Multithreading

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Build Configuration

When building newlib, the configuration --enable-newlib-multithread needs to be added to enable multithreading support. It is enabled by default.

The header file reent.h in Newlib defines the structure struct _reent to support multithreading:

By default, Newlib defines a global structure variable impure_data, defined in newlib/libc/reent/impure.c, and represented by the macro _REENT;
struct _reent defines some C standard variables, such as errno, stdin, stdout, stderr, etc.;
To support multiple threads accessing their own errno, stdin, stdout, stderr, etc., a member of type struct _reent needs to be added to the thread object structure;
Due to the large size of struct _reent, XWOS implements struct _reent itself;
In addition to providing functions from the C standard, Newlib also defines versions of functions with the _r suffix, such as _read_r(), which have an additional struct _reent * parameter to distinguish between different threads.