• Karsten Blees's avatar
    trace: add infrastructure to augment trace output with additional info · c69dfd24
    Karsten Blees authored
    To be able to add a common prefix or suffix to all trace output (e.g.
    a timestamp or file:line of the caller), factor out common setup and
    cleanup tasks of the trace* functions.
    
    When adding a common prefix, it makes sense that the output of each trace
    call starts on a new line. Add '\n' in case the caller forgot.
    
    Note that this explicitly limits trace output to line-by-line, it is no
    longer possible to trace-print just part of a line. Until now, this was
    just an implicit assumption (trace-printing part of a line worked, but
    messed up the trace file if multiple threads or processes were involved).
    
    Thread-safety / inter-process-safety is also the reason why we need to do
    the prefixing and suffixing in memory rather than issuing multiple write()
    calls. Write_or_whine_pipe() / xwrite() is atomic unless the size exceeds
    MAX_IO_SIZE (8MB, see wrapper.c). In case of trace_strbuf, this costs an
    additional string copy (which should be irrelevant for performance in light
    of actual file IO).
    
    While we're at it, rename trace_strbuf's 'buf' argument, which suggests
    that the function is modifying the buffer. Trace_strbuf() currently is the
    only trace API that can print arbitrary binary data (without barfing on
    '%' or stopping at '\0'), so 'data' seems more appropriate.
    Signed-off-by: default avatarKarsten Blees <[email protected]>
    Signed-off-by: default avatarJunio C Hamano <[email protected]>
    c69dfd24
trace.c 5.21 KB