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| -rw-r--r-- | ml/dlib/examples/bsp_ex.cpp | 282 |
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diff --git a/ml/dlib/examples/bsp_ex.cpp b/ml/dlib/examples/bsp_ex.cpp new file mode 100644 index 000000000..7dffa68d6 --- /dev/null +++ b/ml/dlib/examples/bsp_ex.cpp @@ -0,0 +1,282 @@ +// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt +/* + + This is an example illustrating the use of the Bulk Synchronous Parallel (BSP) + processing tools from the dlib C++ Library. These tools allow you to easily setup a + number of processes running on different computers which cooperate to compute some + result. + + In this example, we will use the BSP tools to find the minimizer of a simple function. + In particular, we will setup a nested grid search where different parts of the grid are + searched in parallel by different processes. + + + To run this program you should do the following (supposing you want to use three BSP + nodes to do the grid search and, to make things easy, you will run them all on your + current computer): + + 1. Open three command windows and navigate each to the folder containing the + compiled bsp_ex.cpp program. Let's call these window 1, window 2, and window 3. + + 2. In window 1 execute this command: + ./bsp_ex -l12345 + This will start a listening BSP node that listens on port 12345. The BSP node + won't do anything until we tell all the nodes to start running in step 4 below. + + 3. In window 2 execute this command: + ./bsp_ex -l12346 + This starts another listening BSP node. Note that since we are running this + example all on one computer you need to use different listening port numbers + for each listening node. + + 4. In window 3 execute this command: + ./bsp_ex localhost:12345 localhost:12346 + This will start a BSP node that connects to the others and gets them all running. + Additionally, as you will see when we go over the code below, it will also print + the final output of the BSP process, which is the minimizer of our test function. + Once it terminates, all the other BSP nodes will also automatically terminate. +*/ + + + + + +#include <dlib/cmd_line_parser.h> +#include <dlib/bsp.h> +#include <dlib/matrix.h> + +#include <iostream> + +using namespace std; +using namespace dlib; + +// ---------------------------------------------------------------------------------------- + +// These are the functions executed by the BSP nodes. They are defined below. +void bsp_job_node_0 (bsp_context& bsp, double& min_value, double& optimal_x); +void bsp_job_other_nodes (bsp_context& bsp, long grid_resolution); + +// ---------------------------------------------------------------------------------------- + +int main(int argc, char** argv) +{ + try + { + // Use the dlib command_line_parser to parse the command line. See the + // compress_stream_ex.cpp example program for an introduction to the command line + // parser. + command_line_parser parser; + parser.add_option("h","Display this help message."); + parser.add_option("l","Run as a listening BSP node.",1); + parser.parse(argc, argv); + parser.check_option_arg_range("l", 1, 65535); + + + // Print a help message if the user gives -h on the command line. + if (parser.option("h")) + { + // display all the command line options + cout << "Usage: bsp_ex (-l port | <list of hosts>)\n"; + parser.print_options(); + return 0; + } + + + // If the command line contained -l + if (parser.option("l")) + { + // Get the argument to -l + const unsigned short listening_port = get_option(parser, "l", 0); + cout << "Listening on port " << listening_port << endl; + + const long grid_resolution = 100; + + // bsp_listen() starts a listening BSP job. This means that it will wait until + // someone calls bsp_connect() and connects to it before it starts running. + // However, once it starts it will call bsp_job_other_nodes() which will then + // do all the real work. + // + // The first argument is the port to listen on. The second argument is the + // function which it should run to do all the work. The other arguments are + // optional and allow you to pass values into the bsp_job_other_nodes() + // routine. In this case, we are passing the grid_resolution to + // bsp_job_other_nodes(). + bsp_listen(listening_port, bsp_job_other_nodes, grid_resolution); + } + else + { + if (parser.number_of_arguments() == 0) + { + cout << "You must give some listening BSP nodes as arguments to this program!" << endl; + return 0; + } + + // Take the hostname:port strings from the command line and put them into the + // vector of hosts. + std::vector<network_address> hosts; + for (unsigned long i = 0; i < parser.number_of_arguments(); ++i) + hosts.push_back(parser[i]); + + double min_value, optimal_x; + + // Calling bsp_connect() does two things. First, it tells all the BSP jobs + // listed in the hosts vector to start running. Second, it starts a locally + // running BSP job that executes bsp_job_node_0() and passes it any arguments + // listed after bsp_job_node_0. So in this case it passes it the 3rd and 4th + // arguments. + // + // Note also that we use dlib::ref() which causes these arguments to be passed + // by reference. This means that bsp_job_node_0() will be able to modify them + // and we will see the results here in main() after bsp_connect() terminates. + bsp_connect(hosts, bsp_job_node_0, dlib::ref(min_value), dlib::ref(optimal_x)); + + // bsp_connect() and bsp_listen() block until all the BSP nodes have terminated. + // Therefore, we won't get to this part of the code until the BSP processing + // has finished. But once we do we can print the results like so: + cout << "optimal_x: "<< optimal_x << endl; + cout << "min_value: "<< min_value << endl; + } + + } + catch (std::exception& e) + { + cout << "error in main(): " << e.what() << endl; + } +} + +// ---------------------------------------------------------------------------------------- + +/* + We