296 lines
9.4 KiB
Plaintext
296 lines
9.4 KiB
Plaintext
[/
|
|
Copyright Oliver Kowalke 2009.
|
|
Distributed under the Boost Software License, Version 1.0.
|
|
(See accompanying file LICENSE_1_0.txt or copy at
|
|
http://www.boost.org/LICENSE_1_0.txt
|
|
]
|
|
|
|
[section:stack Stack allocation]
|
|
|
|
A __coro__ uses internally a __ctx__ which manages a set of registers and a stack.
|
|
The memory used by the stack is allocated/deallocated via a __stack_allocator__
|
|
which is required to model a __stack_allocator_concept__.
|
|
|
|
|
|
[heading __stack_allocator_concept__]
|
|
A __stack_allocator__ must satisfy the __stack_allocator_concept__ requirements
|
|
shown in the following table, in which `a` is an object of a
|
|
__stack_allocator__ type, `sctx` is a `stack_context`, and `size` is a `std::size_t`:
|
|
|
|
[table
|
|
[[expression][return type][notes]]
|
|
[
|
|
[`a.allocate( sctx, size)`]
|
|
[`void`]
|
|
[creates a stack of at least `size` bytes and stores its pointer and
|
|
length in `sctx`]
|
|
]
|
|
[
|
|
[`a.deallocate( sctx)`]
|
|
[`void`]
|
|
[deallocates the stack created by `a.allocate()`]
|
|
]
|
|
]
|
|
|
|
[important The implementation of `allocate()` might include logic to protect
|
|
against exceeding the context's available stack size rather than leaving it as
|
|
undefined behaviour.]
|
|
|
|
[important Calling `deallocate()` with a `stack_context` not set by `allocate()`
|
|
results in undefined behaviour.]
|
|
|
|
[note The stack is not required to be aligned; alignment takes place inside
|
|
__coro__.]
|
|
|
|
[note Depending on the architecture `allocate()` stores an address from the
|
|
top of the stack (growing downwards) or the bottom of the stack (growing
|
|
upwards).]
|
|
|
|
class __coro_allocator__ is a typedef of __standard_allocator__.
|
|
|
|
|
|
[section:protected_stack_allocator Class ['protected_stack_allocator]]
|
|
|
|
__boost_coroutine__ provides the class __protected_allocator__ which models
|
|
the __stack_allocator_concept__.
|
|
It appends a guard page at the end of each stack to protect against exceeding
|
|
the stack. If the guard page is accessed (read or write operation) a
|
|
segmentation fault/access violation is generated by the operating system.
|
|
|
|
[important Using __protected_allocator__ is expensive. That is, launching a
|
|
new coroutine with a new stack is expensive; the allocated stack is just as
|
|
efficient to use as any other stack.]
|
|
|
|
[note The appended `guard page` is [*not] mapped to physical memory, only
|
|
virtual addresses are used.]
|
|
|
|
#include <boost/coroutine/protected_stack_allocator.hpp>
|
|
|
|
template< typename traitsT >
|
|
struct basic_protected_stack_allocator
|
|
{
|
|
typedef traitT traits_type;
|
|
|
|
void allocate( stack_context &, std::size_t size);
|
|
|
|
void deallocate( stack_context &);
|
|
}
|
|
|
|
typedef basic_protected_stack_allocator< stack_traits > protected_stack_allocator
|
|
|
|
[heading `void allocate( stack_context & sctx, std::size_t size)`]
|
|
[variablelist
|
|
[[Preconditions:] [`traits_type::minimum_size() <= size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= size)`.]]
|
|
[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer
|
|
to the stack and its actual size in `sctx`. Depending
|
|
on the architecture (the stack grows downwards/upwards) the stored address is
|
|
the highest/lowest address of the stack.]]
|
|
]
|
|
|
|
[heading `void deallocate( stack_context & sctx)`]
|
|
[variablelist
|
|
[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= sctx.size)`.]]
|
|
[[Effects:] [Deallocates the stack space.]]
|
|
]
|
|
|
|
[endsect]
|
|
|
|
|
|
[section:standard_stack_allocator Class ['standard_stack_allocator]]
|
|
|
|
__boost_coroutine__ provides the class __standard_allocator__ which models
|
|
the __stack_allocator_concept__.
|
|
In contrast to __protected_allocator__ it does not append a guard page at the
|
|
end of each stack. The memory is simply managed by `std::malloc()` and
|
|
`std::free()`.
|
|
|
|
[note The __standard_allocator__ is the default stack allocator.]
|
|
|
|
#include <boost/coroutine/standard_stack_allocator.hpp>
|
|
|
|
template< typename traitsT >
|
|
struct standard_stack_allocator
|
|
{
|
|
typedef traitT traits_type;
|
|
|
|
void allocate( stack_context &, std::size_t size);
|
|
|
|
void deallocate( stack_context &);
|
|
}
|
|
|
|
typedef basic_standard_stack_allocator< stack_traits > standard_stack_allocator
|
|
|
|
[heading `void allocate( stack_context & sctx, std::size_t size)`]
|
|
[variablelist
|
|
[[Preconditions:] [`traits_type::minimum_size() <= size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= size)`.]]
|
|
[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer to
|
|
the stack and its actual size in `sctx`. Depending on the architecture (the
|
|
stack grows downwards/upwards) the stored address is the highest/lowest
|
|
address of the stack.]]
|
|
]
|
|
|
|
[heading `void deallocate( stack_context & sctx)`]
|
|
[variablelist
|
|
[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= sctx.size)`.]]
|
|
[[Effects:] [Deallocates the stack space.]]
