Threads #

Introduction #

Threads allow a robot to run multiple tasks simultaneously within the same program. They enable multitasking, letting the robot perform independent actions at the same time.

Class Constructors #

1 — Creates and starts a new thread with a function.
thread( void (* callback)(void) );

2 — Creates and starts a new thread with a function that accepts an argument.
thread( int (* callback)(void *), void *arg );

Class Destructor #

Destroys the thread object and releases associated resources.

~thread();

Parameters #

Parameter	Type	Description
`callback`	`void (*)(void)`	A previously defined function that will run in the new thread.
`callback`	`int ()(void )`	A previously defined function that accepts a void pointer argument and will run in the new thread.
`arg`	`void *`	A void pointer that is passed to the callback function.

Notes #

A function must always be defined before it is called.
When you create a thread, you can name it to manage it individually in your project.
Once a thread is stopped using interrupt(), it cannot be restarted. To run it again, you must create a new thread.

Example #

Define the function (outside of int main())

// Drive forward while blinking screen
void blinkScreen() {
  while (true) {
    Brain.Screen.clearScreen(red);
    wait(0.5, seconds);
    Brain.Screen.clearScreen();
    wait(0.5, seconds);
  }
}

int main() {
  /* vexcodeInit() is only required when using VEXcode.
  Remove vexcodeInit() if compiling in VS Code. */
  vexcodeInit();

  // Begin project code
  thread blinkScreenThread = thread(blinkScreen);
  Drivetrain.drive(forward);
}

Define the function (outside of int main())

// Run multiple threads simultaneously
// Turn right, blink screen at once
void blinkScreen() {
  while (true) {
    Brain.Screen.clearScreen(red);
    wait(0.5, seconds);
    Brain.Screen.clearScreen();
    wait(0.5, seconds);
  }
}

void turning() {
  Drivetrain.turn(right);
}

int main() {
  /* vexcodeInit() is only required when using VEXcode.
  Remove vexcodeInit() if compiling in VS Code. */
  vexcodeInit();

  // Begin project code
  thread blinkScreenThread = thread(blinkScreen);
  thread turningThread = thread(turning);
}

Member Functions #

The thread class includes the following member functions:

interrupt – Stops a thread manually, useful for halting background behavior.

interrupt #

Stops a thread manually, which is useful when a task is no longer needed or when a program needs to reset or reassign threads.

Available Functions

void interrupt();

Parameters

This function does not have parameters.

Return Values

This function does not return a value.

Notes

Once a thread is stopped, it cannot be restarted. To run it again, you must create a new thread using thread.
This is useful when a task is no longer needed or when a program needs to reset or reassign threads.

Examples

Define the function (outside of int main())

// Loop through red and green
void colorLoop() {
  while (true) {
    Brain.Screen.drawRectangle(0, 120, 480, 120, red);
    wait(0.5, seconds);
    Brain.Screen.drawRectangle(0, 120, 480, 120, green);
    wait(0.5, seconds);
  }
}

// Display the current heading
void displayHeading() {
  Brain.Screen.setFont(prop60);
  while (true) {
    Brain.Screen.clearLine(1);
    Brain.Screen.setCursor(1, 1);
    Brain.Screen.print(
      "Heading: %.1f",
      DrivetrainInertial.heading(degrees)
    );
    wait(50, msec);
  }
}

int main() {
  /* vexcodeInit() is only required when using VEXcode.
  Remove vexcodeInit() if compiling in VS Code. */
  vexcodeInit();

  // Turn right, change screen color, and display heading at once
  thread colorThread = thread(colorLoop);
  thread displayHeadingThread = thread(displayHeading);

  Drivetrain.turn(right);
  wait(2, seconds);

  // Stop the flashing colors
  colorThread.interrupt();
}