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* WebAssembly threads: fixed race condition LockMutex in the check where Locked

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is 1, but Owner still holds the current thread id, even though another thread
  has just acquired a lock, but still haven't updated the owner thread ID. We
  avoid this problem by setting Owner to nil before unlocking the mutex. And in
  InitMutex/DoneMutex, we store the creator thread ID in a different field -
  Creator, instead of Owner.
This commit is contained in:
Nikolay Nikolov 2024-08-03 02:34:00 +03:00
parent 692bd62359
commit 41ead20bfb
2 changed files with 5 additions and 3 deletions
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3
rtl/wasi/sysosh.inc
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@ -27,6 +27,7 @@ type
Count: LongInt; // Number of times locked.
Waiters : LongInt; // Number of waiters
Kind : LongInt; // Kind of mutex, Equals Ord(TMutexKind)
Owner : TThreadID; // Owner thread
Owner : TThreadID; // Owner thread (who holds the lock)
Creator : TThreadID; // Creator thread
Destroying : Boolean; // Set when notifying that we're destroying the mutex.
end;

5
rtl/wasi/wasmmutex.inc
View File

@ -20,7 +20,7 @@ begin
FillChar(M,SizeOf(TWasmMutex),0);
if aOwner=Nil then
aOwner:=GetSelfThread;
M.Owner:=aOwner;
M.Creator:=aOwner;
M.Kind:=Ord(aKind);
end;
@ -30,7 +30,7 @@ Var
a : LongInt;
begin
if (M.Locked>0) and (M.Owner=GetSelfThread) then
if (M.Locked>0) and (M.Creator=GetSelfThread) then
begin
M.Destroying:=True;
a:=fpc_wasm32_memory_atomic_notify(@M.Locked,MaxThreadSignal);
@ -190,6 +190,7 @@ begin
InterLockedDecrement(M.Count);
if (M.Count=0) then
begin
M.Owner:=nil;
M.Locked:=0;
a:=fpc_wasm32_memory_atomic_notify(@M.Locked,1);
end;