Mark the _state field as atomic and move to proper atomics instead of llvmcall (#55502)

Author: gbaraldi

base/task.jl

@@ -156,20 +156,10 @@ const task_state_runnable = UInt8(0)
 const task_state_done     = UInt8(1)
 const task_state_failed   = UInt8(2)
 
-const _state_index = findfirst(==(:_state), fieldnames(Task))
-@eval function load_state_acquire(t)
-    # TODO: Replace this by proper atomic operations when available
-    @GC.preserve t llvmcall($("""
-        %rv = load atomic i8, i8* %0 acquire, align 8
-        ret i8 %rv
-        """), UInt8, Tuple{Ptr{UInt8}},
-        Ptr{UInt8}(pointer_from_objref(t) + fieldoffset(Task, _state_index)))
-end
-
 @inline function getproperty(t::Task, field::Symbol)
     if field === :state
         # TODO: this field name should be deprecated in 2.0
-        st = load_state_acquire(t)
+        st = @atomic :acquire t._state
         if st === task_state_runnable
             return :runnable
         elseif st === task_state_done
@@ -223,7 +213,7 @@ julia> istaskdone(b)
 true
 ```
 """
-istaskdone(t::Task) = load_state_acquire(t) !== task_state_runnable
+istaskdone(t::Task) = (@atomic :acquire t._state) !== task_state_runnable
 
 """
     istaskstarted(t::Task) -> Bool
@@ -267,7 +257,7 @@ true
 !!! compat "Julia 1.3"
     This function requires at least Julia 1.3.
 """
-istaskfailed(t::Task) = (load_state_acquire(t) === task_state_failed)
+istaskfailed(t::Task) = ((@atomic :acquire t._state) === task_state_failed)
 
 Threads.threadid(t::Task) = Int(ccall(:jl_get_task_tid, Int16, (Any,), t)+1)
 function Threads.threadpool(t::Task)

src/jltypes.c

@@ -3662,6 +3662,8 @@ void jl_init_types(void) JL_GC_DISABLED
     XX(task);
     jl_value_t *listt = jl_new_struct(jl_uniontype_type, jl_task_type, jl_nothing_type);
     jl_svecset(jl_task_type->types, 0, listt);
+    const static uint32_t task_atomicfields[1] = {0x00001000}; // Set fields 13 as atomic
+    jl_task_type->name->atomicfields = task_atomicfields;
 
     tv = jl_svec2(tvar("A"), tvar("R"));
     jl_opaque_closure_type = (jl_unionall_t*)jl_new_datatype(jl_symbol("OpaqueClosure"), core, jl_function_type, tv,

stdlib/Serialization/src/Serialization.jl

@@ -1570,11 +1570,11 @@ function deserialize(s::AbstractSerializer, ::Type{Task})
     t.storage = deserialize(s)
     state = deserialize(s)
     if state === :runnable
-        t._state = Base.task_state_runnable
+        @atomic :release t._state = Base.task_state_runnable
     elseif state === :done
-        t._state = Base.task_state_done
+        @atomic :release t._state = Base.task_state_done
     elseif state === :failed
-        t._state = Base.task_state_failed
+        @atomic :release t._state = Base.task_state_failed
     else
         @assert false
     end

test/channels.jl

@@ -382,7 +382,7 @@ end
         """error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")""", output))
     # test for invalid state in Workqueue during yield
     t = @async nothing
-    t._state = 66
+    @atomic t._state = 66
     newstderr = redirect_stderr()
     try
         errstream = @async read(newstderr[1], String)

test/core.jl

@@ -42,6 +42,7 @@ for (T, c) in (
         (DataType, [:types, :layout]),
         (Core.Memory, []),
         (Core.GenericMemoryRef, []),
+        (Task, [:_state])
     )
     @test Set((fieldname(T, i) for i in 1:fieldcount(T) if Base.isfieldatomic(T, i))) == Set(c)
 end