39 lines
1.6 KiB
ReStructuredText
39 lines
1.6 KiB
ReStructuredText
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=====================================
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Pool allocator for low memory targets
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=====================================
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A simple pool allocator which satisfies allocations from preallocated pools
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containing blocks of a certain size. The caller provides a continuous memory
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region and a pool configuration when initializing the allocator.
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The pool configuration specifies the block sizes used, and parameters to
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control how many entries are allocated for each block size. The parameters
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are specified with respect to an arbitrary floating point scaling parameter
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``t`` as follows::
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bytes = A*t + B
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count = floor(bytes / block_size)
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= floor((A*t + B) / block_size)
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A: constant which indicates how quickly more bytes are assigned for this
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block size as the total allocation grows
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B: constant which indicates the base allocation for this block size, i.e.
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the allocated needed by Duktape initialization
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Pool initialization finds the largest floating point ``t`` which still fits in
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the memory region provided. Any leftover bytes are sprinkled to the pools to
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minimize wasted space.
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A pool configuration can be written manually (by trial and error) or using
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some automatic tooling such as ``pool_simulator.py``.
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When using pointer compression only a single global pool is supported. This
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reduces code footprint and is usually sufficient in low memory targets.
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Pointer compression functions are defined as inline functions in
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``duk_alloc_pool.h`` to allow the compiler to inline pointer compression when
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appropriate. As a side effect ``duk_config.h`` must include
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``duk_alloc_pool.h`` so that the declarations are visible when compiling
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Duktape.
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