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CHAPTER 3 μT-REALOS FUNCTIONS
3.3
Task Synchronization Functions
This section explains the task synchronization functions.
■ Task Synchronization Functions
The task synchronization functions are functions for performing synchronization by directly
operating task portions. Table 3.3-1 shows task synchronization functions and their
corresponding systems calls.
Table 3.3-1 Task Synchronization Functions and Corresponding System Calls
Function
System Call Name
Sleep task
tk_slp_tsk
Wakeup task
tk_wup_tsk
Cancel Wakeup Task
tk_can_wup
Release Wait
tk_rel_wai
Suspend Task
tk_sus_tsk
tk_rsm_tsk
Resume wait task
tk_frsm_tsk (Force Resume Task)
Delay task
tk_dly_tsk
Wakeup requests for a task are queued. That is, when an attempt is made to wake up a task that
is not in the sleep state, the attempt is remembered. After that, when the task is to go to a sleep
state, it does not enter that state. To realize this, the kernel maintains the number of wakeup
requests that have been queued for each task. This is called the "wakeup request queuing
count". When the task is started, this count is cleared to 0.
Futhermore, suspend requests for a task are nested. That is, if a task that is already in the
SUSPENDED state (including WAITING-SUSPENDED state) is placed again in the
SUSPENDED state, the attempt hereof is remembered. After that, when an attempt is made to
resume the task in SUSPENDED state (including WAITING-SUSPENDED state), it is not
resumed. To realize this, the kernel maintains the number of requests of SUSPENDED state
nested for each task. This is called the "suspend request nesting count". When the task is
started, this count is cleared to 0.
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