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NAME

init_sleepqueues

 
sleepq_abort

 
sleepq_add

 
sleepq_alloc

 
sleepq_broadcast

 
sleepq_calc_signal_retval

 
sleepq_catch_signals

 
sleepq_free

 
sleepq_lock

 
sleepq_lookup

 
sleepq_release

 
sleepq_remove

 
sleepq_signal

 
sleepq_set_timeout

 
sleepq_timedwait

 
sleepq_timedwait_sig

 
sleepq_wait

 
sleepq_wait_sig

 - manage the queues of sleeping threads

 

SYNOPSIS

DESCRIPTION

The sleepq_alloc ();
function allocates an inactive sleep queue and is used to assign a sleep queue to a thread during thread creation. The sleepq_free ();
function frees the resources associated with an inactive sleep queue and is used to free a queue during thread destruction.

Active sleep queues are stored in a hash table hashed on the addresses pointed to by wait channels. Each bucket in the hash table contains a sleep queue chain. A sleep queue chain contains a spin mutex and a list of sleep queues that hash to that specific chain. Active sleep queues are protected by their chain's spin mutex. The init_sleepqueues ();
function initializes the hash table of sleep queue chains.

The sleepq_lock ();
function locks the sleep queue chain associated with wait channel Fa wchan .

The sleepq_lookup ();
returns a pointer to the currently active sleep queue for that wait channel associated with Fa wchan or NULL if there is no active sleep queue associated with argument Fa wchan . It requires the sleep queue chain associated with Fa wchan to have been locked by a prior call to sleepq_lock (.);

The sleepq_release ();
function unlocks the sleep queue chain associated with wchan ();
and is primarily useful when aborting a pending sleep request before one of the wait functions is called.

The sleepq_add ();
function places the current thread on the sleep queue associated with the wait channel Fa wchan . The sleep queue chain associated with argument Fa wchan must be locked by a prior call to sleepq_lock ();
when this function is called. If a lock is specified via the Fa lock argument, and if the kernel was compiled with options INVARIANTS then the sleep queue code will perform extra checks to ensure that the lock is used by all threads sleeping on Fa wchan . The Fa wmesg parameter should be a short description of Fa wchan . The Fa flags parameter is a bitmask consisting of the type of sleep queue being slept on and zero or more optional flags. The Fa queue parameter specifies the sub-queue, in which the contending thread will be inserted.

There are currently three types of sleep queues:

SLEEPQ_CONDVAR

A sleep queue used to implement condition variables.

SLEEPQ_SLEEP

A sleep queue used to implement sleep(9), wakeup(9) and wakeup_one9.

SLEEPQ_PAUSE

A sleep queue used to implement pause(9).

There is currently only one optional flag:

SLEEPQ_INTERRUPTIBLE

The current thread is entering an interruptible sleep.

A timeout on the sleep may be specified by calling sleepq_set_timeout ();
after sleepq_add (.);
The Fa wchan parameter should be the same value from the preceding call to sleepq_add (,);
and the sleep queue chain associated with Fa wchan must have been locked by a prior call to sleepq_lock (.);
The Fa timo parameter should specify the timeout value in ticks.

The current thread may be marked interruptible by calling sleepq_catch_signals ();
with Fa wchan set to the wait channel. This function returns a signal number if there are any pending signals for the current thread and 0 if there is not a pending signal. The sleep queue chain associated with argument Fa wchan should have been locked by a prior call to sleepq_lock (.);

Once the thread is ready to suspend, one of the wait functions is called to put the current thread to sleep until it is awakened and to context switch to another thread. The sleepq_wait ();
function is used for non-interruptible sleeps that do not have a timeout. The sleepq_timedwait ();
function is used for non-interruptible sleeps that have had a timeout set via sleepq_set_timeout (.);
The sleepq_wait_sig ();
function is used for interruptible sleeps that do not have a timeout. The sleepq_timedwait_sig ();
function is used for interruptible sleeps that do have a timeout set. The Fa wchan argument to all of the wait functions is the wait channel being slept on. The sleep queue chain associated with argument Fa wchan needs to have been locked with a prior call to sleepq_lock (.);
The Fa signal_caught parameter to sleepq_timedwait_sig ();
specifies if a previous call to sleepq_catch_signals ();
found a pending signal.

When the thread is resumed, the wait functions return a non-zero value if the thread was awakened due to an interrupt other than a signal or a timeout. If the sleep timed out, then Er EWOULDBLOCK is returned. If the sleep was interrupted by something other than a signal, then some other return value will be returned. If zero is returned after resuming from an interruptible sleep, then sleepq_calc_signal_retval ();
should be called to determine if the sleep was interrupted by a signal. If so, sleepq_calc_signal_retval ();
returns Er ERESTART if the interrupting signal is restartable and Er EINTR otherwise. If the sleep was not interrupted by a signal, sleepq_calc_signal_retval ();
will return 0.

A sleeping thread is normally resumed by the sleepq_broadcast ();
and sleepq_signal ();
functions. The sleepq_signal ();
function awakens the highest priority thread sleeping on a wait channel while sleepq_broadcast ();
awakens all of the threads sleeping on a wait channel. The Fa wchan argument specifics which wait channel to awaken. The Fa flags argument must match the sleep queue type contained in the Fa flags argument passed to sleepq_add ();
by the threads sleeping on the wait channel. If the Fa pri argument does not equal -1, then each thread that is awakened will have its priority raised to Fa pri if it has a lower priority. The sleep queue chain associated with argument Fa wchan must be locked by a prior call to sleepq_lock ();
before calling any of these functions. The Fa queue argument specifies the sub-queue, from which threads need to be woken up.

A thread in an interruptible sleep can be interrupted by another thread via the sleepq_abort ();
function. The Fa td argument specifies the thread to interrupt. An individual thread can also be awakened from sleeping on a specific wait channel via the sleepq_remove ();
function. The Fa td argument specifies the thread to awaken and the Fa wchan argument specifies the wait channel to awaken it from. If the thread Fa td is not blocked on the the wait channel Fa wchan then this function will not do anything, even if the thread is asleep on a different wait channel. This function should only be used if one of the other functions above is not sufficient. One possible use is waking up a specific thread from a widely shared sleep channel.

The sleep queue interface is currently used to implement the sleep(9) and condvar(9) interfaces. Almost all other code in the kernel should use one of those interfaces rather than manipulating sleep queues directly.  

SEE ALSO

Index

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO

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