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Flow 1.0.2
Flow project: Public API.
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Catch-all namespace for the Flow project: A collection of various production-quality modules written in modern C++17, originally by ygoldfel. More...
Namespaces | |
| namespace | async |
| Flow module containing tools enabling multi-threaded event loops operating under the asynchronous-task proactor pattern, by providing a streamlined API around boost.asio event loops with added advanced task- and thread-scheduling features. | |
| namespace | cfg |
| Flow module that facilitates configuring modules, such as applications and APIs, via statically and/or dynamically parsed sets of name/value pairs from config sources like files and command lines. | |
| namespace | error |
| Flow module that facilitates working with error codes and exceptions; essentially comprised of niceties on top boost.system's error facility. | |
| namespace | log |
| Flow module providing logging functionality. | |
| namespace | net_flow |
| Flow module containing the API and implementation of the Flow network protocol, a TCP-inspired stream protocol that uses UDP as underlying transport. | |
| namespace | perf |
| Flow module containing tools for profiling and optimization. | |
| namespace | util |
| Flow module containing miscellaneous general-use facilities that don't fit into any other Flow module. | |
Classes | |
| class | Function< Result(Args...)> |
Intended as the polymorphic function wrapper of choice for Flow, internally and externally; to be used instead of std::function or boost::function. More... | |
Typedefs | |
| using | uint8_t = unsigned char |
| Byte. Best way to represent a byte of binary data. This is 8 bits on all modern systems. | |
| using | int8_t = signed char |
Signed byte. Prefer to use uint8_t when representing binary data. This is 8 bits on all modern systems. | |
| using | Fine_clock = boost::chrono::high_resolution_clock |
Clock used for delicate time measurements, such that the now() method gets the current time relative to some unknown but constant epoch (reference point). More... | |
| using | Fine_time_pt = Fine_clock::time_point |
A high-res time point as returned by Fine_clock::now() and suitable for precise time math in general. | |
| using | Fine_duration = Fine_clock::duration |
A high-res time duration as computed from two Fine_time_pts. | |
| using | Error_code = boost::system::error_code |
Short-hand for a boost.system error code (which basically encapsulates an integer/enum error code and a pointer through which to obtain a statically stored message string); this is how Flow modules report errors to the user; and we humbly recommended all C++ code use the same techniques. More... | |
Enumerations | |
| enum class | Flow_log_component { S_END_SENTINEL } |
| The flow::log::Component payload enumeration comprising various log components used by Flow's own internal logging. More... | |
Variables | |
| const boost::unordered_multimap< Flow_log_component, std::string > | S_FLOW_LOG_COMPONENT_NAME_MAP |
| The map generated by flow::log macro magic that maps each enumerated value in flow::Flow_log_component to its string representation as used in log output and verbosity config. More... | |
Catch-all namespace for the Flow project: A collection of various production-quality modules written in modern C++17, originally by ygoldfel.
(The very first version was in Boost-y C++03, back around 2010. Later, ~2019, it moved to C++14 in style and substance; and in 2022 to C++17 – a relatively minor upgrade.) While the modules are orthogonal to each other in terms of functionality provided, they all share a common set of stylistic conventions and happen to use each other internally; hence they are distributed together as of this writing.
From the user's perspective, one should view this namespace as the "root," meaning it consists of two parts:
included/referenced without directly includeing/referring to the others. E.g., one can directly reference namespace log and/or namespace util and/or namespace net_flow and/or .... Further documentation can be found in the doc headers for each individual sub-namespace.flow: The absolute most basic, commonly used symbols (such as uint32_t or Error_code). There should be only a handful of these, and they are likely to be small.enum class Flow_log_component which defines the set of possible flow::log::Component values logged from within all modules of Flow (again, including flow::util, flow::async, flow::net_flow, etc.). See end of common.hpp.Reiterating: Non-namespace symbols directly inside namespace flow are to be only extremely ubiquitous items such as the basic integer types and the log component enum. Anything beyond that should go into a sub-namespace of flow; if it is something miscellaneous then put it into flow::util.
Here we summarize topics relevant to all of Flow. It is recommend one reads this before using any individual module, for topics like file organization and style conventions, topics arguably not of huge practical value right away. However, all the actual functionality is in the sub-modules, so once you're ready to actually do stuff, I reiterate: See the list of sub-namespaces of flow and start with the doc header of the one(s) of interest to you.
All code in the project proper follows a high standard of documentation, almost solely via comments therein (as opposed to ancillary doc files/READMEs/etc.). Additionally, a subset of comments are Doxygen-targeted, meaning the comment starts with a special character sequence to cause the Doxygen utility to treat that comment as a doc header for a nearby symbol (class, method, etc.). (If you're not familiar with Doxygen: It's like Javadoc but better – although mostly compatible with Javadoc-targeted comments as well – not that we care about that.)
