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Developer Notes

Table of Contents

Coding Style (General)

Various coding styles have been used during the history of the codebase, and the result is not very consistent. However, we're now trying to converge to a single style, which is specified below. The following guidelines apply:

  • New code and new modules should follow the style guide below.
  • Modifying legacy code: be consistent with the surrounding scope. Avoid gratuitous style churn in otherwise focused patches.
  • Don't mix cosmetic/style changes with domain changes in the same commit. If style cleanup is needed, do it in a separate commit (scripted-diff is preferred for large-scale reformatting).
  • New scopes within legacy code (e.g. a new function in an old file) may follow the style guide.
  • Upstream (subtree) code should not have its style modified in-tree. Send style changes upstream.

Coding Style (C++)

  • Indentation and whitespace rules as specified in src/.clang-format. You can use the provided clang-format-diff script tool to clean up patches automatically before submission.

    • Braces on new lines for classes, functions, methods.
    • Braces on the same line for everything else.
    • 4 space indentation (no tabs) for every block except namespaces.
    • No indentation for public/protected/private or for namespace.
    • No extra spaces inside parenthesis; don't do ( this ).
    • No space after function names; one space after if, for and while.
    • If an if only has a single-statement then-clause, it can appear on the same line as the if, without braces. In every other case, braces are required, and the then and else clauses must appear correctly indented on a new line.
    • There's no hard limit on line width, but prefer to keep lines to <100 characters if doing so does not decrease readability. Break up long function declarations over multiple lines using the Clang Format AlignAfterOpenBracket style option.

  • Symbol naming conventions. These are preferred in new code, but are not required when doing so would need changes to significant pieces of existing code.

    • Variable (including function arguments) and namespace names are all lowercase and may use _ to separate words (snake_case).

      • Class member variables have a m_ prefix.
      • Global variables have a g_ prefix.

    • Compile-time constant names are all uppercase, and use _ to separate words.

    • Class names, function names, and method names are UpperCamelCase (PascalCase). Do not prefix class names with C.

    • Test suite naming convention: The Boost test suite in file src/test/foo_tests.cpp should be named foo_tests. Test suite names must be unique.

    • Legacy conventions: Older code uses Hungarian notation for variable names (nCount, strName, fEnabled, vItems, mapEntries, pPointer) and the C class prefix (CBlock, CWallet). The modern conventions above (snake_case, m_ prefix, no C prefix) are preferred for new code, but existing conventions should be respected per the general style guidance above.

  • Miscellaneous

    • ++i is preferred over i++.
    • nullptr is preferred over NULL or (void*)0.
    • static_assert is preferred over assert where possible. Generally; compile-time checking is preferred over run-time checking.

Block style example:

int g_count = 0;

namespace foo {
class Class
{
    std::string m_name;

public:
    bool Function(const std::string& s, int n)
    {
        // Comment summarising what this section of code does
        for (int i = 0; i < n; ++i) {
            int total_sum = 0;
            // When something fails, return early
            if (!Something()) return false;
            ...
            if (SomethingElse(i)) {
                total_sum += ComputeSomething(g_count);
            } else {
                DoSomething(m_name, total_sum);
            }
        }

        // Success return is usually at the end
        return true;
    }
}
} // namespace foo

Coding Style (Python)

Adhere to PEP8.

Coding Style (Doxygen-compatible comments)

Gridcoin Core uses Doxygen to generate its official documentation.

Use Doxygen-compatible comment blocks for functions, methods, and fields.

For example, to describe a function use:

/**
 * ... Description ...
 *
 * @param[in]  arg1 input description...
 * @param[in]  arg2 input description...
 * @param[out] arg3 output description...
 * @return Return cases...
 * @throws Error type and cases...
 * @pre  Pre-condition for function...
 * @post Post-condition for function...
 */
bool function(int arg1, const char *arg2, std::string& arg3)

A complete list of @xxx commands can be found at https://www.doxygen.nl/manual/commands.html. As Doxygen recognizes the comments by the delimiters (/** and */ in this case), you don't need to provide any commands for a comment to be valid; just a description text is fine.

To describe a class, use the same construct above the class definition:

/**
 * Alerts are for notifying old versions if they become too obsolete and
 * need to upgrade. The message is displayed in the status bar.
 * @see GetWarnings()
 */
class CAlert

To describe a member or variable use:

//! Description before the member
int var;

or

int var; //!< Description after the member

Also OK:

///
/// ... Description ...
///
bool function2(int arg1, const char *arg2)

Not picked up by Doxygen:

//
// ... Description ...
//

Also not picked up by Doxygen:

/*
 * ... Description ...
 */

A full list of comment syntaxes picked up by Doxygen can be found at https://www.doxygen.nl/manual/docblocks.html, but the above styles are favored.

Recommendations:

  • Avoiding duplicating type and input/output information in function descriptions.

  • Use backticks (``) to refer to argument names in function and parameter descriptions.

  • Backticks aren't required when referring to functions Doxygen already knows about; it will build hyperlinks for these automatically. See https://www.doxygen.nl/manual/autolink.html for complete info.

  • Avoid linking to external documentation; links can break.