|
|
]
|
|
|
|
[endsect]
|
|
|
|
|
|
[section:segmented_stack_allocator Class ['segmented_stack_allocator]]
|
|
|
|
__boost_coroutine__ supports usage of a __segmented_stack__, e. g. the size of
|
|
the stack grows on demand. The coroutine is created with a minimal stack size
|
|
and will be increased as required.
|
|
Class __segmented_allocator__ models the __stack_allocator_concept__.
|
|
In contrast to __protected_allocator__ and __standard_allocator__ it creates a
|
|
stack which grows on demand.
|
|
|
|
[note Segmented stacks are currently only supported by [*gcc] from version
|
|
[*4.7] and [*clang] from version [*3.4] onwards. In order to use a
|
|
__segmented_stack__ __boost_coroutine__ must be built with
|
|
[*toolset=gcc segmented-stacks=on] at b2/bjam command-line. Applications
|
|
must be compiled with compiler-flags
|
|
[*-fsplit-stack -DBOOST_USE_SEGMENTED_STACKS].]
|
|
|
|
#include <boost/coroutine/segmented_stack_allocator.hpp>
|
|
|
|
template< typename traitsT >
|
|
struct basic_segmented_stack_allocator
|
|
{
|
|
typedef traitT traits_type;
|
|
|
|
void allocate( stack_context &, std::size_t size);
|
|
|
|
void deallocate( stack_context &);
|
|
}
|
|
|
|
typedef basic_segmented_stack_allocator< stack_traits > segmented_stack_allocator;
|
|
|
|
[heading `void allocate( stack_context & sctx, std::size_t size)`]
|
|
[variablelist
|
|
[[Preconditions:] [`traits_type::minimum_size() <= size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= size)`.]]
|
|
[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer to
|
|
the stack and its actual size in `sctx`. Depending on the architecture (the
|
|
stack grows downwards/upwards) the stored address is the highest/lowest
|
|
address of the stack.]]
|
|
]
|
|
|
|
[heading `void deallocate( stack_context & sctx)`]
|
|
[variablelist
|
|
[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
|
|
`! traits_type::is_unbounded() && ( traits_type::maximum_size() >= sctx.size)`.]]
|
|
[[Effects:] [Deallocates the stack space.]]
|
|
]
|
|
|
|
[endsect]
|
|
|
|
|
|
[section:stack_traits Class ['stack_traits]]
|
|
|
|
['stack_traits] models a __stack_traits__ providing a way to access certain
|
|
properites defined by the enironment. Stack allocators use __stack_traits__ to
|
|
allocate stacks.
|
|
|
|
#include <boost/coroutine/stack_traits.hpp>
|
|
|
|
struct stack_traits
|
|
{
|
|
static bool is_unbounded() noexcept;
|
|
|
|
static std::size_t page_size() noexcept;
|
|
|
|
static std::size_t default_size() noexcept;
|
|
|
|
static std::size_t minimum_size() noexcept;
|
|
|
|
static std::size_t maximum_size() noexcept;
|
|
}
|
|
|
|
|
|
[heading `static bool is_unbounded()`]
|
|
[variablelist
|
|
[[Returns:] [Returns `true` if the environment defines no limit for the size of
|
|
a stack.]]
|
|
[[Throws:] [Nothing.]]
|
|
]
|
|
|
|
[heading `static std::size_t page_size()`]
|
|
[variablelist
|
|
[[Returns:] [Returns the page size in bytes.]]
|
|
[[Throws:] [Nothing.]]
|
|
]
|
|
|
|
[heading `static std::size_t default_size()`]
|
|
[variablelist
|
|
[[Returns:] [Returns a default stack size, which may be platform specific.
|
|
If the stack is unbounded then the present implementation returns the maximum of
|
|
`64 kB` and `minimum_size()`.]]
|
|
[[Throws:] [Nothing.]]
|
|
]
|
|
|
|
[heading `static std::size_t minimum_size()`]
|
|
[variablelist
|
|
[[Returns:] [Returns the minimum size in bytes of stack defined by the
|
|
environment (Win32 4kB/Win64 8kB, defined by rlimit on POSIX).]]
|
|
[[Throws:] [Nothing.]]
|
|
]
|
|
|
|
[heading `static std::size_t maximum_size()`]
|
|
[variablelist
|
|
[[Preconditions:] [`is_unbounded()` returns `false`.]]
|
|
[[Returns:] [Returns the maximum size in bytes of stack defined by the
|
|
environment.]]
|
|
[[Throws:] [Nothing.]]
|
|
]
|
|
|
|
|
|
[endsect]
|
|
|
|
|
|
[section:stack_context Class ['stack_context]]
|
|
|
|
__boost_coroutine__ provides the class __stack_context__ which will contain
|
|
the stack pointer and the size of the stack.
|
|
In case of a __segmented_stack__, __stack_context__ contains some extra control
|
|
structures.
|
|
|
|
struct stack_context
|
|
{
|
|
void * sp;
|
|
std::size_t size;
|
|
|
|
// might contain additional control structures
|
|
// for instance for segmented stacks
|
|
}
|
|
|
|
[heading `void * sp`]
|
|
[variablelist
|
|
[[Value:] [Pointer to the beginning of the stack.]]
|
|
]
|
|
|
|
[heading `std::size_t size`]
|
|
[variablelist
|
|
[[Value:] [Actual size of the stack.]]
|
|
]
|
|
|
|
[endsect]
|
|
|
|
|
|
[section:valgrind Support for valgrind]
|
|
|
|
Running programs that switch stacks under valgrind causes problems.
|
|
Property (b2 command-line) `valgrind=on` let valgrind treat the memory regions
|
|
as stack space which suppresses the errors.
|
|
|
|
[endsect]
|
|
|
|
|
|
[endsect]
|