roq-logging

Output

Always using stdout and stderr.

Synchronicity

Logging is synchronous if the process has an attached terminal. This is normally what you want if you’re launching the program from the command-line.

Loggig is asynchronous if the process has no attached terminal. This benefits the predictability of latency of the running process because it can offload the writing of the message to a secondary thread.

Templates

Logging capabilities are accessed through templates. This is done to capture filename and line number at the point where the log message is being generated.

The template identifies the severity

• log::info(...)

• log::warn(...)

• log::error(...)

• log::critical(...)

In particular, a critical log message will

• try to flush log buffers,

• write a backtrace to stderr,

• abort the running process and

• maybe create a core dump.

There is one more facility

• log::debug(...)

which will only be included when NDEBUG has not been defined.

Formatting

The log message itself is being generated by fmt.

Note

We only support std::string_view for the format string. The reason is that generic strings, and char const * in particular, may imply run-time checking of string length.

Some examples

log::info("Trivial"sv);
log::warn("Latency {} exceeds the threshold of {}"sv, latency, threshold);
log::error(R"(Invalid key="{}")"sv, key);
log::critical("Unexpected"sv);

Verbosity

Verbosity can be controlled by setting the ROQ_v environment variable

Note

Default verbosity level is 0 (zero).

Some examples

log::info<0>("Same as log::info"sv);
log::info<1>("Will only log when ROQ_v >= 1"sv);
log::info<2>("Will only log when ROQ_v >= 2"sv);

Service

struct Service

Convenience class to wrap roq::Logger, absl::flags, etc.

Public Functions

int run()

The main function.

struct Info

Tool

struct Tool

Convenience class to wrap roq::Logger, absl::flags, etc.

Public Functions

int run()

The main function.

struct Info

Logging

template<std::size_t level = 0>
struct info

template<std::size_t level = 0>
struct warn

template<std::size_t level = 0>
struct error

template<typename ...Args>
constexpr void roq::log::critical(format_str<Args...> const &fmt, Args&&... args)

template<typename ...Args>
constexpr void roq::log::fatal(format_str<Args...> const &fmt, Args&&... args)

template<std::size_t level = 0>
struct debug

template<std::size_t level = 0>
struct system_error

Print

struct print