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- [/
- Copyright Oliver Kowalke 2014.
- 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]
- 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(size)`]
- []
- [creates a stack allocator]
- ]
- [
- [`a.allocate()`]
- [`stack_context`]
- [creates a stack]
- ]
- [
- [`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
- __econtext__.]
- [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).]
- [section:protected_fixedsize Class ['protected_fixedsize]]
- __boost_coroutine__ provides the class __protected_fixedsize__ 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_fixedsize__ 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/coroutine2/protected_fixedsize.hpp>
- struct protected_fixedsize {
- protected_fixesize(std::size_t size = traits_type::default_size());
- stack_context allocate();
- void deallocate( stack_context &);
- }
- [heading `stack_context allocate()`]
- [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:pooled_fixedsize Class ['pooled_fixedsize_stack]]
- __boost_coroutine__ provides the class __pooled_fixedsize__ which models
- the __stack_allocator_concept__.
- In contrast to __protected_fixedsize__ it does not append a guard page at the
- end of each stack. The memory is managed internally by
- [@http://www.boost.org/doc/libs/release/libs/pool/doc/html/boost/pool.html `boost::pool<>`].
- #include <boost/coroutine2/pooled_fixedsize_stack.hpp>
- struct pooled_fixedsize_stack {
- pooled_fixedsize_stack(std::size_t size = traits_type::default_size());
- stack_context allocate();
- void deallocate( stack_context &);
- }
- [heading `pooled_fixedsize_stack(std::size_t stack_size, std::size_t next_size, std::size_t max_size)`]
- [variablelist
- [[Preconditions:] [`! traits_type::is_unbounded() && ( traits_type::maximum:size() >= stack_size)`
- and `0 < nest_size`.]]
- [[Effects:] [Allocates memory of at least `stack_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. Argument `next_size` determines the number of stacks to
- request from the system the first time that `*this` needs to allocate system
- memory. The third argument `max_size` controls how many memory might be
- allocated for stacks - a value of zero means no uper limit.]]
- ]
- [heading `stack_context allocate()`]
- [variablelist
- [[Preconditions:] [`! 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::is_unbounded() && ( traits_type::maximum:size() >= sctx.size)`.]]
- [[Effects:] [Deallocates the stack space.]]
- ]
- [endsect]
- [section:fixedsize Class ['fixedsize_stack]]
- __boost_coroutine__ provides the class __fixedsize__ which models
- the __stack_allocator_concept__.
- In contrast to __protected_fixedsize__ it does not append a guard page at the
- end of each stack. The memory is simply managed by `std::malloc()` and
- `std::free()`.
- #include <boost/context/fixedsize_stack.hpp>
- struct fixedsize_stack {
- fixedsize_stack(std::size_t size = traits_type::default_size());
- stack_context allocate();
- void deallocate( stack_context &);
- }
- [heading `stack_context allocate()`]
- [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]
- [#segmented]
- [section:segmented Class ['segmented_stack]]
- __boost_coroutine__ supports usage of a __segmented__, 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__ models the __stack_allocator_concept__.
- In contrast to __protected_fixedsize__ and __fixedsize__ it creates a
- stack which grows on demand.
- [note Segmented stacks are currently only supported by [*gcc] from version
- [*4.7] [*clang] from version [*3.4] onwards. In order to use a
- __segmented_stack__ __boost_context__ must be built with
- property `segmented-stacks`, e.g. [*toolset=gcc segmented-stacks=on] and
- applying `BOOST_USE_SEGMENTED_STACKS` and `BOOST_USE_UCONTEXT` at b2/bjam
- command line.]
- #include <boost/coroutine2/segmented_stack.hpp>
- struct segmented_stack {
- segmented_stack(std::size_t size = traits_type::default_size());
- stack_context allocate();
- void deallocate( stack_context &);
- }
- [heading `stack_context allocate()`]
- [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.]]
- ]
- [note If the library is compiled for segmented stacks, __segmented_stack__ is the only
- available stack allocator.]
- [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.
- 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_context__ contains some extra control
- structures.
- struct stack_context
- {
- void * sp;
- std::size_t size;
- // might contain additional control structures
- // 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]
- [section:sanitizers Support for sanitizers]
- Sanitizers (GCC/Clang) are confused by the stack switches.
- The library (and Boost.Context too) is required to be compiled with property (b2 command-line)
- `context-impl=ucontext` and compilers santizer options.
- Users must define `BOOST_USE_ASAN` before including any Boost.Context headers
- when linking against Boost binaries.
- [endsect]
- [endsect]
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