xtimer_msg_receive_timeout: only send timeout msg if thread still waits for it

[MichelRottleuthner]

Contribution description

This PR fixes #13345 without requiring core_thread_flags.
The idea came from @JulianHolzwarth #13345 (comment)

Testing procedure

In master the following snipped crashes, with this PR it should work.
See #13345 for further details.

#include <stdio.h>
#include <string.h>

#include "xtimer.h"
#include "msg.h"
#include "thread.h"

#define DELAY            (100UL * US_PER_MS)
#define CORRECT_MSG_TYPE (42)
xtimer_t timer;

static void timer_event(void *arg) {
    kernel_pid_t *pid = (kernel_pid_t*)arg;
    msg_t msg = {
        .content.value = 1,
        .type = CORRECT_MSG_TYPE
    };
    puts("Interrupt");
    msg_send_int(&msg, *pid);
    puts("msg send");

    xtimer_set(&timer, DELAY-20);
}

int main(void)
{
    static msg_t rcv_queue[2];
    static msg_t recv;

    printf("You are running RIOT on a(n) %s board.\n", RIOT_BOARD);
    printf("This board features a(n) %s MCU.\n", RIOT_MCU);

    msg_init_queue(rcv_queue, 2);
    timer.callback = timer_event;
    kernel_pid_t pid = thread_getpid();
    timer.arg = (void*)&pid;

    xtimer_set(&timer, DELAY-20);

    while (1) {
        puts("wait");
    	xtimer_msg_receive_timeout(&recv, DELAY);
        puts("received");

        if (recv.type != CORRECT_MSG_TYPE) {
            printf("ERROR received wrong message: %d != %d\n", recv.type,
                   CORRECT_MSG_TYPE);
        }

    	xtimer_sleep(1);
    }
    return 0;
}

Issues/PRs references

Alternative to #13429.

[kaspar030]

This is now racey.

If the thread gets scheduled away after this set(), the timer triggers, then the thread gets scheduled again, it'll sit in msg_receive() forever.

[MichelRottleuthner]

Good catch! Ok how about something like the idea I sketched in #13429 comment then?