RFC: deprecate readsfrom/writesto in favor of simply using open on AbstractCmd

NEWS.md

@@ -339,6 +339,8 @@ Deprecated or removed
 
   * `bitmix` is replaced by a 2-argument form of `hash`.
 
+  * `readsfrom` and `writesto` are replaced by `open` ([#6948]).
+
 [#4042]: https://github.com/JuliaLang/julia/issues/4042
 [#5164]: https://github.com/JuliaLang/julia/issues/5164
 [#4026]: https://github.com/JuliaLang/julia/issues/4026

base/deprecated.jl

@@ -446,6 +446,9 @@ Set{T<:Number}(xs::T...) = Set{T}(xs)
 @deprecate bitmix(x, y::Union(Uint32, Int32)) convert(Uint32, hash(x, uint(y)))
 @deprecate bitmix(x, y::Union(Uint64, Int64)) convert(Uint64, hash(x, hash(y)))
 
+@deprecate readsfrom(cmd, args...)      open(cmd, "r", args...)
+@deprecate writesto(cmd, args...)      open(cmd, "w", args...)
+
 # 0.3 discontinued functions
 
 function nnz(X)

base/exports.jl

@@ -1258,12 +1258,10 @@ export
     process_exited,
     process_running,
     readandwrite,
-    readsfrom,
     run,
     setenv,
     spawn,
     success,
-    writesto,
 
 # C interface
     c_free,

base/interactiveutil.jl

@@ -66,10 +66,9 @@ end
 
 @osx_only begin
     function clipboard(x)
-        w,p = writesto(`pbcopy`)
-        print(w,x)
-        close(w)
-        wait(p)
+        open(`pbcopy`, "w") do io
+            print(io, x)
+        end
     end
     clipboard() = readall(`pbpaste`)
 end
@@ -89,10 +88,9 @@ end
         cmd = c == :xsel  ? `xsel --nodetach --input --clipboard` :
               c == :xclip ? `xclip -quiet -in -selection clipboard` :
             error("unexpected clipboard command: $c")
-        w,p = writesto(cmd)
-        print(w,x)
-        close(w)
-        wait(p)
+        open(cmd, "w") do io
+            print(io, x)
+        end
     end
     function clipboard()
         c = clipboardcmd()

base/multi.jl

@@ -1118,7 +1118,7 @@ function launch_local_workers(cman::LocalManager, np::Integer, config::Dict)
 
     # start the processes first...
     for i in 1:np
-        io, pobj = readsfrom(detach(`$(dir)/$(exename) --bind-to $(LPROC.bind_addr) $exeflags`))
+        io, pobj = open(detach(`$(dir)/$(exename) --bind-to $(LPROC.bind_addr) $exeflags`), "r")
         io_objs[i] = io
         configs[i] = merge(config, {:process => pobj})
     end
@@ -1175,7 +1175,7 @@ function launch_ssh_workers(cman::SSHManager, np::Integer, config::Dict)
         cmd = `sh -l -c $(shell_escape(cmd))`                   # shell to launch under
         cmd = `ssh -n $sshflags $host $(shell_escape(cmd))`     # use ssh to remote launch
 
-        io, pobj = readsfrom(detach(cmd))
+        io, pobj = open(detach(cmd), "r")
         io_objs[i] = io
         configs[i] = merge(config, {:machine => cman.machines[i]})
     end

base/process.jl

@@ -418,30 +418,43 @@ function eachline(cmd::AbstractCmd,stdin)
 end
 eachline(cmd::AbstractCmd) = eachline(cmd,DevNull)
 
-#returns a pipe to read from the last command in the pipelines
-readsfrom(cmds::AbstractCmd) = readsfrom(cmds, DevNull)
-function readsfrom(cmds::AbstractCmd, stdin::AsyncStream)
-    processes = @tmp_rpipe out tmp spawn(false, cmds, (stdin,tmp,STDERR))
-    start_reading(out)
-    (out, processes)
+# return a (Pipe,Process) pair to write/read to/from the pipeline
+function open(cmds::AbstractCmd, mode::String="r", stdio::AsyncStream=DevNull)
+    if mode == "r"
+        processes = @tmp_rpipe out tmp spawn(false, cmds, (stdio,tmp,STDERR))
+        start_reading(out)
+        (out, processes)
+    elseif mode == "w"
+        processes = @tmp_wpipe tmp inpipe spawn(false,cmds, (tmp,stdio,STDERR))
+        (inpipe, processes)
+    else
+        throw(ArgumentError("mode must be \"r\" or \"w\", not \"$mode\""))
+    end
 end
 
-function writesto(cmds::AbstractCmd, stdout::UVStream)
-    processes = @tmp_wpipe tmp inpipe spawn(false, cmds, (tmp,stdout,STDERR))
-    (inpipe, processes)
+function open(f::Function, cmds::AbstractCmd, args...)
+    io, P = open(cmds, args...)
+    ret = try
+        f(io)
+    catch
+        kill(P)
+        rethrow()
+    finally
+        close(io)
+    end
+    success(P) || pipeline_error(P)
+    return ret
 end
-writesto(cmds::AbstractCmd) = writesto(cmds, DevNull)
 
