304 lines
10 KiB
Plaintext
304 lines
10 KiB
Plaintext
[/
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Copyright Oliver Kowalke 2009-2013.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt
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]
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[#stack]
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[section:stack Stack allocation]
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A __fiber__ uses internally an __econtext__ which manages a set of registers and a stack.
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The memory used by the stack is allocated/deallocated via a __stack_allocator__
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which is required to model a __stack_allocator_concept__.
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A __stack_allocator__ can be passed to [link fiber_fiber `fiber::fiber()`] or
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to [ns_function_link fibers..async].
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[#stack_allocator_concept]
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[heading stack-allocator concept]
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A __stack_allocator__ must satisfy the ['stack-allocator concept] requirements
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shown in the following table, in which `a` is an object of a
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__stack_allocator__ type, `sctx` is a __stack_context__, and `size` is a `std::size_t`:
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[table
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[[expression][return type][notes]]
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[
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[`a(size)`]
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[]
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[creates a stack allocator]
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]
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[
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[`a.allocate()`]
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[__stack_context__]
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[creates a stack]
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]
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[
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[`a.deallocate( sctx)`]
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[`void`]
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[deallocates the stack created by `a.allocate()`]
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]
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]
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[important The implementation of `allocate()` might include logic to protect
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against exceeding the context's available stack size rather than leaving it as
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undefined behaviour.]
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[important Calling `deallocate()` with a __stack_context__ not obtained from
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`allocate()` results in undefined behaviour.]
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[note The memory for the stack is not required to be aligned; alignment takes
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place inside __econtext__.]
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See also [@http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack.html Boost.Context stack allocation].
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In particular, `traits_type` methods are as described for
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[@http://www.boost.org/doc/libs/release/libs/context/doc/html/context/stack/stack_traits.html
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`boost::context::stack_traits`].
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[class_heading protected_fixedsize_stack]
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__boost_fiber__ provides the class __pfixedsize_stack__ which models
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the __stack_allocator_concept__.
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It appends a guard page at the end of each stack to protect against exceeding
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the stack. If the guard page is accessed (read or write operation) a
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segmentation fault/access violation is generated by the operating system.
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[important Using __pfixedsize_stack__ is expensive. Launching a new fiber with
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a stack of this type incurs the overhead of setting the memory protection;
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once allocated, this stack is just as efficient to use as __fixedsize_stack__.]
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[note The appended `guard page` is [*not] mapped to physical memory, only
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virtual addresses are used.]
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#include <boost/fiber/protected_fixedsize.hpp>
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namespace boost {
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namespace fibers {
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struct protected_fixedsize {
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protected_fixesize(std::size_t size = traits_type::default_size());
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stack_context allocate();
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void deallocate( stack_context &);
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}
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}}
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[member_heading protected_fixedsize..allocate]
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stack_context allocate();
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[variablelist
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[[Preconditions:] [`traits_type::minimum_size() <= size` and
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`traits_type::is_unbounded() || ( size <= traits_type::maximum_size() )`.]]
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[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer
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to the stack and its actual size in `sctx`. Depending
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on the architecture (the stack grows downwards/upwards) the stored address is
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the highest/lowest address of the stack.]]
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]
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[member_heading protected_fixesize..deallocate]
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void deallocate( stack_context & sctx);
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[variablelist
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[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
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`traits_type::is_unbounded() || ( sctx.size <= traits_type::maximum_size() )`.]]
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[[Effects:] [Deallocates the stack space.]]
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]
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[class_heading pooled_fixedsize_stack]
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__boost_fiber__ provides the class __ofixedsize_stack__ which models
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the __stack_allocator_concept__.
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In contrast to __pfixedsize_stack__ it does not append a guard page at the
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end of each stack. The memory is managed internally by
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[@http://www.boost.org/doc/libs/release/libs/pool/doc/html/boost/pool.html `boost::pool<>`].
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#include <boost/fiber/pooled_fixedsize_stack.hpp>
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namespace boost {
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namespace fibers {
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struct pooled_fixedsize_stack {
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pooled_fixedsize_stack(std::size_t stack_size = traits_type::default_size(), std::size_t next_size = 32, std::size_t max_size = 0);
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stack_context allocate();
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void deallocate( stack_context &);
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}
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}}
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[hding pooled_fixedsize..Constructor]
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pooled_fixedsize_stack(std::size_t stack_size, std::size_t next_size, std::size_t max_size);
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[variablelist
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[[Preconditions:] [`traits_type::is_unbounded() || ( traits_type::maximum_size() >= stack_size)`
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and `0 < next_size`.]]
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[[Effects:] [Allocates memory of at least `stack_size` bytes and stores a pointer to
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the stack and its actual size in `sctx`. Depending on the architecture (the
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stack grows downwards/upwards) the stored address is the highest/lowest
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address of the stack. Argument `next_size` determines the number of stacks to
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request from the system the first time that `*this` needs to allocate system
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memory. The third argument `max_size` controls how much memory might be
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allocated for stacks [mdash] a value of zero means no upper limit.]]