From the same source code (the entire Flow tree) 2 (two) web docs are generated by Doxygen utility – depending on which of the 2 Doxygen configuration files is chosen. You can determine which web docs you're reading currently (if indeed you are doing that, as opposed to reading raw code) via the wording of the title/header in every web page:
"@internal" Doxygen command within each given Doxygen comment is ignored. Browsable source code is omitted. As a result, a clean public API documentation is generated with no "fat."While an important (achieved) goal is to keep the documentation of the library (internal and external, as noted) self-contained – within the source code or auto-generated by taking that source code as input – nevertheless some satellite documentation is likely to exist; for example to cover such things as the logistical state of the project, its test harness, perhaps the license, etc. Look outside the root src/flow directory.
"@author" (including contact info); GitHub/other address indicating where to browse the project source; link(s) to the latest auto-generated web docs (if any); a section on the history of the project; and licensing info (if deemed needed) or pointer to it. (Reminder: Also update any similar sections of the historically significant net_flow::Node doc header.)io module/namespace for general networking/local I/O. (Flow itself continued to be developed, but some features were added elsewhere for expediency; this is a reminder to factor them out into Flow for the benefit of all.) Some features to migrate here might be: boost.asio extensions to UDP receive APIs to obtain receipt time stamps and destination IP (recvmsg() with ancillary data extensions) and to receive multiple datagrams in one call (recvmmsg()); boost.asio-adjacent facility to add custom socket options similarly to how boost.asio does it internally; boost.asio support for (local) transmission of native socket handles and security data over stream sockets (SCM_RIGHTS, etc.).This section discusses usability topics that apply to all Flow modules including hopefully any future ones but definitely all existing ones as of this writing.
Similarly to boost.asio, all public methods that may return errors can either do so via an error code or an exception encapsulating that same error code. If user passes in non-null pointer to a flow::Error_code variable, the latter is set to success (falsy) or a specific failure (truthy enum value). If user passes in null pointer, an exception exc is thrown only in case of error and will encapsulate that error code (accessible via exc.code()).
For details about error reporting, see doc headers for flow::Error_code (spoiler alert: a mere alias to boost::system::error_code) and namespace flow::error.
The flow::log namespace (see especially log::Logger and the various FLOW_LOG_...*() macros in log/log.hpp) provides a logging facility – used by Flow modules' often-extensive logging, and equally available to the Flow user. Ultimately, you may tweak the log level and then observe the given Flow module's internal behavior to whatever level of detail you desire. Similarly, as the user, you may use this system for your own logging, even if you use no Flow module other than flow::log itself. Either way, you can hook up flow::log to log via your own log output device in arbitrary fashion (e.g., save the log messages in a database, if that's what you want).
For details about logging, see doc header for namespace flow::log.
| using flow::Error_code = typedef boost::system::error_code |
Short-hand for a boost.system error code (which basically encapsulates an integer/enum error code and a pointer through which to obtain a statically stored message string); this is how Flow modules report errors to the user; and we humbly recommended all C++ code use the same techniques.
Error_code's) ubiquity. Very few other symbols should follow suit. We may decide to move it there after all.All error-reporting Flow APIs follow the following pattern of error reporting semantics. Each API looks something like:
Then, there are two possibilities. If you pass in non-null err_code, then after return *err_code is success (falsy) or a truthy enum-like value, representing a specific error. If, instead, you pass in null, then a flow::error::Runtime_error() exc is thrown if and only if *err_code would have been set to truthy value e_c had a non-null err_code been passed in. If such an exception is thrown, Error_code e_c is encapsulated in exception object exc. If and only if no exception is thrown, there was no error (*err_code would have been falsy).
Thus, you get the best of both worlds: you can get the simplicity and performance of an error code; or the various features of an exception (including access to the error code via exc.code() if desired), with the same API signature. (boost.asio follows a similar concept, though it requires two API signatures for each operation, one without an Error_code argument, and one with non-const Error_code& out-arg. The above convention is more compact; plus we provide certain tools to reduce boiler-plate in connection with this.)
Error_code, a/k/a boost.system error_code(I am restating boost.system documentation here, but that particular set of docs is notoriously formal-but-reader-unfriendly.)
A truthy Error_code is a very lightweight – errno-like in that regard – value indicating the error that occurred. It stores an int code and a "category" pointer (basically, thing specifying to what code set this belongs). The int is to be converted from the error code set of choice, whereas the category pointer is internally magically determined based on the type of the error code value being converted to Error_code.
An Error_code itself can be serialized into ostreams (and thus strings via lexical_cast, etc.) easily for logging purposes/etc. You can access both the numeric code and a human explanation of the error. Any and all error code sets are supported by this boost.system type. POSIX errnos are one possible set of codes; boost.asio has its own code set; and other modules in flow may introduce their own code sets. All are compatible for equality/assignment/etc. with this general Error_code type.
