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feat(runtime): Prevent stack overflow while collecting large lists #2248

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merged 3 commits into from
Feb 17, 2025
Merged

feat(runtime): Prevent stack overflow while collecting large lists #2248

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d6c33a3
feat(runtime): Correct garbage collection of large lists
spotandjake Feb 17, 2025
844e2dc
feat: Simplify pointer semantics
spotandjake Feb 17, 2025
3e5d820
chore: Apply suggestions from oscar code review
spotandjake Feb 17, 2025
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2 changes: 1 addition & 1 deletion compiler/test/suites/basic_functionality.re
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Original file line number Diff line number Diff line change
Expand Up @@ -377,6 +377,6 @@ describe("basic functionality", ({test, testSkip}) => {
~config_fn=smallestFileConfig,
"smallest_grain_program",
"",
6540,
6503,
);
});
16 changes: 15 additions & 1 deletion compiler/test/suites/gc.re
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Original file line number Diff line number Diff line change
Expand Up @@ -139,7 +139,7 @@ describe("garbage collection", ({test, testSkip}) => {
"OK\n",
);
assertRunGC(
"long_lists",
"medium_lists",
350,
{|
from "list" include List
Expand Down Expand Up @@ -168,6 +168,20 @@ describe("garbage collection", ({test, testSkip}) => {
|},
"true\n",
);
assertRun(
"large_lists",
{|
let rec make_list = (n, acc) => {
if (n == 0) {
acc
} else {
make_list(n - 1, [1, ...acc])
}
}
assert make_list(500_000, []) != []
|},
"",
);
assertFileRun("memory_grow1", "memoryGrow", "1000000000000\n");
assertMemoryLimitedFileRun(
"loop_memory_reclaim",
Expand Down
73 changes: 39 additions & 34 deletions stdlib/runtime/gc.gr
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Expand Up @@ -75,7 +75,7 @@ provide let incRef = (userPtr: WasmI32) => {
userPtr
}

let rec decRef = (userPtr: WasmI32, ignoreZeros: Bool) => {
let rec decRef = (userPtr: WasmI32, parentPtr: WasmI32, ignoreZeros: Bool) => {
if (WasmI32.eqz(userPtr & Tags._GRAIN_GENERIC_TAG_MASK) && userPtr != 0n) {
let refCount = getRefCount(userPtr)
// if (_DEBUG) {
Expand All @@ -85,7 +85,7 @@ let rec decRef = (userPtr: WasmI32, ignoreZeros: Bool) => {

if (WasmI32.eqz(refCount)) {
if (ignoreZeros) {
userPtr
parentPtr
} else {
throwDecRefError()
}
Expand All @@ -94,59 +94,64 @@ let rec decRef = (userPtr: WasmI32, ignoreZeros: Bool) => {
setRefCount(userPtr, refCount)

if (WasmI32.eqz(refCount)) {
decRefChildren(userPtr)
/*
* Note: We dangerously call free before decRefChildren to allow for
* tco optimization. This works because `free` only merges the
* empty blocks and does not actually zero out the memory.
*/
free(userPtr)
decRefChildren(userPtr, parentPtr)
} else {
parentPtr
}

userPtr
}
} else {
userPtr
parentPtr
}
}
and decRefChildrenHelp = (
userPtr: WasmI32,
parentPtr: WasmI32,
arityOffset: WasmI32,
offset: WasmI32,
) => {
let arity = WasmI32.load(userPtr, arityOffset)
if (arity != 0n) {
let maxOffset = (arity - 1n) * 4n
for (let mut i = 0n; WasmI32.ltU(i, maxOffset); i += 4n) {
ignore(decRef(WasmI32.load(userPtr + i, offset), parentPtr, false))
}
decRef(WasmI32.load(userPtr + maxOffset, offset), parentPtr, false)
} else {
parentPtr
}
}
and decRefChildren = (userPtr: WasmI32) => {
and decRefChildren = (userPtr: WasmI32, parentPtr: WasmI32) => {
match (WasmI32.load(userPtr, 0n)) {
t when t == Tags._GRAIN_BOXED_NUM_HEAP_TAG => {
let tag = WasmI32.load(userPtr, 4n)
if (userPtr == Tags._GRAIN_RATIONAL_BOXED_NUM_TAG) {
// decRef underlying BigInts
ignore(decRef(WasmI32.load(userPtr, 8n), false))
ignore(decRef(WasmI32.load(userPtr, 12n), false))
ignore(decRef(WasmI32.load(userPtr, 8n), parentPtr, false))
ignore(decRef(WasmI32.load(userPtr, 12n), parentPtr, false))
}
parentPtr
},
t when t == Tags._GRAIN_ADT_HEAP_TAG => {
let arity = WasmI32.load(userPtr, 16n)
let maxOffset = arity * 4n
for (let mut i = 0n; WasmI32.ltU(i, maxOffset); i += 4n) {
ignore(decRef(WasmI32.load(userPtr + i, 20n), false))
}
decRefChildrenHelp(userPtr, parentPtr, 16n, 20n)
},
t when t == Tags._GRAIN_RECORD_HEAP_TAG => {
let arity = WasmI32.load(userPtr, 12n)
let maxOffset = arity * 4n
for (let mut i = 0n; WasmI32.ltU(i, maxOffset); i += 4n) {
ignore(decRef(WasmI32.load(userPtr + i, 16n), false))
}
decRefChildrenHelp(userPtr, parentPtr, 12n, 16n)
},
t when t == Tags._GRAIN_ARRAY_HEAP_TAG || t == Tags._GRAIN_TUPLE_HEAP_TAG => {
let arity = WasmI32.load(userPtr, 4n)
let maxOffset = arity * 4n
for (let mut i = 0n; WasmI32.ltU(i, maxOffset); i += 4n) {
ignore(decRef(WasmI32.load(userPtr + i, 8n), false))
}
decRefChildrenHelp(userPtr, parentPtr, 4n, 8n)
},
t when t == Tags._GRAIN_LAMBDA_HEAP_TAG => {
let arity = WasmI32.load(userPtr, 12n)
let maxOffset = arity * 4n
for (let mut i = 0n; WasmI32.ltU(i, maxOffset); i += 4n) {
ignore(decRef(WasmI32.load(userPtr + i, 16n), false))
}
},
_ => {
// No travelsal necessary for other tags
void
decRefChildrenHelp(userPtr, parentPtr, 12n, 16n)
},
// No travelsal necessary for other tags
_ => parentPtr,
}
}

provide let decRef = userPtr => decRef(userPtr, false)
provide let decRef = userPtr => decRef(userPtr, userPtr, false)
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