add RemoteLogger for distributed logging

stdlib/Distributed/Project.toml

@@ -2,6 +2,7 @@ name = "Distributed"
 uuid = "8ba89e20-285c-5b6f-9357-94700520ee1b"
 
 [deps]
+Logging = "56ddb016-857b-54e1-b83d-db4d58db5568"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Serialization = "9e88b42a-f829-5b0c-bbe9-9e923198166b"
 Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"

stdlib/Distributed/src/Distributed.jl

@@ -99,6 +99,7 @@ hash(r::RRID, h::UInt) = hash(r.whence, hash(r.id, h))
 ==(r::RRID, s::RRID) = (r.whence==s.whence && r.id==s.id)
 
 include("clusterserialize.jl")
+include("logger.jl")
 include("cluster.jl")   # cluster setup and management, addprocs
 include("messages.jl")
 include("process_messages.jl")  # process incoming messages

stdlib/Distributed/src/cluster.jl

@@ -268,6 +268,7 @@ function start_worker(out::IO, cookie::AbstractString=readline(stdin); close_std
         # To prevent hanging processes on remote machines, newly launched workers exit if the
         # master process does not connect in time.
         check_master_connect()
+        Logging.global_logger(RemoteLogger(1, Logging.Info))
         while true; wait(); end
     catch err
         print(stderr, "unhandled exception on $(myid()): $(err)\nexiting.\n")

stdlib/Distributed/src/logger.jl

@@ -0,0 +1,23 @@
+import Logging
+
+struct RemoteLogger <: Logging.AbstractLogger
+    pid::Int
+    min_level::Logging.LogLevel
+end
+function RemoteLogger(pid=1)
+    RemoteLogger(pid, Logging.Info)
+end
+
+Logging.min_enabled_level(logger::RemoteLogger) = logger.min_level
+Logging.shouldlog(logger::RemoteLogger, level, _module, group, id) = true
+
+# TODO: probably should live in base/logging.jl?
+function logmsg(level::Logging.LogLevel, message, _module, _group, _id, _file, _line; kwargs...)
+    Logging.@logmsg level message _module=_module _group=_group _id=_id _file=_file _line=_line kwargs...
+end
+
+function Logging.handle_message(logger::RemoteLogger, level::Logging.LogLevel, message, _module, _group, _id,
+    _file, _line; kwargs...)
+    @nospecialize
+    remote_do(logmsg, logger.pid, level, message, _module, _group, _id, _file, _line; pid=myid(), kwargs...)
+end

stdlib/Distributed/test/distributed_exec.jl

@@ -1,6 +1,6 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-using Test, Distributed, Random, Serialization, Sockets
+using Test, Distributed, Random, Serialization, Sockets, Logging
 import Distributed: launch, manage
 
 @test cluster_cookie() isa String
@@ -1915,6 +1915,18 @@ begin
     end
 end
 
+# test logging
+w = only(addprocs(1))
+@test_logs (:info, "from pid $w") begin
+    prev_logger = global_logger(current_logger())
+    try
+        wait(@spawnat w @info("from pid $(myid())"))
+    finally
+        global_logger(prev_logger)
+    end
+end
+wait(rmprocs([w]))
+
 # Run topology tests last after removing all workers, since a given
 # cluster at any time only supports a single topology.
 rmprocs(workers())