How can I wake up one process from the wait queue?
Hi, everyoneI am implementing a simple driver to experiment with wait queue.Two
or more read processes block until a write process changes a flag and call
wake_up_interruptible().I expect that a write process will only wake up one
read process.However, once a write process calls wake_up_interruptible() , all
the read processes are awaken. How can I wake up one process from the wait
queue? Here is the snippet of the simple dirver(just for experimenting, kernel
2.6.18):
static ssize_t rlwait_read(struct file *filp, char __user *userp, size_t size,
loff_t *off){struct rlwait_t *rock = (struct rlwait_t *)filp-private_data;
DECLARE_WAITQUEUE(wait, current);add_wait_queue(rock-r_wait_head,
wait);while (rock-r_flag == 0) {
set_current_state(TASK_INTERRUPTIBLE);schedule();}
remove_wait_queue(rock-r_wait_head, wait);
set_current_state(TASK_RUNNING);return 0;}
static ssize_t rlwait_write(struct file *filp, const char __user *userp, size_t
size, loff_t *off){struct rlwait_t *rock = (struct rlwait_t
*)filp-private_data;rock-r_flag = 1;
wake_up_interruptible(rock-r_wait_head);return size; }
Thans in advice.___
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Re: How can I wake up one process from the wait queue?
Hi
You got to use exclusive wait queues here. Needs a bit more lines but
you can specify exactly how many tasks you want woken up.
You should be able to look it up easily on how to use it.
On Thu, Oct 30, 2014 at 2:02 PM, Rock Lee rocklee_...@sina.com wrote:
Hi, everyone
I am implementing a simple driver to experiment with wait queue.Two or more
read processes block until a write process changes a flag and call
wake_up_interruptible().I expect that a write process will only wake up one
read process.However, once a write process calls wake_up_interruptible() ,
all the read processes are awaken. How can I wake up one process from the
wait queue? Here is the snippet of the simple dirver(just for experimenting,
kernel 2.6.18):
static ssize_t rlwait_read(struct file *filp, char __user *userp, size_t
size, loff_t *off)
{
struct rlwait_t *rock = (struct rlwait_t *)filp-private_data;
DECLARE_WAITQUEUE(wait, current);
add_wait_queue(rock-r_wait_head, wait);
while (rock-r_flag == 0) {
set_current_state(TASK_INTERRUPTIBLE);
schedule();
}
remove_wait_queue(rock-r_wait_head, wait);
set_current_state(TASK_RUNNING);
return 0;
}
static ssize_t rlwait_write(struct file *filp, const char __user *userp,
size_t size, loff_t *off)
{
struct rlwait_t *rock = (struct rlwait_t *)filp-private_data;
rock-r_flag = 1;
wake_up_interruptible(rock-r_wait_head);
return size;
}
Thans in advice.
___
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--
---P.K.S
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Re: How can I wake up one process from the wait queue?
On Thursday 30 October 2014 02:02 PM, Rock Lee wrote: Hi, everyone I am implementing a simple driver to experiment with wait queue.Two or more read processes block until a write process changes a flag and call wake_up_interruptible().I expect that a write process will only wake up one read process.However, once a write process calls wake_up_interruptible() , all the read processes are awaken. How can I wake up one process from the wait queue? You can use exclusive wait queues, which wakes up only one process from the queue. Although the general idea that is followed is: all the process are woken up once the resource is made available. And then the access to that resource is guarded by a lock, which in turn allows only one process to access the resource. Rest of the processes are pushed backed to sleep(or busy wait). --- [ C-DAC is on facebook. Kindly follow us on the following url: https://www.facebook.com/CDACINDIA ] This e-mail is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email is strictly prohibited and appropriate legal action will be taken. --- --- [ C-DAC is on Social-Media too. Kindly follow us at: Facebook: https://www.facebook.com/CDACINDIA Twitter: @cdacindia ] This e-mail is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email is strictly prohibited and appropriate legal action will be taken. --- ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
回复：Re: How can I wake up one process from the wait queue?
Hi, Raghavendra, pranjas: Thanks for your reply, add_wait_queue_exclusive() is perfect. - 原始邮件 - 发件人：Raghavendra ar...@cdac.in 收件人：kernelnewbies@kernelnewbies.org 主题：Re: How can I wake up one process from the wait queue? 日期：2014年10月30日 16点52分 On Thursday 30 October 2014 02:02 PM, Rock Lee wrote: Hi, everyone I am implementing a simple driver to experiment with wait queue.Two or more read processes block until a write process changes a flag and call wake_up_interruptible().I expect that a write process will only wake up one read process.However, once a write process calls wake_up_interruptible() , all the read processes are awaken. How can I wake up one process from the wait queue? You can use exclusive wait queues, which wakes up only one process from the queue. Although the general idea that is followed is: all the process are woken up once the resource is made available. And then the access to that resource is guarded by a lock, which in turn allows only one process to access the resource. Rest of the processes are pushed backed to sleep(or busy wait). --- ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