  • Javadoc and all valid Doxygen comments are stripped from Doxygen source code previews (STRIP_CODE_COMMENTS = YES in Doxyfile.in). If you want a comment to be preserved, it must instead use // or /* */.

Generating Documentation

The documentation can be generated with CMake:

cmake -B build -DENABLE_DOCS=ON
cmake --build build --target docs
# Output: build/doc/doxygen/html/index.html

Before building the docs, you'll need to install these dependencies:

Linux: sudo apt install doxygen graphviz

MacOS: brew install doxygen graphviz

Development tips and tricks

Compiling for debugging

Configure with -DCMAKE_BUILD_TYPE=Debug to produce debugging builds:

cmake -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build -j $(nproc)

Note: The default build type RelWithDebInfo provides debug symbols with optimizations enabled, which is sufficient for most debugging with gdb.

Compiling for gprof profiling

gprof is not currently supported as a dedicated option in the CMake build system. Use perf instead (see Performance profiling with perf below), which is the preferred modern approach and does not require recompilation.

debug.log

If the code is behaving strangely, take a look in the debug.log file in the data directory. Error and debugging messages are written there.

The -debug=<category> command-line option controls debugging. Multiple options can be specified. While running the application, logging can be dynamically changed with the logging rpc call. -debug=VERBOSE corresponds to the most common needs for debugging, while -debug=NOISY results in extensive debugging entries.

The Qt code routes qDebug() output to debug.log under category "qt": run with -debug=qt to see it.

Testnet mode

If you are testing multi-machine code that needs to operate across the internet, you can run with the -testnet config option to test with "play Gridcoins" on the test network. Specify org=<identifier> in your config file when using testnet so that your nodes can be identified.

DEBUG_LOCKORDER

Gridcoin is a multi-threaded application, and deadlocks or other multi-threading bugs can be very difficult to track down. Building with -DENABLE_DEBUG_LOCKORDER=ON adds -DDEBUG_LOCKORDER to the compiler flags. This inserts run-time checks to keep track of which locks are held and adds warnings to the debug.log file if inconsistencies are detected. This option is independent of CMAKE_BUILD_TYPE so it can be used with any build configuration.

Assertions and Checks

The util file src/util/check.h offers helpers to protect against coding and internal logic bugs. They must never be used to validate user, network or any other input.

  • assert or Assert should be used to document assumptions when any violation would mean that it is not safe to continue program execution. The code is always compiled with assertions enabled.
    • For example, a nullptr dereference or any other logic bug in validation code means the program code is faulty and must terminate immediately.
  • CHECK_NONFATAL should be used for recoverable internal logic bugs. On failure, it will throw an exception, which can be caught to recover from the error.
    • For example, a nullptr dereference or any other logic bug in RPC code means that the RPC code is faulty and can not be executed. However, the logic bug can be shown to the user and the program can continue to run.
  • Assume should be used to document assumptions when program execution can safely continue even if the assumption is violated. In debug builds it behaves like Assert/assert to notify developers and testers about nonfatal errors. In production it doesn't warn or log anything, though the expression is always evaluated.
    • For example it can be assumed that a variable is only initialized once, but a failed assumption does not result in a fatal bug. A failed assumption may or may not result in a slightly degraded user experience, but it is safe to continue program execution.

Valgrind suppressions file

Valgrind is a programming tool for memory debugging, memory leak detection, and profiling. The repo contains a Valgrind suppressions file (valgrind.supp) which includes known Valgrind warnings in our dependencies that cannot be fixed in-tree. Example use:

$ valgrind --suppressions=contrib/valgrind.supp build/src/test/test_gridcoin
$ valgrind --suppressions=contrib/valgrind.supp --leak-check=full \
      --show-leak-kinds=all build/src/test/test_gridcoin --log_level=test_suite
$ valgrind -v --leak-check=full build/src/gridcoinresearchd -printtoconsole

Compiling for test coverage

Dedicated lcov/coverage support is not yet integrated into the CMake build system. See doc/cmake-options.md for current build options. In the meantime, coverage can be achieved manually by adding --coverage to CMAKE_CXX_FLAGS and CMAKE_EXE_LINKER_FLAGS:

cmake -B build_cov \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_CXX_FLAGS="--coverage" \
  -DCMAKE_EXE_LINKER_FLAGS="--coverage"
cmake --build build_cov -j $(nproc)
ctest --test-dir build_cov --output-on-failure

# Generate report with lcov (install the `lcov` package on Debian/Ubuntu):
lcov --capture --directory build_cov --output-file coverage.info
genhtml coverage.info --output-directory coverage_report
# Open coverage_report/index.html to view.

Performance profiling with perf

Profiling is a good way to get a precise idea of where time is being spent in code. One tool for doing profiling on Linux platforms is called perf. Perf can observe a running process and sample (at some frequency) where its execution is.

Perf installation is contingent on which kernel version you're running; see this thread for specific instructions.

Certain kernel parameters may need to be set for perf to be able to inspect the running process's stack.

$ sudo sysctl -w kernel.perf_event_paranoid=-1
$ sudo sysctl -w kernel.kptr_restrict=0

Make sure you understand the security trade-offs of setting these kernel parameters.