As stated, all error-emitting Flow public APIs (regardless of module) use the above-described error-reporting conventions. In addition, we humbly recommend Flow user code adopt the same battle-tested conventions. However that is absolutely not required and is entirely independent of the fact that Flow modules use them. Do note this convention is battle-tested in boost.asio as well; though Flow's version is more compact; by using a pointer (which can be null) instead of a reference it cuts the number of error-emitting API functions in half.
For each function (including each publicly exported error-reporting function within Flow) that indeed agrees to use the above convention, follow these instructions:
To reduce boiler-plate, within reason, it is incumbent on each error-reporting method to use the following technique:
err_code) and use the above semantics.bool return value.The error behavior documentation should be confined entirely to the documentation of err_code parameter, so that the above semantics need not be repetitively restated a million times. The text of the parameter's doc should usually be as follows (you may copy/paste to start). In this example the function returns codes from the net_flow::error::Code code set enum; but please substitute your code set of choice (again; errno and boost.asio error codes are 2 possible other examples of code sets). Here we go:
namespace flow::net_flow::error is a good primer showing how to create an Error_code-compatible set of error codes. This is easier to understand than boost.asio's counterpart for example.Error_code* out-arg, throw if null. They, instead propose: Error_code& out-arg, throw if it equals boost::system::throws(). That's great, too, but actually our idiom hews to another bit of the Flow coding style/guide, wherein out-args should be pointers, not non-const references – and is otherwise very similar. So it's fine. Note that their idiom vs. ours = orthogonal to the main difficulty which is the boiler-plate associated with actually throwing vs. non-throwing; this would be required regardless of the API idiom chosen. The above (involving FLOW_ERROR_EXEC_AND_THROW_ON_ERROR(), etc.) is really the main crux of it. | using flow::Fine_clock = typedef boost::chrono::high_resolution_clock |
Clock used for delicate time measurements, such that the now() method gets the current time relative to some unknown but constant epoch (reference point).
Used to measure durations of things. It has the following properties:
So basically it's a precise clock with no surprises (which is more than can be said for stuff people tend to be forced to use, like gettimeofday()).
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strong |
The flow::log::Component payload enumeration comprising various log components used by Flow's own internal logging.
Internal Flow code specifies members thereof when indicating the log component for each particular piece of logging code. Flow user specifies it, albeit very rarely, when configuring their program's logging such as via flow::log::Config::init_component_to_union_idx_mapping() and flow::log::Config::init_component_names().
If you are reading this in Doxygen-generated output (likely a web page), be aware that the individual enum values are not documented right here, because flow::log auto-generates those via certain macro magic, and Doxygen cannot understand what is happening. However, you will find the same information directly in the source file log_component_enum_declare.macros.hpp (if the latter is clickable, click to see the source).
The following is a less formal reiteration of flow::log::Config documentation and is presented here – even though technically in the present context Flow itself is nothing more than yet another module that uses flow::log for its own logging – for your convenience. Flow's own logging can be seen as the canonical/model use of flow::log, so other flow::log users can read this to learn the basics of how to configure loggingg. That's why we re-explain this info here, in brief form:
Your program – that uses the present library – can register this enum in order for these components (and particularly the log messages that specify them via flow::log::Log_context or FLOW_LOG_SET_CONTEXT()) to be logged properly in that program, co-existing correctly with other code bases that use flow::log for logging. Typically one constructs a flow::log::Config C and then at some point before logging begins:
enum class X_log_component (note that Flow_log_component is only one such enum class):C.init_component_to_union_idx_mapping<X_log_component>(K), where K is a distinct numeric offset, maybe multiple of 1000.C.init_component_names<X_log_component>(S_X_LOG_COMPONENT_NAME_MAP, ..., "X-").C.configure_default_verbosity(Sev::S), where S is some default max severity.M for which one desires a different max severity S:C.configure_component_verbosity<X_log_component>(Sev::S, X_log_component::M). OR:C.configure_component_verbosity_by_name(Sev::S, "X-M").C to the flow::log::Logger or Loggers you want to affect.Logger or Loggers to appropriate APIs that want to log.One could make changes after logging has begun, but that's a separate topic.
| Enumerator | |
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| S_END_SENTINEL | CAUTION – see flow::Flow_log_component doc header for directions to find actual members of this This entry is a placeholder for Doxygen purposes only, because of the macro magic involved in generating the actual |
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extern |
The map generated by flow::log macro magic that maps each enumerated value in flow::Flow_log_component to its string representation as used in log output and verbosity config.
Flow user specifies, albeit very rarely, when configuring their program's logging via flow::log::Config::init_component_names().
As a Flow user, you can informally assume that if the component enum member is called S_SOME_NAME, then its string counterpart in this map will be auto-computed to be "SOME_NAME" (optionally prepended with a prefix as supplied to flow::log::Config::init_component_names()). This is achieved via flow::log macro magic.
1.9.4