Here's the complete list of kernel blocking states, with brief explanations of each state.
By the way, this list is available in <sys/states.h>—you'll notice that the states are all prefixed with STATE_ , but the prefix tends to be omitted in conversation and the documentation (for example, “READY” is really STATE_READY):
| If the state is: | The thread is: |
|---|---|
| STATE_CONDVAR | Waiting for a condition variable to be signaled |
| STATE_DEAD | Dead. Kernel is waiting to release the thread's resources |
| STATE_INTR | Waiting for an interrupt |
| STATE_JOIN | Waiting for the completion of another thread |
| STATE_MUTEX | Waiting to acquire a mutex |
| STATE_NANOSLEEP | Sleeping for a period of time |
| STATE_NET_REPLY | Waiting for a reply to be delivered across the network |
| STATE_NET_SEND | Waiting for a pulse or message to be delivered across the network |
| STATE_READY | Not running on a CPU, but is ready to run (one or more higher or equal priority threads are running) |
| STATE_RECEIVE | Waiting for a client to send a message |
| STATE_REPLY | Waiting for a server to reply to a message |
| STATE_RUNNING | Actively running on a CPU |
| STATE_SEM | Waiting to acquire a semaphore |
| STATE_SEND | Waiting for a server to receive a message |
| STATE_SIGSUSPEND | Waiting for a signal |
| STATE_SIGWAITINFO | Waiting for a signal |
| STATE_STACK | Waiting for more stack to be allocated |
| STATE_STOPPED | Suspended (SIGSTOP signal) |
| STATE_WAITCTX | Waiting for a register context (usually floating point) to become available (only on SMP systems) |
| STATE_WAITPAGE | Waiting for process manager to resolve a fault on a page |
| STATE_WAITTHREAD | Waiting for a thread to be created |
The important thing to keep in mind is that when a thread is blocked, regardless of which state it's blocked in, it consumes no CPU. Conversely, the only state in which a thread consumes CPU is in the RUNNING state.
We'll see the SEND, RECEIVE, and REPLY blocked states in the Message Passing chapter. The NANOSLEEP state is used with functions like sleep(), which we'll look at in the chapter on Clocks, Timers, and Getting a Kick Every So Often. The INTR state is used with InterruptWait(), which we'll take a look at in the Interrupts chapter. Most of the other states are discussed in this chapter.