To profile a running gridcoinresearchd process for 60 seconds, you could use an invocation of perf record like this:

$ perf record \
    -g --call-graph dwarf --per-thread -F 140 \
    -p `pgrep gridcoinresearchd` -- sleep 60

You could then analyze the results by running:

perf report --stdio | c++filt | less

or using a graphical tool like Hotspot.

To profile specific tests or other commands, run them under perf record using similar options to those shown above.

Stopwatch timing with MilliTimer

For measuring elapsed time within the application itself, Gridcoin provides the MilliTimer class (src/util/time.h). It implements a thread-safe stopwatch-style timer with "lap time" support, useful for profiling code paths that span multiple functions or stages. A global instance g_timer is available throughout the codebase.

Key methods:

  • InitTimer(label, log) — Start a new named timer. If log is true, lap times are written to debug.log automatically.
  • GetTimes(log_string, label) — Return a timer struct with elapsed_time (since init) and time_since_last_check (since last call). If logging is enabled, emits the times to debug.log prefixed with log_string.
  • GetElapsedTime(log_string, label) — Convenience wrapper returning only the elapsed time.
  • DeleteTimer(label) — Remove a timer from the map.

Example — timing stages of the miner loop:

#include <util/time.h>

extern MilliTimer g_timer;

void ThreadStakeMiner(...)
{
    std::string function = __func__ + std::string(": ");

    // Init the "miner" timer; enable logging if MISC category is active
    g_timer.InitTimer("miner", LogInstance().WillLogCategory(BCLog::LogFlags::MISC));

    // ... do work ...
    g_timer.GetTimes(function + "SelectCoinsForStaking", "miner");

    // ... do more work ...
    g_timer.GetTimes(function + "CreateCoinStake", "miner");

    // ... etc ...
    g_timer.GetTimes(function + "ProcessBlock", "miner");
}

With logging enabled, each GetTimes call emits a line like:

INFO: GetTimes: timer miner: ThreadStakeMiner: CreateCoinStake: elapsed time: 1234 ms, time since last check: 56 ms.

The g_timer instance is also used during initialization (src/init.cpp) to measure startup phases. For simple single-point timings, using GetTimeMillis() directly is lighter weight than constructing a MilliTimer.

Sanitizers

Gridcoin Core can be compiled with various "sanitizers" enabled, which add instrumentation for issues regarding things like memory safety, thread race conditions, or undefined behavior. These sanitizers have runtime overhead, so they are most useful when testing changes or producing debugging builds. Sanitizers are actively used in CI (see .github/workflows/cmake_quality.yml).

To build with AddressSanitizer (ASan) and UndefinedBehaviorSanitizer (UBSan), pass the flags via CMAKE_CXX_FLAGS and CMAKE_EXE_LINKER_FLAGS:

cmake -B build_asan \
  -DCMAKE_BUILD_TYPE=Debug \
  -DUSE_ASM=OFF \
  -DCMAKE_CXX_FLAGS="-fsanitize=address,undefined -fno-omit-frame-pointer" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address,undefined"
cmake --build build_asan -j $(nproc)

# Run tests with suppression files:
LSAN_OPTIONS=suppressions=test/sanitizer_suppressions/lsan \
UBSAN_OPTIONS=suppressions=test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1 \
ASAN_OPTIONS=malloc_context_size=0:check_initialization_order=1 \
  ctest --test-dir build_asan --output-on-failure

To build with ThreadSanitizer (TSan) instead:

cmake -B build_tsan \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_CXX_FLAGS="-fsanitize=thread" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=thread"
cmake --build build_tsan -j $(nproc)

TSAN_OPTIONS=suppressions=test/sanitizer_suppressions/tsan \
  ctest --test-dir build_tsan --output-on-failure

Suppression files for known issues in dependencies are located in test/sanitizer_suppressions/ (lsan, tsan, ubsan).

Notes:

  • -DUSE_ASM=OFF is recommended when using ASan, as the hand-written assembly can produce false positives. This also disables USE_ASM_SCRYPT (scrypt assembly). See doc/cmake-options.md for details on these flags.
  • If you are compiling with GCC you will typically need to install corresponding "san" libraries, e.g. libasan for ASan, libtsan for TSan, and libubsan for UBSan.
  • ASan and TSan are mutually incompatible and cannot be enabled at the same time. Refer to your compiler manual for details.

Additional resources:

Locking/mutex usage notes

The code is multi-threaded and uses mutexes and the LOCK and TRY_LOCK macros to protect data structures.

Deadlocks due to inconsistent lock ordering (thread 1 locks cs_main and then cs_wallet, while thread 2 locks them in the opposite order: result, deadlock as each waits for the other to release its lock) are a problem. Compile with -DENABLE_DEBUG_LOCKORDER=ON to get lock order inconsistencies reported in the debug.log file.

