21 Feb

Thread Dump Format

The print_thread_state() function in the avr_oxide::util::debug module can be used to print a dump of all currently running threads to the panicout serial port.

A typical thread dump looks something like this:

T0:
  bgd
  RC: 0
  Wt:
  ST:
    OK
    S: 64
    T: 12033
    F: 44

T1:
  RDY
  RC: 0
  Wt:
  ST:
    OK
    S: 512
    T: 12555
    F: 204

T2:
  Zby
  RC: 123
  Wt:
  ST:
    OK
    S: 1024
    T: 13609
    F: 884

T3:
  RDY
  RC: 0
  Wt:
  ST:
    OK
    S: 256
    T: 14181
    F: 207

This shows a total of four threads - two are ready (will be scheduled for execution,) one is a zombie, and finally the background Idle thread (which must always be present). For each thread we can see the state, and also the current status of the stack allocated to that thread.

Anatomy of an individual thread

The meaning of each line explained:

Data	Meaning
`T2:`	Thread ID
`Zby`	Thread status, in this case Zombie
`RC:123`	Thread return code, if the thread is completed (otherwise 0)
`Wt:`	List of thread IDs waiting to join this thread, if any
`ST:`	Stack status follows
`OK`	Status of the stack: `OK`, or `BAD` if the stack has overflowed
`S:1024`	Stack size, in bytes
`T:13609`	Address of the top of the stack in memory
`F:884`	Number of bytes free/unused in this stack

Thread Status

The following mnemonics are used to represent possible thread status:

Code	Meaning
`RDY`	Ready to execute
`bgd`	Ready to execute at background priority (only scheduled if no threads are `RDY`)
`Sus`	Suspended/cannot be scheduled
`Zby`	Zombie; thread has exited, but before it can be freed another thread must `join()` it
`XXX`	Thread is dead. It consumes no resources, and may be replaced by a subsequent `spawn()`
`B:M`	Blocked on a Mutex
`B:T`	Blocked waiting to `join()` another thread
`B:Q`	Blocked on a Queue (waiting for an event or I/O)
`B:E`	Blocked on an EventWait object

Tim Walls