Revealing the Man Behind the Curtain

1
Revealing the Man Behind the Curtain

• Designing a Runtime Library for D

2
The Language

• High-level programming
• Dynamic and associative arrays
• Garbage collection
• Unicode-aware
• Systems programming
• Pointers
• Inline assembly
• Direct calling of C code

3
User Requirements

• High-level
• Low barrier for entry / ease of use
• It should be trivial to write a simple
  application
• Applications should behave in a safe and
  predictable manner by default
• Systems-oriented
• Specialized information or access
• Systems applications can often benefit from
  access to low-level information about the program
  or control over program behavior
• Only get what you pay for
• Systems programmers may have very explicit
  requirements regarding code size, so hidden
  dependencies must be avoided

4
Designer RequirementsThe Compiler Writer

• Language support routines
• Dynamic array manipulation
• Concatenation
• Resizing
• Sorting
• Associative arrays
• UTF conversions
• Memory allocation / garbage collection

5
Designer RequirementsThe Library Developer

• User-accessible code
• Thread management
• Error handling
• Input/output
• Text processing

6
First Cut Monolithic

• Resources
• Compiler team and library team
• Team Interaction
• Close collaboration for integrated features
• Multithreading
• Language / system exceptions
• User control of garbage collection
• Synchronized / inclusive releases

7
Second Cut A Binary Design

• Must formalize the interaction between components
  to decouple development effort
• Language support component
• Standard library component
• Design limitations to eliminate compile-time
  dependencies
• Functions
• Structs
• Simple data types

8
Standard Library Interface Threads

• The garbage collector must interact with thread
  code to coordinate collection
• void thread_suspendAll()
• void thread_scanAll( void delegate( void, void
  ) scan,
• void curStackTop null )
• void thread_resumeAll()

9
Standard Library Interface Exceptions

• Expose a means of signaling system errors to
  decouple exception hierarchy from language
  support component
• void onArrayBoundsError( char file, size_t line
  )
• void onAssertError( char file, uint line )
• void onOutOfMemoryError()

10
Third Cut A Modular Design

• Garbage collector research
• Team skills memory allocator and garbage
  collector design is a specialized field
• Utilize externally developed garbage collectors
  to minimize team effort and obtain best of
  breed implementation
• Varying needs of the users
• Specialized garbage collectors
• Typical vs. real-time

11
Language Support Interface Platform-Specific
Functionality

• The compiler is most suited for providing
  information about the target architecture
• void rt_stackTop()
• void rt_stackBottom()
• void rt_scanStaticData( void delegate( void,
  void ) )
• void rt_finalize( void p, bool det true )

12
Memory Management Interface

• void gc_enable()
• void gc_disable()
• void gc_collect()
• uint gc_getAttr( void p )
• uint gc_setAttr( void p, uint a )
• uint gc_clrAttr( void p, uint a )
• void gc_malloc( size_t sz, uint ba 0 )
• void gc_calloc( size_t sz, uint ba 0 )
• void gc_realloc( void p, size_t sz, uint ba
  0 )
• void gc_free( void p )
• size_t gc_sizeOf( void p )

13
The Design Realized

• Three components
• Language support
• Garbage collector
• Standard library
• Proof of concept Replaceable GC
• Mark / sweep vs. C malloc
• Link-time selection

14

• private import tango.stdc.stdlib
• private extern (C) void thread_init()
• private extern (C) void onOutOfMemoryError()
• extern (C) void gc_malloc( size_t sz, uint ba
  0 )
• void p malloc( sz )
• if( sz p is null ) onOutOfMemoryError()
• return p
• extern (C) void gc_calloc( size_t sz, uint ba
  0 )
• void p calloc( 1, sz )
• if( sz p is null ) onOutOfMemoryError()
• return p
• extern (C) void gc_realloc( void p, size_t sz,
  uint ba 0 )

15

• import tango.core.Memory
• import tango.stdc.stdio
• class C
• this( char n )
• printf( "ctor .s\n", name n )
• this()
• printf( "dtor .s\n", name )
• char name
• void main()
• auto autoVal new C( "autoVal" )

16

• 31,744 gcbasic.lib
• 1,517 gcmalloc.d
• 383 Main.d
• 199,680 phobos.lib
• 66,048 tango.lib
• gt dmd -release Main gcbasic.lib tango.lib
• gt Main
• ctor autoVal
• ctor scopeVal
• dtor autoVal
• dtor scopeVal
• gt dmd -release Main gcmalloc.d tango.lib
• gt Main
• ctor autoVal
• ctor scopeVal
• dtor scopeVal

17
Leak Detection and Disposable

• Validate program behavior
• Specialized clean-up
• void rt_finalize( void p, bool det true )
• bool onCollectResource( Object obj )

18

• class Disposable
• this() printf( "dtor Disposable\n"
  )
• void dispose() printf( "dispose
  Disposable\n" )
• static this() GC.collectHandler onCollect
• bool onCollect( Object o )
• if( auto d cast(Disposable) o )
• d.dispose() return false
• return true
• void discardDisposable()
• auto d new Disposable
• void main()

gt Main delete dtor Disposable
GC.collect dispose Disposable
19
Overridable Object Monitors

• Given the following interface
• class Object
• interface Monitor
• void lock()
• void unlock()
• Object monitors must be strucutred as
• alias Object.Monitor IMonitor
• struct Monitor
• IMonitor impl
• / data /

20
Library Mutexes as Object Monitors

• auto mutex new Mutex
• auto cond new Condition
• bool ready false
• synchronized( mutex )
• while( !ready )
• cond.wait() // mutex released / acquired
• synchronized( mutex )
• ready true
• cond.notify()