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Fix data race in Channel.trySend/tryRecv (issue #23174) #25359

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Fix data race in Channel.trySend/tryRecv (issue #23174) #25359

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16 changes: 9 additions & 7 deletions lib/system/channels_builtin.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -349,9 +349,11 @@ template lockChannel(q, action): untyped =
releaseSys(q.lock)

proc sendImpl(q: PRawChannel, typ: PNimType, msg: pointer, noBlock: bool): bool =
acquireSys(q.lock)
# Check mask inside the lock to avoid data race
if q.mask == ChannelDeadMask:
releaseSys(q.lock)
sysFatal(DeadThreadDefect, "cannot send message; thread died")
acquireSys(q.lock)
if q.maxItems > 0:
# Wait until count is less than maxItems
if noBlock and q.count >= q.maxItems:
Expand Down Expand Up @@ -430,12 +432,12 @@ proc tryRecv*[TMsg](c: var Channel[TMsg]): tuple[dataAvailable: bool,
## returns `(true, msg)`.
result = default(tuple[dataAvailable: bool, msg: TMsg])
var q = cast[PRawChannel](addr(c))
if q.mask != ChannelDeadMask:
if tryAcquireSys(q.lock):
if q.count > 0:
llRecv(q, addr(result.msg), cast[PNimType](getTypeInfo(result.msg)))
result.dataAvailable = true
releaseSys(q.lock)
if tryAcquireSys(q.lock):
# Check mask inside the lock to avoid data race
if q.mask != ChannelDeadMask and q.count > 0:
llRecv(q, addr(result.msg), cast[PNimType](getTypeInfo(result.msg)))
result.dataAvailable = true
releaseSys(q.lock)

proc peek*[TMsg](c: var Channel[TMsg]): int =
## Returns the current number of messages in the channel `c`.
Expand Down