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# GHC Commentary: The Runtime System
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GHC's runtime system is a slightly scary beast: 50,000 lines of C and C-- code, much of which seems at first glance to be completely obscure. What on earth does the RTS *do*? Here are the highlights:
Original source:
- It includes all the bits required to execute Haskell code that aren't compiled into the code itself.
For example, the RTS contains the code that knows how to raise an exception when you call `error`,
and code to implement the multi-precision `Integer` operations (via the GMP library).
```trac
- It includes a sophisticated storage manager, including a multi-generational garbage collector with copying
= GHC Commentary: The Runtime System =
GHC's runtime system is a slightly scary beast: 50,000 lines of C and C-- code, much of which seems at first glance to be completely obscure. What on earth does the RTS ''do''? Here are the highlights:
* It includes all the bits required to execute Haskell code that aren't compiled into the code itself.
For example, the RTS contains the code that knows how to raise an exception when you call {{{error}}},
and code to implement the multi-precision {{{Integer}}} operations (via the GMP library).
* It includes a sophisticated storage manager, including a multi-generational garbage collector with copying
and compacting strategies.
- It includes a user-space scheduler for Haskell threads, together with support for scheduling Haskell threads
* It includes a user-space scheduler for Haskell threads, together with support for scheduling Haskell threads
across multiple CPUs, and allowing Haskell threads to call foreign functions in separate OS threads.
- There's a byte-code interpreter for GHCi, and a dynamic linker for loading up object code into a GHCi session.
- Heap-profiling (of various kinds) and time-profiling of Haskell code are included.
* There's a byte-code interpreter for GHCi, and a dynamic linker for loading up object code into a GHCi session.
- Support for Software Transactional Memory is now included...
* Heap-profiling (of various kinds) and time-profiling of Haskell code are included.
* Support for Software Transactional Memory is now included...
Next, we try to make sense of how it all fits together.
## Block Diagram
[](/trac/ghc/attachment/wiki/Commentary/Rts/rts-overview.png)
## RTS: Contents
- [RTS Configurations](commentary/rts/config)
- [The Word](commentary/rts/word)
- [What the hell is a .cmm file?](commentary/rts/cmm)
- [Layout of heap objects](commentary/rts/heap-objects)
- [Layout of the stack](commentary/rts/stack)
- Slop?
- [Sanity Checking](commentary/rts/sanity)
- [The Haskell Execution model](commentary/rts/haskell-execution)
- [The Scheduler](commentary/rts/scheduler)
- [The Storage Manager](commentary/rts/storage)
- [So how does foreign import "wrapper" work?](commentary/rts/ffi)
- [GHCi support: the byte-code interpreter and dynamic linker](commentary/rts/interpreter)
- [Asynchronous exceptions](commentary/rts/async-exceptions)
- [Software Transactional Memory (STM)](commentary/rts/stm)
- [Garbage Collecting CAFs](commentary/rts/ca-fs)
- [Weak Pointers and Finalizers](commentary/rts/weak)
- [Coding conventions in the RTS](commentary/rts/conventions)
\ No newline at end of file
== Block Diagram ==
[[Image(rts-overview.png)]]
== RTS: Contents ==
* [wiki:Commentary/Rts/Config RTS Configurations]
* [wiki:Commentary/Rts/Word The Word]
* [wiki:Commentary/Rts/Cmm What the hell is a .cmm file?]
* [wiki:Commentary/Rts/Storage The Storage Manager]
* [wiki:Commentary/Rts/Stack Layout of the stack]
* [wiki:Commentary/Rts/Slop Slop]
* [wiki:Commentary/Rts/Sanity Sanity Checking]
* [wiki:Commentary/Rts/HaskellExecution The Haskell Execution model]
* [wiki:Commentary/Rts/Scheduler The Scheduler]
* [wiki:Commentary/Rts/FFI So how does foreign import "wrapper" work?]
* [wiki:Commentary/Rts/Interpreter GHCi support: the byte-code interpreter and dynamic linker]
* [wiki:Commentary/Rts/AsyncExceptions Asynchronous exceptions]
* [wiki:Commentary/Rts/STM Software Transactional Memory (STM)]
* [wiki:Commentary/Rts/CAFs Garbage Collecting CAFs]
* [wiki:Commentary/Rts/Weak Weak Pointers and Finalizers]
* [wiki:Commentary/Rts/Conventions Coding conventions in the RTS]
```