Lock macros

  • LOCK(cs) — Acquires a single lock.
  • LOCK2(cs1, cs2) — Acquires two locks sequentially in argument order (cs1 first, then cs2). Bitcoin Core later reimplemented LOCK2 using std::lock() to provide deadlock avoidance regardless of argument order. This codebase does not use that approach — LOCK2 is simply two sequential lock acquisitions. This means argument order matters: callers must list locks in the canonical order to prevent deadlocks. For example, always write LOCK2(cs_main, cs_wallet), never LOCK2(cs_wallet, cs_main).
  • TRY_LOCK(cs, name) — Non-blocking lock attempt.

Canonical lock ordering

When multiple locks must be held simultaneously, acquire them in the following order to prevent deadlocks:

  1. cs_main (blockchain state)
  2. cs_wallet (wallet operations)
  3. Subsystem-specific locks (e.g. cs_poll_registry, cs_ScraperGlobals)

This ordering applies regardless of whether you use LOCK2 or separate LOCK statements. The DEBUG_LOCKORDER build flag will detect violations at runtime and report them in debug.log.

Reading DEBUG_LOCKORDER output

When a lock ordering violation is detected, the output looks like this:

POTENTIAL DEADLOCK DETECTED
Conflict: 'cs_main' and 'cs_poll_registry' acquired in inconsistent orders.
  Current:    'cs_main' -> 'cs_poll_registry'
  Historical: 'cs_poll_registry' -> 'cs_main'

Historical lock stack (where the reverse order was first seen):
  #1 'cs_main' in src/main.cpp:200 (in thread 'main')  <--
  #2 'cs_poll_registry' in src/gridcoin/voting/registry.cpp:1057 (in thread 'main')  <--
  #3 'cs_main' in src/main.cpp:736 (in thread 'main')  (re-entrant, already held above)

Current lock stack (triggering this warning):
  #1 'cs_main' in src/gridcoin/gridcoin.cpp:636 (in thread '')  <--
  #2 'cs_poll_registry' in src/gridcoin/gridcoin.cpp:636 (in thread '')  <--

Key elements:

  • Conflict summary: Names both locks and shows the two orderings that conflict.
  • Stack entries: Numbered by acquisition order. <-- marks the first occurrence of each conflicting lock.
  • Re-entrant flag: When a lock appears as "already held above", the apparent inversion may be a false positive — the lock was already held higher in the stack, so the re-acquisition is harmless. This is common with CCriticalSection (recursive mutex) when a function that takes LOCK(cs_main) is called from code that already holds cs_main.

Re-architecting the core code so there are better-defined interfaces between the various components is a goal, with any necessary locking done by the components (e.g. see the self-contained CKeyStore class (in src/keystore.h) and its cs_KeyStore lock for example).

Threads

Gridcoin is a multi-threaded application. Key threads include:

Thread Source Description
ThreadStakeMiner src/net.cpp Proof-of-stake block creation (calls StakeMiner() in src/miner.cpp)
ThreadScraper src/gridcoin/gridcoin.cpp Active scraper: downloads BOINC project stats and publishes signed manifests (mutually exclusive with subscriber)
ThreadScraperSubscriber src/gridcoin/gridcoin.cpp Subscriber: receives scraper manifests and runs convergence to build superblocks (mutually exclusive with scraper)
ThreadSocketHandler src/net.cpp Low-level socket I/O for P2P connections
ThreadMessageHandler src/net.cpp Processes incoming P2P messages
ThreadOpenConnections src/net.cpp Manages outbound peer connections
ThreadDNSAddressSeed src/net.cpp Resolves DNS seeds to bootstrap peer discovery
ThreadDumpAddress src/net.cpp Periodically dumps known peer addresses to peers.dat
RPC threads src/rpc/server.cpp Thread pool serving JSON-RPC requests
Scheduler src/scheduler.cpp Runs deferred and periodic tasks

Ignoring IDE/editor files

In closed-source environments in which everyone uses the same IDE, it is common to add temporary files it produces to the project-wide .gitignore file.

However, in open source software such as Gridcoin Core, where everyone uses their own editors/IDE/tools, it is less common. Only you know what files your editor produces and this may change from version to version. The canonical way to do this is thus to create your local gitignore. Add this to ~/.gitconfig:

[core]
        excludesfile = /home/.../.gitignore_global

(alternatively, type the command git config --global core.excludesfile ~/.gitignore_global on a terminal)

Then put your favourite tool's temporary filenames in that file, e.g.

# NetBeans
nbproject/

Another option is to create a per-repository excludes file .git/info/exclude. These are not committed but apply only to one repository.

If a set of tools is used by the build system or scripts in the repository (for example, lcov) it is perfectly acceptable to add its files to .gitignore and commit them.

Development guidelines

A few non-style-related recommendations for developers, as well as points to pay attention to for reviewers of Gridcoin Core code.

General Gridcoin Core

  • New features should be exposed on RPC first, then can be made available in the GUI.

    • Rationale: RPC allows for better automatic testing. The test suite for the GUI is very limited.

  • Make sure pull requests pass CI before merging.

    • Rationale: Makes sure that they pass thorough testing, and that the tester will keep passing on the master branch. Otherwise, all new pull requests will start failing the tests, resulting in confusion and mayhem.

    • Explanation: If the test suite is to be updated for a change, this has to be done first.

