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test/log: fix for crash with libc++ #20233

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Feb 6, 2018
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test/log: fix for crash with libc++ #20233

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2 changes: 1 addition & 1 deletion src/log/test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ TEST(Log, ReuseBad)
{
auto e = log.create_entry(l, 1);
auto& out = e->get_ostream();
out << (const char*)nullptr;
out << (std::streambuf*)nullptr;
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@tchaikov tchaikov Feb 1, 2018 •
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@cbodley after a second thought, i feel that we are covering potential bugs. if we fail to print a logging message because of the badbit set by previous logging message printed using this TLS stream instance, it is a sign that we have a programming error when printing logging messages. because we should not print a (std::streambuf*)nullptr, should we?

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As the person who noticed this bug, and having thought about this line of reasoning, I'd prefer that we reset the stream. The fact that in libstdc++ environments "nothing happens" other than recoverable stream failure after sending the nullptr, means that attention may not be drawn to a future case where we send bad data. If a case does slip in, the stream reset makes it easier to find, as well as remediating the damage.

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Performance cost of the reset would be a strong reason not to do it, though. I suspect that's not an issue though?

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@mattbenjamin badbit denotes irrecoverable error. so all following logging messages won't be printed. so i guess it'd be relatively easy to track back to the offending log line which was not printed?

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@mattbenjamin @tchaikov
Without clear() on stream:
[ RUN ] Log.Speed_gather
[ OK ] Log.Speed_gather (1222 ms)
[ RUN ] Log.Speed_nogather
[ OK ] Log.Speed_nogather (46 ms)

With clear() on stream:
[ RUN ] Log.Speed_gather
[ OK ] Log.Speed_gather (1247 ms)
[ RUN ] Log.Speed_nogather
[ OK ] Log.Speed_nogather (45 ms)

Before TLS optimizations:
[ RUN ] Log.Speed_gather
[ OK ] Log.Speed_gather (1636 ms)
[ RUN ] Log.Speed_nogather
[ OK ] Log.Speed_nogather (49 ms)

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@aclamk thank you for profiling this change. i don't feel strong either way then.

EXPECT_TRUE(out.bad()); // writing nullptr to a stream sets its badbit
log.submit_entry(e);
}
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