are going to use the BSP tools to find the minimum of f(x). Note that + it's minimizer is at x == 2.0. +*/ +double f (double x) +{ + return std::pow(x-2.0, 2.0); +} + +// ---------------------------------------------------------------------------------------- + +void bsp_job_node_0 (bsp_context& bsp, double& min_value, double& optimal_x) +{ + // This function is called by bsp_connect(). In general, any BSP node can do anything + // you want. However, in this example we use this node as a kind of controller for the + // other nodes. In particular, since we are doing a nested grid search, this node's + // job will be to collect results from other nodes and then decide which part of the + // number line subsequent iterations should focus on. + // + // Also, each BSP node has a node ID number. You can determine it by calling + // bsp.node_id(). However, the node spawned by a call to bsp_connect() always has a + // node ID of 0 (hence the name of this function). Additionally, all functions + // executing a BSP task always take a bsp_context as their first argument. This object + // is the interface that allows BSP jobs to communicate with each other. + + + // Now let's get down to work. Recall that we are trying to find the x value that + // minimizes the f(x) defined above. The grid search will start out by considering the + // range [-1e100, 1e100] on the number line. It will progressively narrow this window + // until it has located the minimizer of f(x) to within 1e-15 of its true value. + double left = -1e100; + double right = 1e100; + + min_value = std::numeric_limits<double>::infinity(); + double interval_width = std::abs(right-left); + + // keep going until the window is smaller than 1e-15. + while (right-left > 1e-15) + { + // At the start of each loop, we broadcast the current window to all the other BSP + // nodes. They will each search a separate part of the window and then report back + // the smallest values they found in their respective sub-windows. + // + // Also, you can send/broadcast/receive anything that has global serialize() and + // deserialize() routines defined for it. Dlib comes with serialization functions + // for a lot of types by default, so we don't have to define anything for this + // example program. However, if you want to send an object you defined then you + // will need to write your own serialization functions. See the documentation for + // dlib's serialize() routine or the bridge_ex.cpp example program for an example. + bsp.broadcast(left); + bsp.broadcast(right); + + // Receive the smallest values found from the other BSP nodes. + for (unsigned int k = 1; k < bsp.number_of_nodes(); ++k) + { + // The other nodes will send std::pairs of x/f(x) values. So that is what we + // receive. + std::pair<double,double> val; + bsp.receive(val); + // save the smallest result. + if (val.second < min_value) + { + min_value = val.second; + optimal_x = val.first; + } + } + + // Now narrow the search window by half. + interval_width *= 0.5; + left = optimal_x - interval_width/2; + right = optimal_x + interval_width/2; + } +} + +// ---------------------------------------------------------------------------------------- + +void bsp_job_other_nodes (bsp_context& bsp, long grid_resolution) +{ + // This is the BSP job called by bsp_listen(). In these jobs we will receive window + // ranges from the controller node, search our sub-window, and then report back the + // location of the best x value we found. + + double left, right; + + // The try_receive() function will either return true with the next message or return + // false if there aren't any more messages in flight between nodes and all other BSP + // nodes are blocked on calls to receive or have terminated. That is, try_receive() + // only returns false if waiting for a message would result in all the BSP nodes + // waiting forever. + // + // Therefore, try_receive() serves both as a message receiving tool as well as an + // implicit form of barrier synchronization. In this case, we use it to know when to + // terminate. That is, we know it is time to terminate if all the messages between + // nodes have been received and all nodes are inactive due to either termination or + // being blocked on a receive call. This will happen once the controller node above + // terminates since it will result in all the other nodes inevitably becoming blocked + // on this try_receive() line with no messages to process. + while (bsp.try_receive(left)) + { + bsp.receive(right); + + // Compute a sub-window range for us to search. We use our node's ID value and the + // total number of nodes to select a subset of the [left, right] window. We will + // store the grid points from our sub-window in values_to_check. + const double l = (bsp.node_id()-1)/(bsp.number_of_nodes()-1.0); + const double r = bsp.node_id() /(bsp.number_of_nodes()-1.0); + const double width = right-left; + // Select grid_resolution number of points which are linearly spaced throughout our + // sub-window. + const matrix<double> values_to_check = linspace(left+l*width, left+r*width, grid_resolution); + + // Search all the points in values_to_check and figure out which one gives the + // minimum value of f(). + double best_x = 0; + double best_val = std::numeric_limits<double>::infinity(); + for (long j = 0; j < values_to_check.size(); ++j) + { + double temp = f(values_to_check(j)); + if (temp < best_val) + { + best_val = temp; + best_x = values_to_check(j); + } + } + + // Report back the identity of the best point we found in our sub-window. Note + // that the second argument to send(), the 0, is the node ID to send to. In this + // case we send our results back to the controller node. + bsp.send(make_pair(best_x, best_val), 0); + } +} + +// ---------------------------------------------------------------------------------------- + |