[GitHub] [incubator-nuttx] xiaoxiang781216 edited a comment on pull request #4028: syslog: fix log confusion when multi task writing together

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xiaoxiang781216 edited a comment on pull request #4028:
URL: https://github.com/apache/incubator-nuttx/pull/4028#issuecomment-872989530


   > Hi @Donny9
   > 
   > I had a look at the changes, but I don't think that this will fix the issue.
   > The problem is not the thread safety of the drivers, rather the multiple calls to `lib_sprintf()`.
   > See #3599.
   
   lib_sprintf format result to lib_syslogstream_s, two cases here:
   
   1. CONFIG_SYSLOG_BUFFER equals y, syslogstream_flush output the log through syslog_write
   2. CONFIG_SYSLOG_BUFFER equals n, syslogstream_addchar output the log through syslog_putc
   
   This patch only address the mess issue in case 1. The lock ensure that the caller of syslog_write don't interlace with each other.
   
   > 
   > Adding a `sc_write()` to all channels seems a good way forward.
   > If `syslog_write_t` is modified to also accept a `force` flag, we can eliminate the `syslog_putc_t` too.
   >
   
   Yes, but sc_putc/sc_force_putc is more simpler to implement than sc_write.
    
   > But I think a semaphore at this place will not solve the actual issue. Depending on the solution to the initial problem, it may not be needed at all.
   > 
   > Do you have any plans for further development on this?
   > (I have also spent quite some time thinking about this and experimenting, but I haven't reached a "good" final implementation...)
   
   Case 1 should be addressed by:
   
   1. syslog driver self(e.g. ramlog, devlog), if it provide the multithread safe sc_write
   2. syslog_default_write with this patch
   
   But, it's impossible to fix case 2.
   
   


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