20a114cb62
This adds a way to periodically pool the PAL to see if any timers have expired. Timers can be used to periodically provide callbacks to the rest of snmalloc.
97 lines
2.9 KiB
C++
97 lines
2.9 KiB
C++
#pragma once
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#include "../ds/defines.h"
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#include <atomic>
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#include <functional>
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namespace snmalloc
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{
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/**
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* Pal implementations should query this flag to see whether they
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* are allowed to optimise memory access, or that they must provide
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* exceptions/segfaults if accesses do not obey the
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* - using
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* - using_readonly
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* - not_using
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* model.
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*
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* TODO: There is a known bug in CheriBSD that means round-tripping through
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* PROT_NONE sheds capability load and store permissions (while restoring data
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* read/write, for added excitement). For the moment, just force this down on
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* CHERI.
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*/
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#if defined(SNMALLOC_CHECK_CLIENT) && !defined(__CHERI_PURE_CAPABILITY__)
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static constexpr bool PalEnforceAccess = true;
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#else
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static constexpr bool PalEnforceAccess = false;
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#endif
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/**
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* Flags in a bitfield of optional features that a PAL may support. These
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* should be set in the PAL's `pal_features` static constexpr field.
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*/
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enum PalFeatures : uint64_t
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{
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/**
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* This PAL supports low memory notifications. It must implement a
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* `register_for_low_memory_callback` method that allows callbacks to be
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* registered when the platform detects low-memory and an
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* `expensive_low_memory_check()` method that returns a `bool` indicating
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* whether low memory conditions are still in effect.
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*/
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LowMemoryNotification = (1 << 0),
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/**
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* This PAL natively supports allocation with a guaranteed alignment. If
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* this is not supported, then we will over-allocate and round the
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* allocation.
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*
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* A PAL that does supports this must expose a `request()` method that takes
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* a size and alignment. A PAL that does *not* support it must expose a
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* `request()` method that takes only a size.
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*/
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AlignedAllocation = (1 << 1),
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/**
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* This PAL natively supports lazy commit of pages. This means have large
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* allocations and not touching them does not increase memory usage. This is
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* exposed in the Pal.
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*/
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LazyCommit = (1 << 2),
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/**
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* This Pal does not support allocation. All memory used with this Pal
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* should be pre-allocated.
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*/
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NoAllocation = (1 << 3),
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/**
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* This Pal provides a source of Entropy
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*/
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Entropy = (1 << 4),
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};
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/**
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* Flag indicating whether requested memory should be zeroed.
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*/
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enum ZeroMem
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{
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/**
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* Memory should not be zeroed, contents are undefined.
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*/
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NoZero,
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/**
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* Memory must be zeroed. This can be lazily allocated via a copy-on-write
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* mechanism as long as any load from the memory returns zero.
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*/
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YesZero
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};
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/**
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* Default Tag ID for the Apple class
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*/
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static const int PALAnonDefaultID = 241;
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/**
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* Query whether the PAL supports a specific feature.
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*/
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template<PalFeatures F, typename PAL>
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constexpr static bool pal_supports = (PAL::pal_features & F) == F;
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} // namespace snmalloc
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