add invokelatest to circumvent world-age problems

NEWS.md

@@ -322,6 +322,10 @@ Library improvements
   * `logging` can now be used to redirect `info`, `warn`, and `error` messages
     either universally or on a per-module/function basis ([#16213]).
 
+  * New function `Base.invokelatest(f, args...)` to call the latest version
+    of a function in circumstances where an older version may be called
+    instead (e.g. in a function calling `eval`) ([#19784]).
+
   * A new `iszero(x)` function was added, to quickly check whether `x` is zero
     (or is all zeros, for an array) ([#19950]).
 

base/essentials.jl

@@ -337,3 +337,15 @@ function vector_any(xs::ANY...)
 end
 
 isempty(itr) = done(itr, start(itr))
+
+"""
+    invokelatest(f, args...)
+
+Calls `f(args...)`, but guarantees that the most recent method of `f`
+will be executed.   This is useful in specialized circumstances,
+e.g. long-running event loops or callback functions that may
+call obsolete versions of a function `f`.
+(The drawback is that `invokelatest` is somewhat slower than calling
+`f` directly, and the type of the result cannot be inferred by the compiler.)
+"""
+invokelatest(f, args...) = Core._apply_latest(f, args)

base/socket.jl

@@ -589,18 +589,18 @@ function uv_getaddrinfocb(req::Ptr{Void}, status::Cint, addrinfo::Ptr{Void})
     cb = unsafe_pointer_to_objref(data)::Function
     pop!(callback_dict,cb) # using pop forces an error if cb not in callback_dict
     if status != 0 || addrinfo == C_NULL
-        cb(UVError("uv_getaddrinfocb received an unexpected status code", status))
+        invokelatest(cb, UVError("uv_getaddrinfocb received an unexpected status code", status))
     else
         freeaddrinfo = addrinfo
         while addrinfo != C_NULL
             sockaddr = ccall(:jl_sockaddr_from_addrinfo, Ptr{Void}, (Ptr{Void},), addrinfo)
             if ccall(:jl_sockaddr_is_ip4, Int32, (Ptr{Void},), sockaddr) == 1
-                cb(IPv4(ntoh(ccall(:jl_sockaddr_host4, UInt32, (Ptr{Void},), sockaddr))))
+                invokelatest(cb, IPv4(ntoh(ccall(:jl_sockaddr_host4, UInt32, (Ptr{Void},), sockaddr))))
                 break
             #elseif ccall(:jl_sockaddr_is_ip6, Int32, (Ptr{Void},), sockaddr) == 1
             #    host = Vector{UInt128}(1)
             #    scope_id = ccall(:jl_sockaddr_host6, UInt32, (Ptr{Void}, Ptr{UInt128}), sockaddr, host)
-            #    cb(IPv6(ntoh(host[1])))
+            #    invokelatest(cb, IPv6(ntoh(host[1])))
             #    break
             end
             addrinfo = ccall(:jl_next_from_addrinfo, Ptr{Void}, (Ptr{Void},), addrinfo)

doc/src/manual/methods.md

@@ -455,17 +455,12 @@ In the example above, we see that the "current world" (in which the method `newf
 is one greater than the task-local "runtime world" that was fixed when the execution of `tryeval` started.
 
 Sometimes it is necessary to get around this (for example, if you are implementing the above REPL).
-Well, don't despair, since there's an easy solution: just call `eval` a second time.
-For example, here we create a zero-argument closure over `ans` and `eval` a call to it:
+Fortunately, there is an easy solution: call the function using [`Base.invokelatest`](@ref):
 
 ```jldoctest
 julia> function tryeval2()
-           ans = (@eval newfun2() = 1)
-           res = eval(Expr(:call,
-               function()
-                   return ans() + 1
-               end))
-           return res
+           @eval newfun2() = 2
+           Base.invokelatest(newfun2)
        end
 tryeval2 (generic function with 1 method)
 

doc/src/stdlib/base.md

@@ -121,6 +121,7 @@ Base.instances
 Base.method_exists
 Core.applicable
 Core.invoke
+Base.invokelatest
 Base.:(|>)
 Base.:(∘)
 ```

