doc/developer-notes.md
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, so please use it in new code. Old code will be converted gradually and you are encouraged to use the provided clang-format-diff script to clean up the patch automatically before submitting a pull request.
public/protected/private or for namespace.if, for and while.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.++i is preferred over i++.Block style example:
namespace foo
{
class Class
{
bool Function(const std::string& s, int n)
{
// Comment summarising what this section of code does
for (int i = 0; i < n; ++i) {
// When something fails, return early
if (!Something()) return false;
...
if (SomethingElse()) {
DoMore();
} else {
DoLess();
}
}
// Success return is usually at the end
return true;
}
}
}
To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields.
For example, to describe a function use:
/**
* ... text ...
* @param[in] arg1 A description
* @param[in] arg2 Another argument description
* @pre Precondition for function...
*/
bool function(int arg1, const char *arg2)
A complete list of @xxx commands can be found at http://www.stack.nl/~dimitri/doxygen/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:
int var; //!< Detailed description after the member
or
//! Description before the member
int var;
Also OK:
///
/// ... text ...
///
bool function2(int arg1, const char *arg2)
Not OK (used plenty in the current source, but not picked up):
//
// ... text ...
//
A full list of comment syntaxes picked up by doxygen can be found at http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html, but if possible use one of the above styles.
compiling for debugging
Run configure with the --enable-debug option, then make. Or run configure with CXXFLAGS="-g -ggdb -O0" or whatever debug flags you need.
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=... command-line option controls debugging; running with just -debug or -debug=1 will turn on all categories (and give you a very large debug.log file).
The Qt code routes qDebug() output to debug.log under category "qt": run with -debug=qt to see it.
testnet and regtest modes
Run with the -testnet option to run with "play dogecoins" on the test network, if you are testing multi-machine code that needs to operate across the internet.
If you are testing something that can run on one machine, run with the -regtest option. In regression test mode, blocks can be created on-demand; see qa/rpc-tests/ for tests that run in -regtest mode.
DEBUG_LOCKORDER
Dogecoin Core is a multithreaded application, and deadlocks or other multithreading bugs can be very difficult to track down. Compiling with -DDEBUG_LOCKORDER (configure CXXFLAGS="-DDEBUG_LOCKORDER -g") inserts run-time checks to keep track of which locks are held, and adds warnings to the debug.log file if inconsistencies are detected.
The code is multi-threaded, and uses mutexes and the LOCK/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 -DDEBUG_LOCKORDER to get lock order inconsistencies reported in the debug.log file.
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 and its cs_KeyStore lock for example).
ThreadScriptCheck : Verifies block scripts.
ThreadImport : Loads blocks from blk*.dat files or bootstrap.dat.
StartNode : Starts other threads.
ThreadDNSAddressSeed : Loads addresses of peers from the DNS.
ThreadMapPort : Universal plug-and-play startup/shutdown
ThreadSocketHandler : Sends/Receives data from peers on port 22556.
ThreadOpenAddedConnections : Opens network connections to added nodes.
ThreadOpenConnections : Initiates new connections to peers.
ThreadMessageHandler : Higher-level message handling (sending and receiving).
DumpAddresses : Dumps IP addresses of nodes to peers.dat.
ThreadFlushWalletDB : Close the wallet.dat file if it hasn't been used in 500ms.
ThreadRPCServer : Remote procedure call handler, listens on port 22555 for connections and services them.
DogecoinMiner : Generates dogecoins (if wallet is enabled).
Shutdown : Does an orderly shutdown of everything.
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 Bitcoin 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 the repository (for
example, lcov) it is perfectly acceptable to add its files to .gitignore
and commit them.
A few non-style-related recommendations for developers, as well as points to pay attention to for reviewers of Bitcoin Core code.
