read precompile_file in real time

contrib/generate_precompile.jl

@@ -388,6 +388,7 @@ generate_precompile_statements() = try # Make sure `ansi_enablecursor` is printe
             close(output_copy)
             close(ptm)
         end
+        repl_inputter = @async begin
             # wait for the definitive prompt before start writing to the TTY
             readuntil(output_copy, JULIA_PROMPT)
             sleep(0.1)
@@ -424,12 +425,21 @@ generate_precompile_statements() = try # Make sure `ansi_enablecursor` is printe
             success(p) || Base.pipeline_error(p)
             close(ptm)
             write(debug_output, "\n#### FINISHED ####\n")
-
+        end
         n_step2 = 0
-        for statement in split(read(precompile_file, String), '\n')
+        open(precompile_file, "r") do io
+            while true
+                eof(io) && istaskdone(repl_inputter) && break
+                if bytesavailable(io) == 0
+                    sleep(0.1)
+                    continue
+                end
+                statement = readline(io) # this blocks so we can't wait on it
+                isempty(statement) && continue
                 push!(statements_step2, statement)
                 n_step2 += 1
             end
+        end
         close(statements_step2)
         print_state("step2" => "F$n_step2")
         return :ok