On Mon, Feb 08, 2016 at 10:51:55AM -0800, Hollis Blanchard wrote: > Previously, trace record files (created by st_set_trace_file_enabled(true)) > were created by the simple backend at initialization time, even if no events > were actually enabled. > > As a consequence, the working directory would become littered with trace-PID > files just by enabling the simple backend at configure time, even when no > -trace options were used. > > --- > I've been using this to avoid creation of empty trace record files. I haven't > done any scientific performance studies, but an extra function > call/conditional/return when recording every trace event doesn't seem to have > any noticeable effect. > > Signed-off-by: Hollis Blanchard <hollis_blanch...@mentor.com> > --- > trace/simple.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/trace/simple.c b/trace/simple.c > index 3fdcc82..67ccc3c 100644 > --- a/trace/simple.c > +++ b/trace/simple.c > @@ -209,6 +209,8 @@ int trace_record_start(TraceBufferRecord *rec, > TraceEventID event, size_t datasi > uint64_t event_u64 = event; > uint64_t timestamp_ns = get_clock(); > > + st_set_trace_file_enabled(true);
trace_record_start() can be called from multiple threads. st_set_trace_file_enabled() is not thread-safe. One way to solve this is to use a read memory barrier to fetch trace_fp. If it's NULL then acquire trace_lock and recheck (in case another thread has modified it since). Now continue with the rest of st_set_trace_file_enabled() to open the file. If multiple threads pile up they will just wait for trace_lock until the first thread has completed opening the file. Or you could use try_lock instead and return -EBUSY to drop those events similar to the -ENOSPC error case in trace_record_start(). Stefan
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