FreeRTOS task mutually exclusive execution - c++

Question

I have a FreeRTOS task generator_task that generates random number once a second and stores it in buffer (this is int32_t for simplifying).
Some of generated values are magic, some are not. Task generator_task can not check if generated value is magic (requirement by design).
I have two equal FreeRTOS tasks magic_printer_task that detect button press, calls int32_t get_magic_value() and prints ButtonX pressed, magic value is %d. Function get_magic_value() must be blocking and very simple to use.
Function get_magic_value() is allowed to check if value is magic or not. Function get_magic_value() from specific task is required (by design) to monopolize reading values generated by generator_task until it gets value that treated as magic. From start and until generator_task generates magic value, get_magic_value from (example)task1 must not allow any other task to read generated values. So, other tasks should wait until task1 will get a magic value. If get_magic_value() reads non-magic value, it continues to monopolize generator and waits for next value.
Question is: How should I swap running-blocked states between two specific tasks, not giving other tasks to intercept control over those two specific tasks?
Could you help me to write lines marked with // =>>> to achieve my goals?
FreeRTOS-like C Pseudo Code:
int32_t buffer;
SemaphoreHandle_t buffer_lock;
SemaphoreHandle_t generator_attachment_lock;
bool result_accepted;
void generator_task(void* pvParams)
{
for(;;)
{
xSemaphoreTake(buffer_lock, portMAX_DELAY);
buffer = random(); buffer *= 2; buffer += random();
result_accepted = false;
// =>>> Check if some task locked generator_attachment_lock
// =>>> Give control to task who locked generator_attachment_lock
// =>>> Suspend until task who locked generator_attachment_lock wakes me
if (!result_accepted) {printf("Not accepted: %d", buffer);}
xSemaphoreGive(buffer_lock);
vTaskDelay(1000);
}
}
int32_t get_magic_value()
{
int32_t value;
xSemaphoreTake(generator_attachment_lock, portMAX_DELAY);
bool is_value_magic = false;
do {
// =>>> Suspend until generator_task wakes me
value = get_generator_value();
is_value_magic = value_is_magic(value);
result_accepted = is_value_magic;
// =>>> Wake generator_task
} while (!is_value_magic);
xSemaphoreGive(generator_attachment_lock);
return value;
}
int32_t get_generator_value()
{
int32_t value;
xSemaphoreTake(buffer_lock, portMAX_DELAY);
value = buffer;
xSemaphoreGive(buffer_lock);
return value;
}
void magic_printer_task(void* pvParams)
{
char * btnName = (char*)pvParams;
for(;;)
{
if (button_pressed(btnName)) { printf("%s magic value: %d", btnName, get_magic_value());}
vTaskDelay(50);
}
}
void main()
{
buffer_lock = xSemaphoreCreateMutex();
generator_attachment_lock = xSemaphoreCreateMutex();
xSemaphoreGive(buffer_lock);
xSemaphoreGive(generator_attachment_lock);
xTaskCreate(generator_task, ...);
xTaskCreate(magic_printer_task, ..., "Button1");
xTaskCreate(magic_printer_task, ..., "Button2");
}
//MOCK
bool value_is_magic(int32_t value) {return (value % 5 == 0); }
//MOCK
bool button_pressed(char* btnName) { return random() % 50 == 0; }