    [thread zephyr_app_main] done is 11 which is < 20 so waiting on cond
172    [thread 11] done is now 12. Signalling cond.
173    [thread zephyr_app_main] wake - cond was signalled.
174    [thread zephyr_app_main] done is 12 which is < 20 so waiting on cond
175    [thread 12] done is now 13. Signalling cond.
176    [thread zephyr_app_main] wake - cond was signalled.
177    [thread zephyr_app_main] done is 13 which is < 20 so waiting on cond
178    [thread 13] done is now 14. Signalling cond.
179    [thread zephyr_app_main] wake - cond was signalled.
180    [thread zephyr_app_main] done is 14 which is < 20 so waiting on cond
181    [thread 14] done is now 15. Signalling cond.
182    [thread zephyr_app_main] wake - cond was signalled.
183    [thread zephyr_app_main] done is 15 which is < 20 so waiting on cond
184    [thread 15] done is now 16. Signalling cond.
185    [thread zephyr_app_main] wake - cond was signalled.
186    [thread zephyr_app_main] done is 16 which is < 20 so waiting on cond
187    [thread 16] done is now 17. Signalling cond.
188    [thread zephyr_app_main] wake - cond was signalled.
189    [thread zephyr_app_main] done is 17 which is < 20 so waiting on cond
190    [thread 17] done is now 18. Signalling cond.
191    [thread zephyr_app_main] wake - cond was signalled.
192    [thread zephyr_app_main] done is 18 which is < 20 so waiting on cond
193    [thread 18] done is now 19. Signalling cond.
194    [thread zephyr_app_main] wake - cond was signalled.
195    [thread zephyr_app_main] done is 19 which is < 20 so waiting on cond
196    [thread 19] done is now 20. Signalling cond.
197    [thread zephyr_app_main] wake - cond was signalled.
198    [thread zephyr_app_main] done == 20 so everyone is done
199