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[SDK] Fix core dump issue in OTEL_INTERNAL_LOG_DISPATCH macro #2394

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[SDK] Fix core dump issue in OTEL_INTERNAL_LOG_DISPATCH macro #2394

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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,8 @@ Increment the:
[#2385](https://github.com/open-telemetry/opentelemetry-cpp/pull/2385)
* [API] Add a new AddLink() operation to Span
[#2380](https://github.com/open-telemetry/opentelemetry-cpp/pull/2380)
* [SDK] Fix core dump issue in OTEL_INTERNAL_LOG_DISPATCH macro
[#2394](https://github.com/open-telemetry/opentelemetry-cpp/pull/2394)

Important changes:

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37 changes: 19 additions & 18 deletions sdk/include/opentelemetry/sdk/common/global_log_handler.h
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Expand Up @@ -137,24 +137,25 @@ OPENTELEMETRY_END_NAMESPACE
* To ensure that GlobalLogHandler is the first one to be initialized (and so last to be
* destroyed), it is first used inside the constructors of TraceProvider, MeterProvider
* and LoggerProvider for debug logging. */
#define OTEL_INTERNAL_LOG_DISPATCH(level, message, attributes) \
do \
{ \
using opentelemetry::sdk::common::internal_log::GlobalLogHandler; \
using opentelemetry::sdk::common::internal_log::LogHandler; \
if (level > GlobalLogHandler::GetLogLevel()) \
{ \
break; \
} \
const opentelemetry::nostd::shared_ptr<LogHandler> &log_handler = \
GlobalLogHandler::GetLogHandler(); \
if (!log_handler) \
{ \
break; \
} \
std::stringstream tmp_stream; \
tmp_stream << message; \
log_handler->Handle(level, __FILE__, __LINE__, tmp_stream.str().c_str(), attributes); \
#define OTEL_INTERNAL_LOG_DISPATCH(level, message, attributes) \
do \
{ \
using opentelemetry::sdk::common::internal_log::GlobalLogHandler; \
using opentelemetry::sdk::common::internal_log::LogHandler; \
if (level > GlobalLogHandler::GetLogLevel()) \
{ \
break; \
} \
const opentelemetry::nostd::shared_ptr<LogHandler> &log_handler = \
GlobalLogHandler::GetLogHandler(); \
if (!log_handler) \
{ \
break; \
} \
std::stringstream tmp_stream; \
tmp_stream << message; \
std::string tmp_string = tmp_stream.str(); \
log_handler->Handle(level, __FILE__, __LINE__, tmp_string.c_str(), attributes); \
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Probably there is something I missed. What's is different behavior with this change?

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I also didn't get the point, could you please explain this change?
To my understanding, C++ specifications will ensure the temporary object should be freed only after this code block(Handle(...)).

https://en.cppreference.com/w/cpp/language/lifetime#Temporary_object_lifetime

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You're correct.

We've previously encountered a core dump caused by c_str(), similar to the situation described in https://stackoverflow.com/questions/27627413/why-does-calling-c-str-on-a-function-that-returns-a-string-not-work.
The code was as follows:

    auto cstr = tmp_stream.str().c_str();
    f(cstr);

This caused cstr to become an invalid pointer passed into function f.

However, in this case, Handle(level, FILE, LINE, tmp_stream.str().c_str(), attributes) is within a single expression, so this issue doesn't exist.

When I saw this core dump, my habitual aversion to the c_str() function led to a misjudgment.

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Yes, in the example you shared and aslo the stackoverflow link, the temporary object returned from function reaches the end of its lifetime at the end of the including its expression, which means the temporary object is no longer valid after the ";", but the lifetime of local variable is different and will reach the end of current block, like @owent mentioend.

} while (false);

#define OTEL_INTERNAL_LOG_GET_3RD_ARG(arg1, arg2, arg3, ...) arg3
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