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Create developer-notes.md
Moves coding guidelines and development tips/tricks into a single file. Also adds a section explaining pull request terminology.
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Michael Ford
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doc/developer-notes.md
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Coding
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====================
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Various coding styles have been used during the history of the codebase,
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and the result is not very consistent. However, we're now trying to converge to
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a single style, so please use it in new code. Old code will be converted
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gradually.
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- Basic rules specified in src/.clang-format. Use a recent clang-format-3.5 to format automatically.
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- Braces on new lines for namespaces, classes, functions, methods.
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- Braces on the same line for everything else.
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- 4 space indentation (no tabs) for every block except namespaces.
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- No indentation for public/protected/private or for namespaces.
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- No extra spaces inside parenthesis; don't do ( this )
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- No space after function names; one space after if, for and while.
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Block style example:
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```c++
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namespace foo
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{
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class Class
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{
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bool Function(char* psz, int n)
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{
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// Comment summarising what this section of code does
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for (int i = 0; i < n; i++) {
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// When something fails, return early
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if (!Something())
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return false;
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...
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}
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// Success return is usually at the end
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return true;
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}
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}
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}
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```
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Doxygen comments
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-----------------
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To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields.
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For example, to describe a function use:
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```c++
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/**
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* ... text ...
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* @param[in] arg1 A description
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* @param[in] arg2 Another argument description
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* @pre Precondition for function...
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*/
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bool function(int arg1, const char *arg2)
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```
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A complete list of `@xxx` commands can be found at http://www.stack.nl/~dimitri/doxygen/manual/commands.html.
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As Doxygen recognizes the comments by the delimiters (`/**` and `*/` in this case), you don't
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*need* to provide any commands for a comment to be valid, just a description text is fine.
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To describe a class use the same construct above the class definition:
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```c++
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/**
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* Alerts are for notifying old versions if they become too obsolete and
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* need to upgrade. The message is displayed in the status bar.
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* @see GetWarnings()
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*/
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class CAlert
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{
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```
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To describe a member or variable use:
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```c++
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int var; //!< Detailed description after the member
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```
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Also OK:
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```c++
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///
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/// ... text ...
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///
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bool function2(int arg1, const char *arg2)
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```
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Not OK (used plenty in the current source, but not picked up):
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```c++
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//
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// ... text ...
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//
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```
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A full list of comment syntaxes picked up by doxygen can be found at http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html,
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but if possible use one of the above styles.
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Development tips and tricks
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---------------------------
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**compiling for debugging**
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Run configure with the --enable-debug option, then make. Or run configure with
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CXXFLAGS="-g -ggdb -O0" or whatever debug flags you need.
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**debug.log**
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If the code is behaving strangely, take a look in the debug.log file in the data directory;
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error and debugging messages are written there.
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The -debug=... command-line option controls debugging; running with just -debug will turn
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on all categories (and give you a very large debug.log file).
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The Qt code routes qDebug() output to debug.log under category "qt": run with -debug=qt
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to see it.
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**testnet and regtest modes**
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Run with the -testnet option to run with "play bitcoins" on the test network, if you
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are testing multi-machine code that needs to operate across the internet.
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If you are testing something that can run on one machine, run with the -regtest option.
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In regression test mode, blocks can be created on-demand; see qa/rpc-tests/ for tests
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that run in -regtest mode.
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**DEBUG_LOCKORDER**
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Bitcoin Core is a multithreaded application, and deadlocks or other multithreading bugs
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can be very difficult to track down. Compiling with -DDEBUG_LOCKORDER (configure
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CXXFLAGS="-DDEBUG_LOCKORDER -g") inserts run-time checks to keep track of which locks
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are held, and adds warnings to the debug.log file if inconsistencies are detected.
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Locking/mutex usage notes
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-------------------------
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The code is multi-threaded, and uses mutexes and the
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LOCK/TRY_LOCK macros to protect data structures.
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Deadlocks due to inconsistent lock ordering (thread 1 locks cs_main
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and then cs_wallet, while thread 2 locks them in the opposite order:
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result, deadlock as each waits for the other to release its lock) are
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a problem. Compile with -DDEBUG_LOCKORDER to get lock order
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inconsistencies reported in the debug.log file.
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Re-architecting the core code so there are better-defined interfaces
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between the various components is a goal, with any necessary locking
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done by the components (e.g. see the self-contained CKeyStore class
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and its cs_KeyStore lock for example).
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Threads
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-------
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- ThreadScriptCheck : Verifies block scripts.
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- ThreadImport : Loads blocks from blk*.dat files or bootstrap.dat.
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- StartNode : Starts other threads.
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- ThreadDNSAddressSeed : Loads addresses of peers from the DNS.
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- ThreadMapPort : Universal plug-and-play startup/shutdown
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- ThreadSocketHandler : Sends/Receives data from peers on port 8333.
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- ThreadOpenAddedConnections : Opens network connections to added nodes.
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- ThreadOpenConnections : Initiates new connections to peers.
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- ThreadMessageHandler : Higher-level message handling (sending and receiving).
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- DumpAddresses : Dumps IP addresses of nodes to peers.dat.
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- ThreadFlushWalletDB : Close the wallet.dat file if it hasn't been used in 500ms.
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- ThreadRPCServer : Remote procedure call handler, listens on port 8332 for connections and services them.
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- BitcoinMiner : Generates bitcoins (if wallet is enabled).
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- Shutdown : Does an orderly shutdown of everything.
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Pull Request Terminology
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------------------------
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Concept ACK - Agree with the idea and overall direction, but haven't reviewed the code changes or tested them.
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utACK (untested ACK) - Reviewed and agree with the code changes but haven't actually tested them.
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Tested ACK - Reviewed the code changes and have verified the functionality or bug fix.
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ACK - A loose ACK can be confusing. It's best to avoid them unless it's a documentation/comment only change in which case there is nothing to test/verify; therefore the tested/untested distinction is not there.
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NACK - Disagree with the code changes/concept. Should be accompanied by an explanation.
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