From: ÀîºêÁÁ (lihongliang070_at_tom.com)
Date: Fri Jun 05 2009 - 22:33:39 PDT
Hello professor:
There is a problem which has been puzzling me all the time when I read the code of BLCR, Everytime I met with those part of the code I just try to understand it , but still can not understand it very well. Now I think it¡¯s time to consult you about the ¡°Cr_barrier¡±.
For example: code section in cr_dump_self:
/* Now use vmadump to write out the state for the thread.
ALL threads call this and serialization is done within */
...
bytes = cr_freeze_threads(proc_req, 0, i_am_leader);
if (bytes < 0) {
result = (int)bytes;
...
cr_barrier_notify(&proc_req->vmadump_barrier);
goto out;
}
CR_KTRACE_LOW_LVL("thread finished vmadump");
/* Need a barrier here to ensure all threads write their regs before the next
* write to the file.
*/
if (cr_barrier_enter(&proc_req->vmadump_barrier)) {
CR_KTRACE_LOW_LVL("process finished vmadump");
}
It seemed to use cr_barrier_enter to ensure all threads write their regs before the next write to the file. Why can not a thread continue to write before all threads write their regs just through invoking this function? I know it use semaphore & condition Variables ? Can you help me to understand how it works?
I will be very greateful if you can introduce more about ¡°barrier¡± to me systematially . Please forgive me if you think it as an excessive demand. Thank you.