Wallet

  • Make sure that no crashes happen with run-time option -disablewallet.

  • Include db_cxx.h (BerkeleyDB header) only when ENABLE_WALLET is set.

    • Rationale: Otherwise compilation of the disable-wallet build will fail in environments without BerkeleyDB.

General C++

For general C++ guidelines, you may refer to the C++ Core Guidelines.

Common misconceptions are clarified in those sections:

  • Passing (non-)fundamental types in the C++ Core Guideline.

  • Assertions should not have side-effects.

    • Rationale: Even though the source code is set to refuse to compile with assertions disabled, having side-effects in assertions is unexpected and makes the code harder to understand.

  • If you use the .h, you must link the .cpp.

    • Rationale: Include files define the interface for the code in implementation files. Including one but not linking the other is confusing. Please avoid that. Moving functions from the .h to the .cpp should not result in build errors.

  • Use the RAII (Resource Acquisition Is Initialization) paradigm where possible. For example, by using unique_ptr for allocations in a function.

    • Rationale: This avoids memory and resource leaks, and ensures exception safety.

C++ data structures

  • Never use the std::map [] syntax when reading from a map, but instead use .find().

    • Rationale: [] does an insert (of the default element) if the item doesn't exist in the map yet. This has resulted in memory leaks in the past, as well as race conditions (expecting read-read behavior). Using [] is fine for writing to a map.

  • Do not compare an iterator from one data structure with an iterator of another data structure (even if of the same type).

    • Rationale: Behavior is undefined. In C++ parlor this means "may reformat the universe", in practice this has resulted in at least one hard-to-debug crash bug.

  • Watch out for out-of-bounds vector access. &vch[vch.size()] is illegal, including &vch[0] for an empty vector. Use vch.data() and vch.data() + vch.size() instead.

  • Vector bounds checking is only enabled in debug mode. Do not rely on it.

  • Initialize all non-static class members where they are defined. If this is skipped for a good reason (i.e., optimization on the critical path), add an explicit comment about this.

    • Rationale: Ensure determinism by avoiding accidental use of uninitialized values. Also, static analyzers balk about this. Initializing the members in the declaration makes it easy to spot uninitialized ones.
class A
{
    uint32_t m_count{0};
}

  • By default, declare constructors explicit.

    • Rationale: This is a precaution to avoid unintended conversions.

  • Use explicitly signed or unsigned chars, or even better uint8_t and int8_t. Do not use bare char unless it is to pass to a third-party API. This type can be signed or unsigned depending on the architecture, which can lead to interoperability problems or dangerous conditions such as out-of-bounds array accesses.

  • Prefer explicit constructions over implicit ones that rely on 'magical' C++ behavior.

    • Rationale: Easier to understand what is happening, thus easier to spot mistakes, even for those that are not language lawyers.

  • Use Span as function argument when it can operate on any range-like container.

    • Rationale: Compared to Foo(const vector<int>&) this avoids the need for a (potentially expensive) conversion to vector if the caller happens to have the input stored in another type of container. However, be aware of the pitfalls documented in span.h.
void Foo(Span<const int> data);

std::vector<int> vec{1,2,3};
Foo(vec);

  • Prefer enum class (scoped enumerations) over enum (traditional enumerations) where possible.

    • Rationale: Scoped enumerations avoid two potential pitfalls/problems with traditional C++ enumerations: implicit conversions to int, and name clashes due to enumerators being exported to the surrounding scope.

  • switch statement on an enumeration example:

enum class Tabs {
    INFO,
    CONSOLE,
    GRAPH,
    PEERS
};

int GetInt(Tabs tab)
{
    switch (tab) {
    case Tabs::INFO: return 0;
    case Tabs::CONSOLE: return 1;
    case Tabs::GRAPH: return 2;
    case Tabs::PEERS: return 3;
    } // no default case, so the compiler can warn about missing cases
    assert(false);
}

Rationale: The comment documents skipping default: label, and it complies with clang-format rules. The assertion prevents firing of -Wreturn-type warning on some compilers.

Strings and formatting

  • Be careful of LogPrint versus LogPrintf. LogPrint takes a category argument, LogPrintf does not.

    • Rationale: Confusion of these can result in runtime exceptions due to formatting mismatch, and it is easy to get wrong because of subtly similar naming.

  • Use std::string, avoid C string manipulation functions.

    • Rationale: C++ string handling is marginally safer, less scope for buffer overflows, and surprises with \0 characters. Also, some C string manipulations tend to act differently depending on platform, or even the user locale.

  • Use ParseInt32, ParseInt64, ParseUInt32, ParseUInt64, ParseDouble from util/strencodings.h for number parsing.

    • Rationale: These functions do overflow checking and avoid pesky locale issues.

  • Avoid using locale dependent functions if possible. You can use the provided lint-locale-dependence.sh to check for accidental use of locale dependent functions.

    • Rationale: Unnecessary locale dependence can cause bugs that are very tricky to isolate and fix.

