Re: Problem of newlib running on the SMP platform.

[Jeff Johnston <jjohnstn at redhat dot com>]

Hao Shen wrote:
> Hi, everybody,
>
> I have found a problem about newlib running on the SMP platform.
> First I describe my design environment here.
> 1. SMP platform shares the same memory and used the same memory address.
> 2. We have our SMP operating system which provide multi-thread and locks.
> 3. In the simulation, I found that the two threads in two different
> CPUs enter the same system call at the same time. For example, both
> threads call the "printf" and the output is terrible.
>
> I have read some mails of newlib before. People suggest use
> _impure_ptr and _reent. For my situation should I
> 1. Use two different _reent for two CPUs?
> 2. Use a different _reent for each thread?
> 3. Use only one _reent in whole system and lock it to guarantee only
> one thread is using system call at the same time.
>
> I am waiting for the answers.

Number 2.  Each thread should have its own __reent struct.  If you set 
the magic flag: __DYNAMIC_REENT__ in libc/include/sys/config.h for your 
platform/OS, then the default _REENT macro gets mapped to be a function 
call to __get_reent() (e.g. i386 linux sets this flag on).  You need to 
provide the __getreent() function which returns a _reent struct for the 
current thread.  How you do the mapping is up to you (e.g. you could use 
a thread local storage area).

-- Jeff J.