Merge pull request #9434 from amitmurthy/amitm/custom_connect

user defined transports

Makefile

@@ -37,6 +37,7 @@ $(build_docdir):
  @mkdir -p $@/examples
  @cp -R doc/devdocs doc/manual doc/stdlib $@
  @cp -R examples/*.jl $@/examples/
+ @cp -R examples/clustermanager $@/examples/
 
 git-submodules:
 ifneq ($(NO_GIT), 1)

NEWS.md

@@ -156,6 +156,8 @@ Library improvements
 
  * Split `Triangular` type into `UpperTriangular`, `LowerTriangular`, `UnitUpperTriagular` and `UnitLowerTriangular` ([#9779])
 
+ * ClusterManager - Performance improvements([#9309]) and support for changing transports([#9434])
+
 Deprecated or removed
 ---------------------
 

base/client.jl

@@ -222,8 +222,15 @@ function process_options(args::Vector{UTF8String})
  if args[i]=="-q" || args[i]=="--quiet"
  quiet = true
  elseif args[i]=="--worker"
- start_worker()
- # doesn't return
+ worker_arg = (i == length(args)) ? "" : args[i+1]
+
+ if worker_arg == "custom"
+ i += 1
+ else
+ start_worker()
+ # doesn't return
+ end
+
  elseif args[i]=="--bind-to"
  i+=1 # has already been processed
  elseif args[i]=="-e" || args[i]=="--eval"

base/exports.jl

@@ -30,6 +30,7 @@ export
  BitArray,
  BitMatrix,
  BitVector,
+ BufferStream,
  CartesianIndex,
  CartesianRange,
  CFILE,
@@ -1218,6 +1219,7 @@ export
  nprocs,
  nworkers,
  pmap,
+ process_messages,
  procs,
  put!,
  remotecall,

base/multi.jl

@@ -303,7 +303,8 @@ function rmprocs(args...; waitfor = 0.0)
  else
  if haskey(map_pid_wrkr, i)
  push!(rmprocset, i)
- remote_do(i, exit)
+ w = map_pid_wrkr[i]
+ kill(w.manager, i, w.config)
  end
  end
  end
@@ -1286,6 +1287,12 @@ function connect(manager::ClusterManager, pid::Int, config::WorkerConfig)
  (s, s)
 end
 
+function kill(manager::ClusterManager, pid::Int, config::WorkerConfig)
+ remote_do(pid, exit) # For TCP based transports this will result in a close of the socket
+ # at our end, which will result in a cleanup of the worker.
+ nothing
+end
+
 function connect_w2w(pid::Int, config::WorkerConfig)
  (rhost, rport) = get(config.connect_at)
  config.host = rhost

base/stream.jl

@@ -960,3 +960,47 @@ mark(x::AsyncStream) = mark(x.buffer)
 unmark(x::AsyncStream) = unmark(x.buffer)
 reset(x::AsyncStream) = reset(x.buffer)
 ismarked(x::AsyncStream) = ismarked(x.buffer)
+
+# BufferStream's are non-OS streams, backed by a regular IOBuffer
+type BufferStream <: AsyncStream
+ buffer::IOBuffer
+ r_c::Condition
+ close_c::Condition
+ is_open::Bool
+
+ BufferStream() = new(PipeBuffer(), Condition(), Condition(), true)
+end
+
+isopen(s::BufferStream) = s.is_open
+close(s::BufferStream) = (s.is_open = false; notify(s.r_c; all=true); notify(s.close_c; all=true); nothing)
+
+function wait_readnb(s::BufferStream, nb::Int)
+ while isopen(s) && nb_available(s.buffer) < nb
+ wait(s.r_c)
+ end
+
+ (nb_available(s.buffer) < nb) && error("closed BufferStream")
+end
+
+function eof(s::BufferStream)
+ wait_readnb(s,1)
+ !isopen(s) && nb_available(s.buffer)<=0
+end
+
+show(io::IO, s::BufferStream) = print(io,"BufferStream() bytes waiting:",nb_available(s.buffer),", isopen:", s.is_open)
+
+nb_available(s::BufferStream) = nb_available(s.buffer)
+
+function wait_readbyte(s::BufferStream, c::UInt8)
+ while isopen(s) && search(s.buffer,c) <= 0
+ wait(s.r_c)
+ end
+end
+
+wait_close(s::BufferStream) = if isopen(s) wait(s.close_c); end
+start_reading(s::BufferStream) = nothing
+
+write(s::BufferStream, b::UInt8) = (rv=write(s.buffer, b); notify(s.r_c; all=true);rv)
+write{T}(s::BufferStream, a::Array{T}) = (rv=write(s.buffer, a); notify(s.r_c; all=true);rv)
+write(s::BufferStream, p::Ptr, nb::Integer) = (rv=write(s.buffer, p, nb); notify(s.r_c; all=true);rv)
+

doc/manual/parallel-computing.rst

@@ -674,21 +674,46 @@ retained.
 ClusterManagers
 ---------------
 
-Julia worker processes can also be spawned on arbitrary machines,
-enabling Julia's natural parallelism to function quite transparently
-in a cluster environment. The :class:`ClusterManager` interface provides a
-way to specify a means to launch and manage worker processes.
+The launching, management and networking of julia processes into a logical
+cluster is done via cluster managers. A ``ClusterManager`` is responsible for
 