    • These functions are known to be locale dependent: alphasort, asctime, asprintf, atof, atoi, atol, atoll, atoq, btowc, ctime, dprintf, fgetwc, fgetws, fprintf, fputwc, fputws, fscanf, fwprintf, getdate, getwc, getwchar, isalnum, isalpha, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, iswalnum, iswalpha, iswblank, iswcntrl, iswctype, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, isxdigit, mblen, mbrlen, mbrtowc, mbsinit, mbsnrtowcs, mbsrtowcs, mbstowcs, mbtowc, mktime, putwc, putwchar, scanf, snprintf, sprintf, sscanf, stoi, stol, stoll, strcasecmp, strcasestr, strcoll, strfmon, strftime, strncasecmp, strptime, strtod, strtof, strtoimax, strtol, strtold, strtoll, strtoq, strtoul, strtoull, strtoumax, strtouq, strxfrm, swprintf, tolower, toupper, towctrans, towlower, towupper, ungetwc, vasprintf, vdprintf, versionsort, vfprintf, vfscanf, vfwprintf, vprintf, vscanf, vsnprintf, vsprintf, vsscanf, vswprintf, vwprintf, wcrtomb, wcscasecmp, wcscoll, wcsftime, wcsncasecmp, wcsnrtombs, wcsrtombs, wcstod, wcstof, wcstoimax, wcstol, wcstold, wcstoll, wcstombs, wcstoul, wcstoull, wcstoumax, wcswidth, wcsxfrm, wctob, wctomb, wctrans, wctype, wcwidth, wprintf

  • For strprintf, LogPrint, LogPrintf formatting characters don't need size specifiers.

    • Rationale: Gridcoin Core uses tinyformat, which is type safe. Leave them out to avoid confusion.

  • Use .c_str() sparingly. Its only valid use is to pass C++ strings to C functions that take NULL-terminated strings.

    • Do not use it when passing a sized array (so along with .size()). Use .data() instead to get a pointer to the raw data.

      • Rationale: Although this is guaranteed to be safe starting with C++11, .data() communicates the intent better.

    • Do not use it when passing strings to tfm::format, strprintf, LogPrint[f].

      • Rationale: This is redundant. Tinyformat handles strings.

    • Do not use it to convert to QString. Use QString::fromStdString().

      • Rationale: Qt has built-in functionality for converting their string type from/to C++. No need to roll your own.

    • In cases where do you call .c_str(), you might want to additionally check that the string does not contain embedded '\0' characters, because it will (necessarily) truncate the string. This might be used to hide parts of the string from logging or to circumvent checks. If a use of strings is sensitive to this, take care to check the string for embedded NULL characters first and reject it if there are any (see ParsePrechecks in strencodings.cpp for an example).

Shadowing

Although the shadowing warning (-Wshadow) is not enabled by default (it prevents issues arising from using a different variable with the same name), please name variables so that their names do not shadow variables defined in the source code.

When using nested cycles, do not name the inner cycle variable the same as in the upper cycle, etc.

Threads and synchronization

  • Prefer Mutex type to RecursiveMutex one

  • Consistently use Clang Thread Safety Analysis annotations to get compile-time warnings about potential race conditions in code. Combine annotations in function declarations with run-time asserts in function definitions:

    • In functions that are declared separately from where they are defined, the thread safety annotations should be added exclusively to the function declaration. Annotations on the definition could lead to false positives (lack of compile failure) at call sites between the two.
// miner.h
bool CreateGridcoinReward(CBlock& blocknew,
                          CBlockIndex* pindexPrev,
                          int64_t& nReward,
                          GRC::Claim& claim) EXCLUSIVE_LOCKS_REQUIRED(cs_main);

// miner.cpp
bool CreateGridcoinReward(CBlock& blocknew,
                          CBlockIndex* pindexPrev,
                          int64_t& nReward,
                          GRC::Claim& claim)
{
    AssertLockHeld(cs_main);
    ...
}
// Example: a function that acquires cs_main internally
// main.h
bool GetTransaction(const uint256& hash, CTransaction& tx, uint256& hashBlock);

// main.cpp
bool GetTransaction(const uint256& hash, CTransaction& tx, uint256& hashBlock)
{
    LOCK(cs_main);
    ...
}

  • Build and run tests with -DENABLE_DEBUG_LOCKORDER=ON to verify that no potential deadlocks are introduced.

  • When using LOCK/TRY_LOCK be aware that the lock exists in the context of the current scope, so surround the statement and the code that needs the lock with braces.

    OK:

{
    TRY_LOCK(cs_vNodes, lockNodes);
    ...
}

Wrong:

TRY_LOCK(cs_vNodes, lockNodes);
{
    ...
}

Scripts

Shebang

  • Use #!/usr/bin/env bash instead of obsolete #!/bin/bash.

    • Rationale:

      #!/bin/bash assumes it is always installed to /bin/ which can cause issues;

      #!/usr/bin/env bash searches the user's PATH to find the bash binary.

    OK:

#!/usr/bin/env bash

Wrong:

#!/bin/bash

Source code organization

  • Implementation code should go into the .cpp file and not the .h, unless necessary due to template usage or when performance due to inlining is critical.

    • Rationale: Shorter and simpler header files are easier to read and reduce compile time.

  • Use only the lowercase alphanumerics (a-z0-9), underscore (_) and hyphen (-) in source code filenames.