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]
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[member_heading pooled_fixedsize..allocate]
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stack_context allocate();
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[variablelist
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[[Preconditions:] [`traits_type::is_unbounded() || ( traits_type::maximum_size() >= stack_size)`.]]
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[[Effects:] [Allocates memory of at least `stack_size` bytes and stores a pointer to
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the stack and its actual size in `sctx`. Depending on the architecture (the
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stack grows downwards/upwards) the stored address is the highest/lowest
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address of the stack.]]
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]
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[member_heading pooled_fixesize..deallocate]
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void deallocate( stack_context & sctx);
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[variablelist
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[[Preconditions:] [`sctx.sp` is valid,
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`traits_type::is_unbounded() || ( traits_type::maximum_size() >= sctx.size)`.]]
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[[Effects:] [Deallocates the stack space.]]
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]
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[note This stack allocator is not thread safe.]
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[class_heading fixedsize_stack]
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__boost_fiber__ provides the class __fixedsize_stack__ which models
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the __stack_allocator_concept__.
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In contrast to __pfixedsize_stack__ it does not append a guard page at the
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end of each stack. The memory is simply managed by `std::malloc()` and
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`std::free()`.
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#include <boost/context/fixedsize_stack.hpp>
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namespace boost {
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namespace fibers {
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struct fixedsize_stack {
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fixedsize_stack(std::size_t size = traits_type::default_size());
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stack_context allocate();
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void deallocate( stack_context &);
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}
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}}
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[member_heading fixedsize..allocate]
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stack_context allocate();
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[variablelist
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[[Preconditions:] [`traits_type::minimum_size() <= size` and
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`traits_type::is_unbounded() || ( traits_type::maximum_size() >= size)`.]]
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[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer to
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the stack and its actual size in `sctx`. Depending on the architecture (the
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stack grows downwards/upwards) the stored address is the highest/lowest
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address of the stack.]]
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]
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[member_heading fixesize..deallocate]
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void deallocate( stack_context & sctx);
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[variablelist
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[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
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`traits_type::is_unbounded() || ( traits_type::maximum_size() >= sctx.size)`.]]
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[[Effects:] [Deallocates the stack space.]]
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]
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[#segmented]
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[class_heading segmented_stack]
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__boost_fiber__ supports usage of a __segmented_stack__, i.e.
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the stack grows on demand. The fiber is created with a minimal stack size
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which will be increased as required.
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Class __segmented_stack__ models the __stack_allocator_concept__.
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In contrast to __pfixedsize_stack__ and __fixedsize_stack__ it creates a
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stack which grows on demand.
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[note Segmented stacks are currently only supported by [*gcc] from version
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[*4.7] and [*clang] from version [*3.4] onwards. In order to use a
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__segmented_stack__ __boost_fiber__ must be built with
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property `segmented-stacks`, e.g. [*toolset=gcc segmented-stacks=on]
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and applying BOOST_USE_SEGMENTED_STACKS at b2/bjam command line.]
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[note Segmented stacks can only be used with callcc() using property
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`context-impl=ucontext`.]
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#include <boost/fiber/segmented_stack.hpp>
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namespace boost {
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namespace fibers {
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struct segmented_stack {
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segmented_stack(std::size_t stack_size = traits_type::default_size());
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stack_context allocate();
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void deallocate( stack_context &);
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}
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}}
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[member_heading segmented..allocate]
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stack_context allocate();
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[variablelist
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[[Preconditions:] [`traits_type::minimum_size() <= size` and
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`traits_type::is_unbounded() || ( traits_type::maximum_size() >= size)`.]]
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[[Effects:] [Allocates memory of at least `size` bytes and stores a pointer to
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the stack and its actual size in `sctx`. Depending on the architecture (the
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stack grows downwards/upwards) the stored address is the highest/lowest
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address of the stack.]]
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]
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[member_heading segmented..deallocate]
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void deallocate( stack_context & sctx);
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[variablelist
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[[Preconditions:] [`sctx.sp` is valid, `traits_type::minimum_size() <= sctx.size` and
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`traits_type::is_unbounded() || ( traits_type::maximum_size() >= sctx.size)`.]]
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[[Effects:] [Deallocates the stack space.]]
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]
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[note If the library is compiled for segmented stacks, __segmented_stack__ is the only
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available stack allocator.]
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[section:valgrind Support for valgrind]
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Running programs that switch stacks under valgrind causes problems.
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Property (b2 command-line) `valgrind=on` let valgrind treat the memory regions
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as stack space which suppresses the errors.
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[endsect]
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[section:sanitizers Support for sanitizers]
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Sanitizers (GCC/Clang) are confused by the stack switches.
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The library (and Boost.Context too) is required to be compiled with property (b2 command-line)
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`context-impl=ucontext` and compilers santizer options.
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Users must define `BOOST_USE_ASAN` before including any Boost.Context headers
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when linking against Boost binaries.
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[endsect]
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[endsect]
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