Mailbox

Mailbox
A message or message pointer from a task that is addressed to another task .

Message Queue

Message Queue
A task sending the multiple FIFO or priority messages into a queue for use by another task using queue messages as an input.

Deadlock Situation

Deadlock Situation

A task waiting for some semaphore the release of a semaphore from a task and another different task waiting for another semaphore release to run. None of these is able to proceed further . An operating system can take care of this is by appropriate provisions. 

Priority Inversion

Priority Inversion 
A problem in which a low priority task inadvertently does not release the process for higher priority task. An operation system can take care of this it by appropriate provisions. 

P and V semaphore

P and V semaphore 
The semaphore functions defined as mutex or counting semaphore , or to solve the classical producer- consumer problem when using a bounded buffer. 

Buffer

Buffer
A memory block for a queue or list of messages or stream of bytes between and output source and input sink, for examples, between the tasks, files, computer and printer, physical devices and network.

Counting Semaphore

Counting Semaphore
A semaphore in which the value of which can be incremented and decremented and which is not a Boolean variable.