It doesn't violate any rules.. Imagine both the "speaker" and the "text" are being updated by separate threads. A program that would eventually display the behavior in this meme is simple, and I'm a bit embarrassed to have written it because of this comment:
#include <pthread.h>
#include <stdio.h>
char* speakers[] = {
"Alice",
"Bob"
};
int speaker = 0;
void* change_speaker(void* arg)
{
(void)arg;
for (;;) {
speaker = speaker == 0 ? 1 : 0;
}
}
char* texts[] = {
"Hi Bob",
"Hi Alice, what's up?",
"Not much Bob",
};
int text = 0;
void* change_text(void* arg)
{
(void)arg;
for (;;) {
switch (text) {
case 0:
text = 1;
break;
case 1:
text = 2;
break;
case 2:
text = 0;
break;
}
}
}
int main(int argc, char* argv[])
{
pthread_t speaker_swapper, text_swapper;
pthread_create(&text_swapper, NULL, change_text, NULL);
pthread_create(&speaker_swapper, NULL, change_speaker, NULL);
for (int i = 0; i < 3; ++i) {
printf("%s: %s\n", speakers[speaker], texts[text]);
}
}
Yes for example Python implements them using semaphores.