    • Rationale: grep:ing and auto-completing filenames is easier when using a consistent naming pattern. Potential problems when building on case- insensitive filesystems are avoided when using only lowercase characters in source code filenames.

  • Every .cpp and .h file should #include every header file it directly uses classes, functions or other definitions from, even if those headers are already included indirectly through other headers.

    • Rationale: Excluding headers because they are already indirectly included results in compilation failures when those indirect dependencies change. Furthermore, it obscures what the real code dependencies are.

  • Don't import anything into the global namespace (using namespace ...). Use fully specified types such as std::string.

    • Rationale: Avoids symbol conflicts.

  • Terminate namespaces with a comment (// namespace mynamespace). The comment should be placed on the same line as the brace closing the namespace, e.g.

namespace mynamespace {
...
} // namespace mynamespace

namespace {
...
} // namespace

  • Rationale: Avoids confusion about the namespace context.

  • Use #include <primitives/transaction.h> bracket syntax instead of #include "primitives/transactions.h" quote syntax.

    • Rationale: Bracket syntax is less ambiguous because the preprocessor searches a fixed list of include directories without taking location of the source file into account. This allows quoted includes to stand out more when the location of the source file actually is relevant.

  • Use include guards to avoid the problem of double inclusion. Two conventions are in use:

    • Bitcoin-inherited headers retain the BITCOIN_ prefix for upstream compatibility: foo/bar.h uses BITCOIN_FOO_BAR_H.
    • Gridcoin-specific headers use the GRIDCOIN_ prefix: gridcoin/foo.h uses GRIDCOIN_FOO_H.
#ifndef GRIDCOIN_FOO_H
#define GRIDCOIN_FOO_H
...
#endif // GRIDCOIN_FOO_H

GUI

  • Do not display or manipulate dialogs in model code (classes *Model).

    • Rationale: Model classes pass through events and data from the core, they should not interact with the user. That's where View classes come in. The converse also holds: try to not directly access core data structures from Views.

  • Avoid adding slow or blocking code in the GUI thread.

    Prefer to offload work from the GUI thread to worker threads (see RPCExecutor in console code as an example) or take other steps (see https://doc.qt.io/archives/qq/qq27-responsive-guis.html) to keep the GUI responsive.

    • Rationale: Blocking the GUI thread can increase latency, and lead to hangs and deadlocks.

Subtrees

Several parts of the repository are subtrees of software maintained elsewhere.

Some of these are maintained by active developers of Gridcoin Core, in which case changes should probably go directly upstream without being PRed directly against the project. They will be merged back in the next subtree merge.

Others are external projects without a tight relationship with our project. Changes to these should also be sent upstream, but bugfixes may also be prudent to PR against Gridcoin Core so that they can be integrated quickly. Cosmetic changes should be purely taken upstream.

There is a tool in test/lint/git-subtree-check.sh (instructions) to check a subtree directory for consistency with its upstream repository.

Current subtrees include:

Upgrading LevelDB

Extra care must be taken when upgrading LevelDB. This section explains issues you must be aware of.

File Descriptor Counts

In most configurations, we use the default LevelDB value for max_open_files, which is 1000 at the time of this writing. If LevelDB actually uses this many file descriptors, it will cause problems with Gridcoin's select() loop, because it may cause new sockets to be created where the fd value is >= 1024. For this reason, on 64-bit Unix systems, we rely on an internal LevelDB optimization that uses mmap() + close() to open table files without actually retaining references to the table file descriptors. If you are upgrading LevelDB, you must sanity check the changes to make sure that this assumption remains valid.

In addition to reviewing the upstream changes in env_posix.cc, you can use lsof to check this. For example, on Linux this command will show open .ldb file counts:

$ lsof -p $(pidof gridcoinresearchd) |\
    awk 'BEGIN { fd=0; mem=0; } /ldb$/ { if ($4 == "mem") mem++; else fd++ } END { printf "mem = %s, fd = %s\n", mem, fd}'
mem = 119, fd = 0

The mem value shows how many files are mmap'ed, and the fd value shows you many file descriptors these files are using. You should check that fd is a small number (usually 0 on 64-bit hosts).

Consensus Compatibility

It is possible for LevelDB changes to inadvertently change consensus compatibility between nodes. When upgrading LevelDB, you should review the upstream changes to check for issues affecting consensus compatibility.

For example, if LevelDB had a bug that accidentally prevented a key from being returned in an edge case, and that bug was fixed upstream, the bug "fix" would be an incompatible consensus change. In this situation, the correct behavior would be to revert the upstream fix before applying the updates to Gridcoin's copy of LevelDB. In general, you should be wary of any upstream changes affecting what data is returned from LevelDB queries.

Scripted diffs

For reformatting and refactoring commits where the changes can be easily automated using a bash script, we use scripted-diff commits. The bash script is included in the commit message and our CI job checks that the result of the script is identical to the commit. This aids reviewers since they can verify that the script does exactly what it is supposed to do. It is also helpful for rebasing (since the same script can just be re-run on the new master commit).