-Thus, a custom cluster manager would need to:
+- launching worker processes in a cluster environment
+- managing events during the lifetime of each worker
+- optionally, a cluster manager can also provide data transport
 
-- be a subtype of the abstract :class:`ClusterManager`
-- implement :func:`launch`, a method responsible for launching new workers
-- implement :func:`manage`, which is called at various events during a worker's lifetime
+A julia cluster has the following characteristics:
+- The initial julia process, also called the ``master`` is special and has a julia id of 1.
+- Only the ``master`` process can add or remove worker processes.
+- All processes can directly communicate with each other.
+
+Connections between workers (using the in-built TCP/IP transport) is established in the following manner:
+- ``addprocs`` is called on the master process with a ``ClusterManager`` object
+- ``addprocs`` calls the appropriate ``launch`` method which spawns required
+ number of worker processes on appropriate machines
+- Each worker starts listening on a free port and writes out its host, port information to STDOUT
+- The cluster manager captures the stdout's of each worker and makes it available to the master process
+- The master process parses this information and sets up TCP/IP connections to each worker
+- Every worker is also notified of other workers in the cluster
+- Each worker connects to all workers whose julia id is less than its own id
+- In this way a mesh network is established, wherein every worker is directly connected with every other worker
+
+
+While the default transport layer uses plain TCP sockets, it is possible for a julia cluster to provide
+its own transport.
 
 Julia provides two in-built cluster managers:
 
-- :class:`LocalManager`, used when :func:`addprocs` or :func:`addprocs(::Integer) <addprocs>` are called
-- :class:`SSHManager`, used when :func:`addprocs(::Array) <addprocs>` is called with a list of hostnames
+- ``LocalManager``, used when :func:`addprocs` or :func:`addprocs(np::Integer) <addprocs>` are called
+- ``SSHManager``, used when :func:`addprocs(hostnames::Array) <addprocs>` is called with a list of hostnames
+
+:class:`LocalManager` is used to launch additional workers on the same host, thereby leveraging multi-core
+and multi-processor hardware.
+
+Thus, a minimal cluster manager would need to:
+
+- be a subtype of the abstract :class:`ClusterManager`
+- implement :func:`launch`, a method responsible for launching new workers
+- implement :func:`manage`, which is called at various events during a worker's lifetime
 
 :func:`addprocs(manager::FooManager) <addprocs>` requires ``FooManager`` to implement::
 
@@ -730,8 +755,8 @@ argument. Optionally ``--bind-to bind_addr[:port]`` may also be specified to ena
 to connect to it at the specified ``bind_addr`` and ``port``. Useful for multi-homed hosts.
 
 
-For every worker launched, the :func:`launch` method must add a :clas`WorkerConfig`
-object with appropriate fields initialized to ``launched`` ::
+For every worker launched, the :func:`launch` method must add a :class:`WorkerConfig`
+object (with appropriate fields initialized) to ``launched`` ::
 
  type WorkerConfig
  # Common fields relevant to all cluster managers
@@ -753,6 +778,8 @@ object with appropriate fields initialized to ``launched`` ::
  sshflags::Nullable{Cmd}
  max_parallel::Nullable{Integer}
 
+ connect_at::Nullable{Any}
+
  .....
  end
 
@@ -778,7 +805,6 @@ required to connect to the workers from the master process.
 ``userdata`` is provided for custom cluster managers to store their own worker specific information.
 
 
-
 :func:`manage(manager::FooManager, id::Integer, config::WorkerConfig, op::Symbol) <manage>` is called at different
 times during the worker's lifetime with different ``op`` values:
 
@@ -789,6 +815,59 @@ times during the worker's lifetime with different ``op`` values:
  interrupt signal.
  - with ``:finalize`` for cleanup purposes.
 
