[GitHub] [incubator-nuttx] xiaoxiang781216 commented on issue #3599: Syslog thread-safety

[GitBox <gi...@apache.org>]

xiaoxiang781216 commented on issue #3599:
URL: https://github.com/apache/incubator-nuttx/issues/3599#issuecomment-825555585


   > Its root cause is that `nx_vsyslog()` does not execute atomically. It makes multiple unprotected calls to `lib_sprintf()`.
   > So, if two threads are logging simultaneously, their respective calls to `lib_sprintf()` will interfere with each other.
   > 
   
   This can be fixed by va_format extension from linux kernel:
   ```
   struct va_format
   
   	%pV
   
   For printing struct va_format structures. These contain a format string
   and va_list as follows:
   	struct va_format {
   		const char *fmt;
   		va_list *va;
   	};
   
   Implements a "recursive vsnprintf". And here is an implementation I made recently:
   https://github.com/j256/dmalloc/pull/89/commits/6f4d29da098e985ab284b837eb5e45009f1b45e8#diff-e7a46ef823b649b77cffce4a4a8d4cbe508b35c6ce4fc54ebc39a1d1895ad85cR378-R384
   https://github.com/j256/dmalloc/pull/89/commits/6f4d29da098e985ab284b837eb5e45009f1b45e8#diff-f2e6c18de8171e389aeff0b8d25b2755253108a59a13baf7167c2ffa0af36a58R529-R537
   
   > 
   > **Semaphore**
   
   semaphore isn't enough here, we need the critical section to sync with the interrupt handle. Since the critical section will block all hardware interrupt process, and the serial is very slow, the lock will make a significant impact on the runtime behaviour.


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