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fix(library): block first-time callers until NimMain completes

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initializeLibrary ran NimMain only on the thread that won
`initialized.exchange(true)`; concurrent first-time callers fell straight
through and used a half-initialized Nim runtime — a heap-corrupting race
when multiple foreign (e.g. Go) threads create the first context at once.
Add an `initDone` flag the winner sets after NimMain; the others spin
until it is set before proceeding.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Ivan FB 2026-06-18 20:11:39 +02:00
parent 342fefa623
commit e22b887d7c
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GPG Key ID: DF0C67A04C543270
1 changed files with 12 additions and 2 deletions
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14
ffi/internal/ffi_library.nim
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@ -53,10 +53,13 @@ macro declareLibraryBase*(libraryName: static[string]): untyped =
)
res.add(procDef)
# Create: var initialized: Atomic[bool]
# Create: var initialized, initDone: Atomic[bool]
# `initialized` elects the single thread that runs NimMain; `initDone` signals
# that NimMain has finished so concurrent first-time callers can safely proceed.
let atomicType = nnkBracketExpr.newTree(ident("Atomic"), ident("bool"))
let varStmt = nnkVarSection.newTree(
nnkIdentDefs.newTree(ident("initialized"), atomicType, newEmptyNode())
nnkIdentDefs.newTree(ident("initialized"), atomicType, newEmptyNode()),
nnkIdentDefs.newTree(ident("initDone"), atomicType, newEmptyNode()),
)
res.add(varStmt)
@ -80,6 +83,13 @@ macro declareLibraryBase*(libraryName: static[string]): untyped =
## Being `<yourprefix>` the value given in the optional
## compilation flag --nimMainPrefix:yourprefix
`nimMainName`()
initDone.store(true)
else:
## Another thread won the election and is running (or has run) NimMain.
## Block until it finishes: proceeding now would race a half-initialized
## Nim runtime/GC and corrupt the heap on concurrent first-time calls.
while not initDone.load():
discard
when declared(setupForeignThreadGc):
setupForeignThreadGc()
when declared(nimGC_setStackBottom):