src/builtin_proto.h

@@ -23,6 +23,7 @@ DECLARE_BUILTIN(throw);      DECLARE_BUILTIN(is);
 DECLARE_BUILTIN(typeof);     DECLARE_BUILTIN(sizeof);
 DECLARE_BUILTIN(issubtype);  DECLARE_BUILTIN(isa);
 DECLARE_BUILTIN(_apply);     DECLARE_BUILTIN(_apply_pure);
+DECLARE_BUILTIN(_apply_latest);
 DECLARE_BUILTIN(isdefined);  DECLARE_BUILTIN(nfields);
 DECLARE_BUILTIN(tuple);      DECLARE_BUILTIN(svec);
 DECLARE_BUILTIN(getfield);   DECLARE_BUILTIN(setfield);

src/builtins.c

@@ -454,6 +454,18 @@ JL_CALLABLE(jl_f__apply_pure)
     return ret;
 }
 
+// this is like `_apply`, but always runs in the newest world
+JL_CALLABLE(jl_f__apply_latest)
+{
+    jl_ptls_t ptls = jl_get_ptls_states();
+    size_t last_age = ptls->world_age;
+    if (!ptls->in_pure_callback)
+        ptls->world_age = jl_world_counter;
+    jl_value_t *ret = jl_f__apply(NULL, args, nargs);
+    ptls->world_age = last_age;
+    return ret;
+}
+
 // eval -----------------------------------------------------------------------
 
 JL_DLLEXPORT jl_value_t *jl_toplevel_eval_in(jl_module_t *m, jl_value_t *ex)
@@ -1089,6 +1101,7 @@ void jl_init_primitives(void)
     add_builtin_func("apply_type", jl_f_apply_type);
     add_builtin_func("_apply", jl_f__apply);
     add_builtin_func("_apply_pure", jl_f__apply_pure);
+    add_builtin_func("_apply_latest", jl_f__apply_latest);
     add_builtin_func("_expr", jl_f__expr);
     add_builtin_func("svec", jl_f_svec);
 

src/codegen.cpp

@@ -6761,6 +6761,7 @@ static void init_julia_llvm_env(Module *m)
     builtin_func_map[jl_f_typeassert] = jlcall_func_to_llvm("jl_f_typeassert", &jl_f_typeassert, m);
     builtin_func_map[jl_f__apply] = jlcall_func_to_llvm("jl_f__apply", &jl_f__apply, m);
     builtin_func_map[jl_f__apply_pure] = jlcall_func_to_llvm("jl_f__apply_pure", &jl_f__apply_pure, m);
+    builtin_func_map[jl_f__apply_latest] = jlcall_func_to_llvm("jl_f__apply_latest", &jl_f__apply_latest, m);
     builtin_func_map[jl_f_throw] = jlcall_func_to_llvm("jl_f_throw", &jl_f_throw, m);
     builtin_func_map[jl_f_tuple] = jlcall_func_to_llvm("jl_f_tuple", &jl_f_tuple, m);
     builtin_func_map[jl_f_svec] = jlcall_func_to_llvm("jl_f_svec", &jl_f_svec, m);

src/dump.c

@@ -77,7 +77,7 @@ static htable_t fptr_to_id;
 static const jl_fptr_t id_to_fptrs[] = {
   NULL, NULL,
   jl_f_throw, jl_f_is, jl_f_typeof, jl_f_issubtype, jl_f_isa,
-  jl_f_typeassert, jl_f__apply, jl_f__apply_pure, jl_f_isdefined,
+  jl_f_typeassert, jl_f__apply, jl_f__apply_pure, jl_f__apply_latest, jl_f_isdefined,
   jl_f_tuple, jl_f_svec, jl_f_intrinsic_call, jl_f_invoke_kwsorter,
   jl_f_getfield, jl_f_setfield, jl_f_fieldtype, jl_f_nfields,
   jl_f_arrayref, jl_f_arrayset, jl_f_arraysize, jl_f_apply_type,

test/misc.jl

@@ -669,3 +669,12 @@ if Bool(parse(Int,(get(ENV, "JULIA_TESTFULL", "0"))))
         @test_throws StackOverflowError f_19433(+, 1, 2)
     end
 end
+
+# invokelatest function for issue #19774
+issue19774(x) = 1
+let foo() = begin
+        eval(:(issue19774(x::Int) = 2))
+        return Base.invokelatest(issue19774, 0)
+    end
+    @test foo() == 2
+end