Detailed description of wait_event () function set

The wait_event () function is often used to block the current running process to see how to implement the wait_event () function in the Linux kernel.

First, we will introduce several macro-defined functions:

1. # define define_wait_func (name, function )\

Wait_queue_t name = {\

. Private = Current ,\

. Func = function ,\

. Task_list = list_head_init (name). task_list ),\

}

2. # define define_wait (name )\

Define_wait_func (name, autoremove_wake_function)

3. # define init_wait (name )\

Do {\

(Name)-> private = current ;\

(Name)-> func = autoremove_wake_function ;\

Init_list_head (& name-> task_list );

} While (0)

Therefore, define_wait (name) defines a wait_queue_t struct and hooks it with the currently running process, at the same time, it defines the processing function autoremove_wake_function () after the current process is awakened ().

Wait_event () function implementation:

# DEFINE _ wait_event (WQ, condition )\

Do {\

Define_wait (_ Wait); \ defines and initializes a wait_queue_t

For (;;)\

{\

Prepare_to_wait (& WQ, & __ wait, task_uninterruptible );\

If (condition )\

Break ;\

Schedule ();\

}

Finish_wait (& WQ, & __ wait );\

}While (0)

# Define wait_event (WQ, condition )\

Do {\

If (condition )\

Break ;\

_ Wait_event (WQ, condition );\

}While (0)

Wait_event_timeout () function implementation:

# DEFINE _ wait_event_timeout (WQ, condition, RET )\

Do {\

Define_wait (_ Wait );\

For (;;)\

{\

Prepare_to_wait (& WQ, & __ wait, task_uninterruptible );\

If (conditon )\

Break ;\

Ret = schedule_timeout (RET );\

If (! RET )\

Break ;\

}

Finish_wait (& WQ, & __ wait );\

} While (0)

# Define wait_event_timeout (WQ, conditon, timeout )\

(Long _ ret = timeout ;\

If (! Condition )\

_ Wait_event_timeout (WQ, conditon, _ RET );\

_ Ret ;)

Detailed description of wait_event () function set