+# TODO: convert this to use open(cmd, "r+"), with a single read/write pipe
 function readandwrite(cmds::AbstractCmd)
-    (out, processes) = @tmp_wpipe tmp inpipe readsfrom(cmds, tmp)
+    (out, processes) = @tmp_wpipe tmp inpipe open(cmds, "r", tmp)
     (out, inpipe, processes)
 end
 
 function readbytes(cmd::AbstractCmd, stdin::AsyncStream=DevNull)
-    (out,pc) = readsfrom(cmd, stdin)
-    if !success(pc)
-        pipeline_error(pc)
-    end
+    (out,pc) = open(cmd, "r", stdin)
+    !success(pc) && pipeline_error(P)
     wait_close(out)
     return takebuf_array(out.buffer)
 end
@@ -450,15 +463,10 @@ function readall(cmd::AbstractCmd, stdin::AsyncStream=DevNull)
     return bytestring(readbytes(cmd, stdin))
 end
 
-writeall(cmd::AbstractCmd, stdin::String) = writeall(cmd, stdin, DevNull)
-function writeall(cmd::AbstractCmd, stdin::String, stdout::AsyncStream)
-    (in,pc) = writesto(cmd, stdout)
-    write(in, stdin)
-    close(in)
-    if !success(pc)
-        pipeline_error(pc)
+function writeall(cmd::AbstractCmd, stdin::String, stdout::AsyncStream=DevNull)
+    open(cmd, "w", stdout) do io
+        write(io, stdin)
     end
-    return true
 end
 
 function run(cmds::AbstractCmd,args...)

base/sharedarray.jl

@@ -317,9 +317,9 @@ function print_shmem_limits(slen)
         @linux_only pfx = "kernel"
         @osx_only pfx = "kern.sysv"
 
-        shmmax_MB = div(int(split(readall(readsfrom(`sysctl $(pfx).shmmax`)[1]))[end]), 1024*1024)
-        page_size = int(split(readall(readsfrom(`getconf PAGE_SIZE`)[1]))[end])
-        shmall_MB = div(int(split(readall(readsfrom(`sysctl $(pfx).shmall`)[1]))[end]) * page_size, 1024*1024)
+        shmmax_MB = div(int(split(readall(`sysctl $(pfx).shmmax`))[end]), 1024*1024)
+        page_size = int(split(readall(`getconf PAGE_SIZE`))[end])
+        shmall_MB = div(int(split(readall(`sysctl $(pfx).shmall`))[end]) * page_size, 1024*1024)
 
         println("System max size of single shmem segment(MB) : ", shmmax_MB,
             "\nSystem max size of all shmem segments(MB) : ", shmall_MB,

doc/manual/running-external-programs.rst

@@ -47,6 +47,15 @@ can be used instead::
     julia> (chomp(a)) == "hello"
     true
 
+More generally, you can use ``open`` to read from or write to an external
+command.  For example:
+
+    julia> open(`less`, "w", STDOUT) do io
+               for i = 1:1000
+                   println(io, i)
+               end
+           end
+
 .. _man-command-interpolation:
 
 Interpolation

doc/stdlib/base.rst

@@ -4949,13 +4949,22 @@ System
 
    Send a signal to a process. The default is to terminate the process.
 
-.. function:: readsfrom(command)
-
-   Starts running a command asynchronously, and returns a tuple (stream,process). The first value is a stream reading from the process' standard output.
-
-.. function:: writesto(command)
-
-   Starts running a command asynchronously, and returns a tuple (stream,process). The first value is a stream writing to the process' standard input.
+.. function:: open(command, mode::String="r", stdio=DevNull)
+
+   Start running ``command`` asynchronously, and return a tuple
+   ``(stream,process)``.  If ``mode`` is ``"r"``, then ``stream``
+   reads from the process's standard output and ``stdio`` optionally
+   specifies the process's standard input stream.  If ``mode`` is
+   ``"w"``, then ``stream`` writes to the process's standard input
+   and ``stdio`` optionally specifies the process's standard output
+   stream.
+
+.. function:: open(f::Function, command, mode::String="r", stdio=DevNull)
+
+   Similar to ``open(command, mode, stdio)``, but calls ``f(stream)``
+   on the resulting read or write stream, then closes the stream
+   and waits for the process to complete.  Returns the value returned
+   by ``f``.
 
 .. function:: readandwrite(command)
 

test/spawn.jl

@@ -65,6 +65,7 @@ end
 file = tempname()
 run(`echo hello world` |> file)
 @test readall(file |> `cat`) == "hello world\n"
+@test open(readall, file |> `cat`, "r") == "hello world\n"
 rm(file)
 
 # Stream Redirection
@@ -99,9 +100,9 @@ str2 = readall(stdout)
 
 # This test hangs if the end of run walk across uv streams calls shutdown on a stream that is shutting down.
 file = tempname()
-stdin, proc = writesto(`cat -` |> file)
-write(stdin, str)
-close(stdin)
+open(`cat -` |> file, "w") do io
+    write(io, str)
+end
 rm(file)
 
 # issue #3373