Index

Cooperating Sequential Tasks

  1. Introduction
    1. Arduino
    2. Interrupts
  2. Simple Tasks
  3. Multiple Tasks
  4. Communicating Tasks
  5. Communicating Values
  6. Synchronising Tasks
  7. Buffered Communication
  8. Multiple Senders
  9. Conditional Tasks
  10. Transput
  11. Implementation
    1. Common Data
    2. Tasks
    3. task_builder
    4. task
    5. channel
    6. virtual_machine
    7. set
    8. queue
    9. clock
    10. standard
    11. Adjusting Limits
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set



Sets of task identifiers are used by a number of components of the multitasking library, e.g. the set of waiting tasks and the set of active receivers associated with a channel.

Data Structure

Sets are stored in a structure with only one field of type unsigned integer used to represent the members of the set. Each bit in the members field represents the presence or absence of a task in the set, e,g, if bit 3 is set, the task with identifier 3 is a member of the set, and if bit 3 is cleared then the task with identifier 3 is not a member of the set.

Arduino variables of type integer contain 16 bits. This limits the number of tasks that can be stored in a set to 16 with identifiers to from 0 to 15.

struct set
{
  unsigned int members;
};


Functions

Sets support the following functions. For consistency, all of the set functions take pointers to structures of type set so that the members field can be updated when required.

init_set

void init_set(set* s);


This function makes a set empty by removing all task identifiers from it.

insert

void insert(set* s, byte id);


remove

This function inserts the identifier of a task into the set. If the task is already a member the set, this causes no change.

byte remove(set* s, byte id);


This function removes the identifier of a task from the set. If the task is not a member of the set, this causes no change.

in_set

bool in_set(set* s, byte id);


This function returns true if the supplied identifier is a member of the set. Otherwise it returns false.

in_set

bool in_set(set* s1, set* s2);


This function returns true if all the members of the set s2 are also members of the set s1, i.e. s2 is a proper subset of s1. It returns false otherwise.

empty_set

bool empty_set(set* s);


This function returns true if the set has no members, and false otherwise.