Developer Notes
===============

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.
- Basic rules specified in src/.clang-format. Use a recent clang-format-3.5 to format automatically.
  - Braces on new lines for namespaces, 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 namespaces.
  - No extra spaces inside parenthesis; don't do ( this )
  - No space after function names; one space after if, for and while.

Block style example:
```c++
namespace foo
{
class Class
{
    bool Function(char* psz, 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;
            ...
        }

        // Success return is usually at the end
        return true;
    }
}
}
```

Doxygen comments
-----------------

To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields.

For example, to describe a function use:
```c++
/**
 * ... 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:
```c++
/**
 * 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:
```c++
int var; //!< Detailed description after the member
```

Also OK:
```c++
///
/// ... text ...
///
bool function2(int arg1, const char *arg2)
```

Not OK (used plenty in the current source, but not picked up):
```c++
//
// ... 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.

Development tips and tricks
---------------------------

**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 bitcoins" 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**

Bitcoin 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.

Locking/mutex usage notes
-------------------------

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).

Threads
-------

- 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 8333.

- 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 8332 for connections and services them.

- BitcoinMiner : Generates bitcoins (if wallet is enabled).

- Shutdown : Does an orderly shutdown of everything.

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 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.

