wasmtime/runtime/vm/instance/allocator/pooling/
gc_heap_pool.rs

1use super::GcHeapAllocationIndex;
2use super::index_allocator::{SimpleIndexAllocator, SlotId};
3use crate::runtime::vm::{GcHeap, GcRuntime, PoolingInstanceAllocatorConfig, Result};
4use crate::vm::{Memory, MemoryAllocationIndex};
5use crate::{Engine, prelude::*};
6use std::sync::Mutex;
7
8enum HeapSlot {
9    /// The is available for use, and we may or may not have lazily allocated
10    /// its associated GC heap yet.
11    Free(Option<Box<dyn GcHeap>>),
12
13    /// The slot's heap is currently in use, and it is backed by this memory
14    /// allocation index.
15    InUse(MemoryAllocationIndex),
16}
17
18impl HeapSlot {
19    fn alloc(&mut self, memory_alloc_index: MemoryAllocationIndex) -> Option<Box<dyn GcHeap>> {
20        match self {
21            HeapSlot::Free(gc_heap) => {
22                let gc_heap = gc_heap.take();
23                *self = HeapSlot::InUse(memory_alloc_index);
24                gc_heap
25            }
26            HeapSlot::InUse(_) => panic!("already in use"),
27        }
28    }
29
30    fn dealloc(&mut self, heap: Box<dyn GcHeap>) -> MemoryAllocationIndex {
31        match *self {
32            HeapSlot::Free(_) => panic!("already free"),
33            HeapSlot::InUse(memory_alloc_index) => {
34                *self = HeapSlot::Free(Some(heap));
35                memory_alloc_index
36            }
37        }
38    }
39}
40
41/// A pool of reusable GC heaps.
42pub struct GcHeapPool {
43    max_gc_heaps: usize,
44    index_allocator: SimpleIndexAllocator,
45    heaps: Mutex<Box<[HeapSlot]>>,
46}
47
48impl std::fmt::Debug for GcHeapPool {
49    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
50        f.debug_struct("GcHeapPool")
51            .field("max_gc_heaps", &self.max_gc_heaps)
52            .field("index_allocator", &self.index_allocator)
53            .field("heaps", &"..")
54            .finish()
55    }
56}
57
58impl GcHeapPool {
59    /// Create a new `GcHeapPool` with the given configuration.
60    pub fn new(config: &PoolingInstanceAllocatorConfig) -> Result<Self> {
61        let index_allocator = SimpleIndexAllocator::new(config.limits.total_gc_heaps);
62        let max_gc_heaps = usize::try_from(config.limits.total_gc_heaps).unwrap();
63
64        // Each individual GC heap in the pool is lazily allocated. See the
65        // `allocate` method.
66        let heaps = Mutex::new((0..max_gc_heaps).map(|_| HeapSlot::Free(None)).collect());
67
68        Ok(Self {
69            max_gc_heaps,
70            index_allocator,
71            heaps,
72        })
73    }
74
75    /// Are there zero slots in use right now?
76    pub fn is_empty(&self) -> bool {
77        self.index_allocator.is_empty()
78    }
79
80    /// Allocate a single table for the given instance allocation request.
81    pub fn allocate(
82        &self,
83        engine: &Engine,
84        gc_runtime: &dyn GcRuntime,
85        memory_alloc_index: MemoryAllocationIndex,
86        memory: Memory,
87    ) -> Result<(GcHeapAllocationIndex, Box<dyn GcHeap>)> {
88        let allocation_index = self
89            .index_allocator
90            .alloc()
91            .map(|slot| GcHeapAllocationIndex(slot.0))
92            .ok_or_else(|| {
93                anyhow!(
94                    "maximum concurrent GC heap limit of {} reached",
95                    self.max_gc_heaps
96                )
97            })?;
98        debug_assert_ne!(allocation_index, GcHeapAllocationIndex::default());
99
100        let mut heap = match {
101            let mut heaps = self.heaps.lock().unwrap();
102            heaps[allocation_index.index()].alloc(memory_alloc_index)
103        } {
104            // If we already have a heap at this slot, reuse it.
105            Some(heap) => heap,
106            // Otherwise, we haven't forced this slot's lazily allocated heap
107            // yet. So do that now.
108            None => gc_runtime.new_gc_heap(engine)?,
109        };
110
111        debug_assert!(!heap.is_attached());
112        heap.attach(memory);
113
114        Ok((allocation_index, heap))
115    }
116
117    /// Deallocate a previously-allocated GC heap.
118    pub fn deallocate(
119        &self,
120        allocation_index: GcHeapAllocationIndex,
121        mut heap: Box<dyn GcHeap>,
122    ) -> (MemoryAllocationIndex, Memory) {
123        debug_assert_ne!(allocation_index, GcHeapAllocationIndex::default());
124
125        let memory = heap.detach();
126
127        // NB: Replace the heap before freeing the index. If we did it in the
128        // opposite order, a concurrent allocation request could reallocate the
129        // index before we have replaced the heap.
130
131        let memory_alloc_index = {
132            let mut heaps = self.heaps.lock().unwrap();
133            heaps[allocation_index.index()].dealloc(heap)
134        };
135
136        self.index_allocator.free(SlotId(allocation_index.0));
137
138        (memory_alloc_index, memory)
139    }
140}
wasmtime/runtime/vm/instance/allocator/pooling/gc_heap_pool.rs

wasmtime/runtime/vm/instance/allocator/pooling/
gc_heap_pool.rs
