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Add threadLock keyword -- locks mutex, evals code, then unlocks #3749

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Add threadLock keyword -- locks mutex, evals code, then unlocks #3749

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1 change: 1 addition & 0 deletions M2/Macaulay2/d/binding.d
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Expand Up @@ -318,6 +318,7 @@ bumpPrecedence();
export breakpointS := special("breakpoint", unaryop, precSpace, wide);
export profileS := special("profile", unaryop, precSpace, wide);
export shieldS := special("shield", unaryop, precSpace, wide);
export threadLockS := special("threadLock", unaryop, precSpace, wide);
export throwS := special("throw", nunaryop, precSpace, wide);
export returnS := special("return", nunaryop, precSpace, wide);
export breakS := special("break", nunaryop, precSpace, wide);
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15 changes: 15 additions & 0 deletions M2/Macaulay2/d/pthread.d
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Expand Up @@ -3,6 +3,7 @@ use evaluate;
use expr;

header "#include \"../system/supervisorinterface.h\"";
header "#include <errno.h>"; -- for EBUSY


taskCreatePush(f:function(TaskCellBody):null,tb:TaskCellBody) ::= Ccode(taskPointer,
Expand Down Expand Up @@ -231,6 +232,20 @@ export getIOThreadMode(e:Expr):Expr := (
else WrongArg("a file or ()"));
setupfun("getIOThreadMode", getIOThreadMode);

-- TODO: what if we cancel a task before it unlocks the mutex?
mutex := newMutex;
threadLock(c:Code):Expr := (
r := 0;
while (r = trylock(mutex); r == Ccode(int, "EBUSY")) do (
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This is not good. I think you want pthread_cond_wait or similar.

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From what I've read, pthread_mutex_trylock is the only way to check if a mutex is locked. pthread_cond_wait blocks until some condition is met, and we don't want to block since we want to check for interrupts.

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I definitely think we need pthread conditions, because you can signal only one or all threads using pthread_cond_signal and pthread_cond_broadcast that an event has changed. This is how tasks are implemented too. e.g. this is how taskResult blocks:

M2/M2/Macaulay2/system/supervisor.cpp

Lines 210 to 215 in 2565455

lock_guard<pthreadMutex> lock(m_Mutex);
while(!m_Done && m_KeepRunning)
{
pthread_cond_wait(&m_FinishCondition,&m_Mutex.m_Mutex);
}
return m_Result;

In fact, I suspect if we change interrupt_handler in main.cpp to also signal the current blocking task, it would interrupt just fine.

f := eval(dummyCode); -- handle interrupts
when f is Error do return f else nothing);
if r == 0 then (
e := eval(c);
unlock(mutex);
e)
else buildErrorPacketErrno("threadLock", r));
setupop(threadLockS, threadLock);

-- Local Variables:
-- compile-command: "echo \"make: Entering directory \\`$M2BUILDDIR/Macaulay2/d'\" && make -C $M2BUILDDIR/Macaulay2/d pthread.o "
-- End:
1 change: 1 addition & 0 deletions M2/Macaulay2/d/pthread0.d
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Expand Up @@ -30,6 +30,7 @@ export SpinLock := atomicType "struct spinlockStructure";
export init(x:ThreadMutex) ::= Ccode(int, "pthread_mutex_init(&(",lvalue(x),"),NULL)");
export destroy(x:ThreadMutex) ::= Ccode(int, "pthread_mutex_destroy(&(",lvalue(x),"))");
export lock(x:ThreadMutex) ::= Ccode(int, "pthread_mutex_lock(&(",lvalue(x),"))");
export trylock(x:ThreadMutex) ::= Ccode(int, "pthread_mutex_trylock(&(",lvalue(x),"))");
export unlock(x:ThreadMutex) ::= Ccode(int, "pthread_mutex_unlock(&(",lvalue(x),"))");
export getthreadself() ::= Ccode(Thread, "pthread_self()");

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1 change: 1 addition & 0 deletions M2/Macaulay2/m2/exports.m2
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Expand Up @@ -1203,6 +1203,7 @@ export {
"texMath",
"then",
"threadLocal",
"threadLock",
"throw",
"time",
"times",
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7 changes: 7 additions & 0 deletions M2/Macaulay2/tests/normal/threads.m2
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Expand Up @@ -85,6 +85,13 @@ assert Equation(getIOThreadMode f, 2)

removeFile fn

-- threadLock
-- mutable lists are *not* thread safe
-- if they ever become thread safe, then change this test
x = new MutableList
taskResult \ apply(1000, i -> schedule(() -> threadLock x##x = null));
assert Equation(#x, 1000)

-- Local Variables:
-- compile-command: "make -C $M2BUILDDIR/Macaulay2/packages/Macaulay2Doc/test threads.out"
-- End:
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