To create a scripted-diff:

  • start the commit message with scripted-diff: (and then a description of the diff on the same line)
  • in the commit message include the bash script between lines containing just the following text:
    • -BEGIN VERIFY SCRIPT-
    • -END VERIFY SCRIPT-

The scripted-diff is verified by the tool test/lint/commit-script-check.sh. The tool's default behavior, when supplied with a commit is to verify all scripted-diffs from the beginning of time up to said commit. Internally, the tool passes the first supplied argument to git rev-list --reverse to determine which commits to verify script-diffs for, ignoring commits that don't conform to the commit message format described above.

For development, it might be more convenient to verify all scripted-diffs in a range A..B, for example:

test/lint/commit-script-check.sh origin/master..HEAD

Suggestions and examples

If you need to replace in multiple files, prefer git ls-files to find or globbing, and git grep to grep, to avoid changing files that are not under version control.

For efficient replacement scripts, reduce the selection to the files that potentially need to be modified, so for example, instead of a blanket git ls-files src | xargs sed -i s/apple/orange/, use git grep -l apple src | xargs sed -i s/apple/orange/.

Also, it is good to keep the selection of files as specific as possible — for example, replace only in directories where you expect replacements — because it reduces the risk that a rebase of your commit by re-running the script will introduce accidental changes.

Some good examples of scripted-diff:

To find all previous uses of scripted diffs in the repository, do:

git log --grep="-BEGIN VERIFY SCRIPT-"

Release notes

Release notes should be written for any PR that:

  • introduces a notable new feature
  • fixes a significant bug
  • changes an API or configuration model
  • makes any other visible change to the end-user experience.

Release notes should be added to a PR-specific release note file at /doc/release-notes-<PR number>.md to avoid conflicts between multiple PRs. All release-notes* files are merged into a single /doc/release-notes.md file prior to the release.

RPC interface guidelines

A few guidelines for introducing and reviewing new RPC interfaces:

  • Method naming: use consecutive lower-case names such as getrawtransaction and submitblock.

    • Rationale: Consistency with the existing interface.

  • Argument naming: use snake case fee_delta (and not, e.g. camel case feeDelta)

    • Rationale: Consistency with the existing interface.

  • Use the JSON parser for parsing, don't manually parse integers or strings from arguments unless absolutely necessary.

    • Rationale: Introduces hand-rolled string manipulation code at both the caller and callee sites, which is error-prone, and it is easy to get things such as escaping wrong. JSON already supports nested data structures, no need to re-invent the wheel.

    • Exception: AmountFromValue can parse amounts as string. This was introduced because many JSON parsers and formatters hard-code handling decimal numbers as floating-point values, resulting in potential loss of precision. This is unacceptable for monetary values. Always use AmountFromValue and ValueFromAmount when inputting or outputting monetary values. The only exceptions to this are prioritisetransaction and getblocktemplate because their interface is specified as-is in BIP22.

  • Missing arguments and 'null' should be treated the same: as default values. If there is no default value, both cases should fail in the same way. The easiest way to follow this guideline is to detect unspecified arguments with params[x].isNull() instead of params.size() <= x. The former returns true if the argument is either null or missing, while the latter returns true if it is missing, and false if it is null.

    • Rationale: Avoids surprises when switching to name-based arguments. Missing name-based arguments are passed as 'null'.

  • Try not to overload methods on argument type. E.g. don't make getblock(true) and getblock("hash") do different things.

    • Rationale: This is impossible to use with gridcoinresearchd, and can be surprising to users.

    • Exception: Some RPC calls can take both an int and bool, most notably when a bool was switched to a multi-value, or due to other historical reasons. Always have false map to 0 and true to 1 in this case.

  • Don't forget to fill in the argument names correctly in the RPC command table.

    • Rationale: If not, the call can not be used with name-based arguments.

  • Add every non-string RPC argument (method, idx, name) to the table vRPCConvertParams in rpc/client.cpp.

    • Rationale: gridcoinresearchd and the GUI debug console use this table to determine how to convert a plaintext command line to JSON. If the types don't match, the method can be unusable from there.

  • An RPC method must either be a wallet method or a non-wallet method. Do not introduce new methods that differ in behavior based on the presence of a wallet.

    • Rationale: As well as complicating the implementation and interfering with the introduction of multi-wallet, wallet and non-wallet code should be separated to avoid introducing circular dependencies between code units.

  • Try to make the RPC response a JSON object.

    • Rationale: If an RPC response is not a JSON object, then it is harder to avoid API breakage if new data in the response is needed.

  • Be aware of RPC method aliases and generally avoid registering the same callback function pointer for different RPCs.

    • Rationale: RPC methods registered with the same function pointer will be considered aliases and only the first method name will show up in the help RPC command list.

    • Exception: Using RPC method aliases may be appropriate in cases where a new RPC is replacing a deprecated RPC, to avoid both RPCs confusingly showing up in the command list.

  • Use clearly invalid Base58Check addresses for RPCExamples help documentation.

    • Rationale: Prevent accidental transactions by users.

  • Use the UNIX_EPOCH_TIME constant when describing UNIX epoch time or timestamps in the documentation.

    • Rationale: User-facing consistency.