+
+Cluster Managers with custom transports
+---------------------------------------
+
+Replacing the default TCP/IP all-to-all socket connections with a custom transport layer is a little more involved.
+Each julia process has as many communication tasks as the workers it is connected to. For example, consider a julia cluster of
+32 processes in a all-to-all mesh network:
+
+ - Each julia process thus has 31 communication tasks
+ - Each task handles all incoming messages from a single remote worker in a message processing loop
+ - The message processing loop waits on an ``AsyncStream`` object - for example, a TCP socket in the default implementation, reads an entire
+ message, processes it and waits for the next one
+ - Sending messages to a process is done directly from any julia task - not just communication tasks - again, via the appropriate
+ ``AsyncStream`` object
+
+Replacing the default transport involves the new implementation to setup connections to remote workers, and to provide appropriate
+``AsyncStream`` objects that the message processing loops can wait on. The manager specific callbacks to be implemented are::
+
+ connect(manager::FooManager, pid::Integer, config::WorkerConfig)
+ kill(manager::FooManager, pid::Int, config::WorkerConfig)
+
+The default implementation (which uses TCP/IP sockets) is implemented as ``connect(manager::ClusterManager, pid::Integer, config::WorkerConfig)``.
+
+``connect`` should return a pair of ``AsyncStream`` objects, one for reading data sent from worker ``pid``,
+and the other to write data that needs to be sent to worker ``pid``. Custom cluster managers can use an in-memory ``BufferStream``
+as the plumbing to proxy data between the custom, possibly non-AsyncStream transport and julia's in-built parallel infrastructure.
+
+A ``BufferStream`` is an in-memory ``IOBuffer`` which behaves like an ``AsyncStream``.
+
+Folder ``examples/clustermanager/0mq`` is an example of using ZeroMQ is connect julia workers in a star network with a 0MQ broker in the middle.
+Note: The julia processes are still all *logically* connected to each other - any worker can message any other worker directly without any
+awareness of 0MQ being used as the transport layer.
+
+When using custom transports:
+ - julia workers must be started with arguments ``--worker custom``. Just ``--worker`` will result in the newly launched
+ workers defaulting to the socket transport implementation
+ - For every logical connection with a worker, :func:`process_messages(rd::AsyncStream, wr::AsyncStream)` must be called
+ This launches a new task that handles reading and writing of messages from/to the worker represented by the ``AsyncStream`` objects
+ - :func:`init_worker(manager::FooManager)` must be called as part of worker process initializaton
+ - Field ``connect_at::Any`` in :class:`WorkerConfig` can be set by the cluster manager when ``launch`` is called. The value of
+ this field is passed in in all ``connect`` callbacks. Typically, it carries information on *how to connect* to a worker. For example,
+ the TCP/IP socket transport uses this field to specify the ``(host, port)`` tuple at which to connect to a worker
+
+
+``kill(manager, pid, config)`` is called to remove a worker from the cluster.
+On the master process, the corresponding ``AsyncStream`` objects must be closed by the implementation to ensure proper cleanup. The default
+implementation simply executes an ``exit()`` call on the specified remote worker.
+
+``examples/clustermanager/simple`` is an example that shows a simple implementation using unix domain sockets for cluster setup
+
+
+
+
 .. rubric:: Footnotes
 
 .. [#mpi2rma] In this context, MPI refers to the MPI-1 standard. Beginning with MPI-2, the MPI standards committee introduced a new set of communication mechanisms, collectively referred to as Remote Memory Access (RMA). The motivation for adding RMA to the MPI standard was to facilitate one-sided communication patterns. For additional information on the latest MPI standard, see http:https://www.mpi-forum.org/docs.

doc/stdlib/parallel.rst

@@ -101,7 +101,7 @@ General Parallel Computing Support
 .. function:: addprocs(n::Integer; exeflags=``) -> List of process identifiers
 
  Launches workers using the in-built ``LocalManager`` which only launches workers on the local host.
- This can be used to take advantage of multiple cores. `addprocs(4)`` will add 4 processes on the local machine.
+ This can be used to take advantage of multiple cores. ``addprocs(4)`` will add 4 processes on the local machine.
 
 .. function:: addprocs() -> List of process identifiers
 

examples/clustermanager/0mq/README

@@ -0,0 +1,27 @@
+This is a proof-of-concept that uses ZeroMQ as transport.
+It uses a star topology as opposed to the native mesh network.
+
+Package ZMQ must be installed. All workers only run on localhost.
+
+All Julia nodes only connect to a "broker" process that listens on known ports
+8100 and 8101 via ZMQ sockets.
+
+
+All commands must be run from `examples/clustermanager/0mq` directory
+
+First, start the broker. In a new console type:
+ julia broker.jl
+
+This does not return.
+
+Next, start a Julia REPL and type:
+ include("ZMQCM.jl")
+ ZMQCM.start_master(4) # start with four workers
+
+
+Alternatively, head.jl, a test script could be run. It just launches the requested number of workers,
+executes a simple command on all of them and exits.
+ julia head.jl 4
+
+NOTE: As stated this is a proof-of-concept. A real Julia cluster using ZMQ will probably use
+different ZMQ socket types and optimize the transport.