Make write_env_usage atomic

src/Types.jl

@@ -459,20 +459,60 @@ end
 function write_env_usage(source_file::AbstractString, usage_filepath::AbstractString)
     # Don't record ghost usage
     !isfile(source_file) && return
-
     # Ensure that log dir exists
     !ispath(logdir()) && mkpath(logdir())
 
-    # Generate entire entry as a string first
-    entry = sprint() do io
-        TOML.print(io, Dict(source_file => [Dict("time" => now())]))
-    end
-
-    # Append entry to log file in one chunk
+    p = TOML.Parser()
     usage_file = joinpath(logdir(), usage_filepath)
-    open(usage_file, append=true) do io
-        write(io, entry)
+    timestamp = now()
+
+    ## Atomically write usage file
+    while true
+        # read existing usage file
+        usage = if isfile(usage_file)
+            content = read(usage_file)
+            Base.TOML.reinit!(p, String(content); filepath=usage_file)
+            Base.TOML.parse(p)
+        else
+            Dict()
+        end
+
+        # record new usage
+        usage[source_file] = [Dict("time" => timestamp)]
+
+        # keep only latest usage info
+        for kv in usage
+            times = map(d->Dates.DateTime(d["time"]), usage[kv.first])
+            usage[kv.first] = [Dict("time" => maximum(times))]
+        end
+
+        # Write to a temp file in the same directory as the destination
+        temp_usage_file = tempname(logdir())
+        open(temp_usage_file, "w") do io
+            TOML.print(io, usage, sorted=true)
+        end
+
+        # Move the temp file into place, replacing the original
+        mv(temp_usage_file, usage_file, force = true)
+
+        # Check that the new file has what we want in it
+        new_usage = if isfile(usage_file)
+            content = read(usage_file)
+            Base.TOML.reinit!(p, String(content); filepath=usage_file)
+            Base.TOML.parse(p)
+        else
+            Dict()
+        end
+        if haskey(new_usage, source_file)
+            for e in new_usage[source_file]
+                if Dates.DateTime(e["time"]) >= timestamp
+                    return
+                end
+            end
+        end
+        # If not, try again
     end
+
 end
 
 function read_package(path::String)