New features should be exposed on RPC first, then can be made available in the GUI
Make sure pull requests pass Travis 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
Make sure that no crashes happen with run-time option -disablewallet.
validateaddress) it is easy to forget that global pointer pwalletMain
can be NULL. See qa/rpc-tests/disablewallet.py for functional tests
exercising the API with -disablewalletInclude db_cxx.h (BerkeleyDB header) only when ENABLE_WALLET is set
Assertions should not have side-effects
If you use the .h, you must link the .cpp
.h to the .cpp should not result in build errorsUse the RAII (Resource Acquisition Is Initialization) paradigm where possible. For example by using
unique_ptr for allocations in a function.
Never use the std::map [] syntax when reading from a map, but instead use .find()
[] 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 mapDo not compare an iterator from one data structure with an iterator of another data structure (even if of the same type)
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
Make sure that constructors initialize all fields. If this is skipped for a good reason (i.e., optimization on the critical path), add an explicit comment about this
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
Be careful of LogPrint versus LogPrintf. LogPrint takes a category argument, LogPrintf does not.
Use std::string, avoid C string manipulation functions
\0 characters. Also some C string manipulations
tend to act differently depending on platform, or even the user localeUse ParseInt32, ParseInt64, ParseUInt32, ParseUInt64, ParseDouble from utilstrencodings.h for number parsing
For strprintf, LogPrint, LogPrintf formatting characters don't need size specifiers
The shadowing warning (-Wshadow) is enabled by default. It prevents issues rising
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.
E.g. in member initializers, prepend _ to the argument name shadowing the
member name:
class AddressBookPage
{
Mode mode;
}
AddressBookPage::AddressBookPage(Mode _mode) :
mode(_mode)
...
When using nested cycles, do not name the inner cycle variable the same as in upper cycle etc.
Build and run tests with -DDEBUG_LOCKORDER to verify that no potential
deadlocks are introduced. As of 0.12, this is defined by default when
configuring with --enable-debug
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);
{
...
}
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
Don't import anything into the global namespace (using namespace ...). Use
fully specified types such as std::string.
Do not display or manipulate dialogs in model code (classes *Model)
Several parts of the repository are subtrees of software maintained elsewhere.
Some of these are maintained by active developers of Bitcoin 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 Bitcoin Core so that they can be integrated quickly. Cosmetic changes should be purely taken upstream.
There is a tool in contrib/devtools/git-subtree-check.sh to check a subtree directory for consistency with its upstream repository.
Current subtrees include:
src/leveldb
src/libsecp256k1
src/crypto/ctaes
src/univalue
For resolving merge/rebase conflicts, it can be useful to enable diff3 style using
git config merge.conflictstyle diff3. Instead of
<<<
yours
===
theirs
>>>
you will see
<<<
yours
|||
original
===
theirs
>>>
This may make it much clearer what caused the conflict. In this style, you can often just look at what changed between original and theirs, and mechanically apply that to yours (or the other way around).
When reviewing patches which change indentation in C++ files, use git diff -w and git show -w. This makes
the diff algorithm ignore whitespace changes. This feature is also available on github.com, by adding ?w=1
at the end of any URL which shows a diff.
When reviewing patches that change symbol names in many places, use git diff --word-diff. This will instead
of showing the patch as deleted/added lines, show deleted/added words.
When reviewing patches that move code around, try using
git diff --patience commit~:old/file.cpp commit:new/file/name.cpp, and ignoring everything except the
moved body of code which should show up as neither + or - lines. In case it was not a pure move, this may
even work when combined with the -w or --word-diff options described above.
When looking at other's pull requests, it may make sense to add the following section to your .git/config
file:
[remote "upstream-pull"]
fetch = +refs/pull/*:refs/remotes/upstream-pull/*
url = [email protected]:dogecoin/dogecoin.git
This will add an upstream-pull remote to your git repository, which can be fetched using git fetch --all
or git fetch upstream-pull. Afterwards, you can use upstream-pull/NUMBER/head in arguments to git show,
git checkout and anywhere a commit id would be acceptable to see the changes from pull request NUMBER.