Blocked thread information

When a thread is blocked, there's an additional set of fields that are important (they are within the debug_thread_t, above, where the comment says "blocking information deleted"). The deleted content is:

  union {

    struct {
      pthread_t   tid;
    } join;

    struct {
      _Int32t     id;
      _Uintptrt   sync;
    } sync;

    struct {
      _Uint32t    nd;
      pid_t       pid;
      _Int32t     coid;
      _Int32t     chid;
      _Int32t     scoid;
    } connect;

    struct {
      _Int32t     chid;
    } channel;

    struct {
      pid_t       pid;
      _Uintptrt   vaddr;
      _Uint32t    flags;
    } waitpage;

    struct {
      _Uint32t    size;
    } stack;

  } blocked;

As you can see, there are six major structures (join, sync, connect, channel, waitpage, and stack) that are unioned together (because a thread can be in only one given blocking state at a time):

join

When a thread is in STATE_JOIN, it's waiting to synchronize to the termination of another thread (in the same process). This thread is waiting for the termination of the thread identified by the tid member.

sync

When a thread is blocked on a synchronization object (such as a mutex, condition variable, or semaphore), the id member indicates the virtual address of the object, and the sync member indicates the type of object.

connect

Indicates who the thread is blocked on (used with STATE_SEND and STATE_REPLY).

channel

Indicates the channel ID the thread is blocked in (used with STATE_RECEIVE).

waitpage

Indicates the virtual address that the thread is waiting for to be lazy-mapped in (used with STATE_WAITPAGE).

stack

Used with STATE_STACK, indicates the thread is waiting for size bytes of virtual address space to be made available for the stack.