Add a script to be ran on snapshot dump

doc/RTD/source/ParameterFiles/parameter_description.rst

@@ -774,6 +774,19 @@ the SHUFFLE filter is also applied to get higher compression rates. Note that up
 until HDF5 1.10.x this option is not available when using the MPI-parallel
 version of the i/o routines.
 
+Users can run a program after a snapshot is dumped to disk using the following
+parameters:
+
+* Use the extra command after snapshot creation: ``run_on_dump`` (default :``0``)
+* Command to run after snapshot creation: ``dump_command`` (default: nothing)
+
+These are particularly useful should you wish to submit a job for postprocessing
+the snapshot after it has just been created. Your script will be invoked with
+two parameters, the snapshot base-name, and the snapshot number that was just
+output as a zero-padded integer. For example, if the base-name is "eagle" and
+snapshot 7 was just dumped, with ``dump_command`` set to ``./postprocess.sh``,
+then SWIFT will run ``./postprocess.sh eagle 0007``.
+
 Finally, it is possible to specify a different system of units for the snapshots
 than the one that was used internally by SWIFT. The format is identical to the
 one described above (See the :ref:`Parameters_units` section) and read:

examples/parameter_example.yml

@@ -156,6 +156,9 @@ Snapshots:
   output_list:         snaplist.txt # (Optional) File containing the output times (see documentation in "Parameter File" section)
   select_output_on:    0  # (Optional) Enable the output selection behaviour
   select_output:       selectoutput.yml # (Optional) File containing information to select outputs with (see documentation in the "Output Selection" section)
+  run_on_dump:         0 # (Optional) Run the dump_command each time that a snapshot is dumped?
+  dump_command:        ./submit_velociraptor.sh # (Optional) Command to run each time that a snapshot is dumped.
+  
 
 # Parameters governing the logger snapshot system
 Logger:

src/engine.c

@@ -2711,6 +2711,12 @@ void engine_init(struct engine *e, struct space *s, struct swift_params *params,
   parser_get_param_string(params, "Snapshots:basename", e->snapshot_base_name);
   parser_get_opt_param_string(params, "Snapshots:subdir", e->snapshot_subdir,
                               engine_default_snapshot_subdir);
+  e->snapshot_run_on_dump =
+      parser_get_opt_param_int(params, "Snapshots:run_on_dump", 0);
+  if (e->snapshot_run_on_dump) {
+    parser_get_param_string(params, "Snapshots:dump_command",
+                            e->snapshot_dump_command);
+  }
   e->snapshot_compression =
       parser_get_opt_param_int(params, "Snapshots:compression", 0);
   e->snapshot_distributed =

src/engine.h

@@ -311,6 +311,8 @@ struct engine {
 
   char snapshot_base_name[PARSER_MAX_LINE_SIZE];
   char snapshot_subdir[PARSER_MAX_LINE_SIZE];
+  char snapshot_dump_command[PARSER_MAX_LINE_SIZE];
+  int snapshot_run_on_dump;
   int snapshot_distributed;
   int snapshot_compression;
   int snapshot_int_time_label_on;
@@ -565,6 +567,7 @@ void engine_check_for_dumps(struct engine *e);
 void engine_check_for_index_dump(struct engine *e);
 void engine_collect_end_of_step(struct engine *e, int apply);
 void engine_dump_snapshot(struct engine *e);
+void engine_run_on_dump(struct engine *e);
 void engine_init_output_lists(struct engine *e, struct swift_params *params);
 void engine_init(struct engine *e, struct space *s, struct swift_params *params,
                  struct output_options *output_options, long long Ngas,

src/engine_io.c

@@ -39,6 +39,8 @@
 #include "serial_io.h"
 #include "single_io.h"
 
+#include <stdio.h>
+
 /**
  * @brief Check whether an index file has to be written during this
  * step.
@@ -214,6 +216,34 @@ void engine_dump_snapshot(struct engine *e) {
   if (e->verbose)
     message("writing particle properties took %.3f %s.",
             (float)clocks_diff(&time1, &time2), clocks_getunit());
+
+  /* Run the post-dump command if required */
+  engine_run_on_dump(e);
+}
+
+/**
+ * @brief Runs the snapshot_dump_command if relevant. Note that we
+ *        perform no error checking on this command, and assume
+ *        it works fine.
+ *
+ * @param e The #engine.
+ */
+void engine_run_on_dump(struct engine *e) {
+  if (e->snapshot_run_on_dump) {
+    /* Generate a string containing (optionally) the snapshot number.
+     * Note that -1 is used because snapshot_output_count was just
+     * increased when the write_output_* functions are called. */
+    const int buf_size = PARSER_MAX_LINE_SIZE * 3;
+    char dump_command_buf[buf_size];
+    snprintf(dump_command_buf, buf_size, "%s %s %04d", e->snapshot_dump_command,
+             e->snapshot_base_name, e->snapshot_output_count - 1);
+
+    /* Let's trust the user's command... */
+    const int result = system(dump_command_buf);
+    if (result != 0) {
+      message("Snapshot dump command returned error code %d", result);
+    }
+  }
 }
 
 /**

src/restart.c

@@ -358,5 +358,7 @@ void restart_resubmit(const char *command) {
 
   /* Let's trust the user's command... */
   const int result = system(command);
-  if (result != 0) message("Command returned error code %d", result);
+  if (result != 0) {
+    message("Restart resubmit command returned error code %d", result);
+  }
 }