API CHANGE: Static check for expressions

Traditionally the embedded expression language has been a source of wasted developer time because of its lazy and poor error reporting. In particular type checks were done at execution time an led to very late dynamic errors during execution time. Also missing bindings in <expression>-transitions were reported only at execution time when the transition fired.

The release 21.09 improves the situation and pnetc introduces static checks for a couple of situations:

  • Type errors in <expression>-transitions
  • Missing bindings in <expression>-transitions
  • Type errors in outputs of <expression>-transitions
  • Type errors in <size>- and <alignment>-expressions in <memory-buffer>s
  • Type errors in <local>- and <global>-expressions in memory transfer descriptions <memory-get> and <memory-put>
  • Type errors and missing bindings in the plugin commands gspc.we.plugin.create, gspc.we.plugin.call_before_eval, gspc.we.plugin.call_after_eval and gspc.we.plugin.destroy
  • Type errors in <eureka-group>-expressions
  • Type errors in scheduling data fhg.drts.schedule.num_worker and fhg.drts.schedule.dynamic_requirement

Existing applications continue to work without any change. With the exception of applications that contain type- or parse-errors in expression that are defined in dead code. Such application must remove the dead code.

EXAMPLE: Look at this code:

  <struct name="State">
    <field name="next" type="unsigned long"/>
    <transition name="step">
        <inout name="state" type="State"/>
        <out name="id" type="long"/>
          ${Id} := ${state.next};
          ${state.next} := ${state.next} - 1

This example code contains a number of errors (can you tell how many?) but pnetc in version 21.06 accepts it.

Compiling the example code with pnetc from version 21.09 on produces the error:

pnetc: failed: In 'anonymous' defined at [XPNET:1:1].
 In 'step' defined at [XPNET:7:7].
  In the <condition> expression '(
   type error: Expression '(
        )' has incompatible type 'unsigned long'. Expected type 'bool'.
    type error: At ${}: Can not assign a value of type 'unsigned long' to a value of type 'bool'

because the <condition> is not of type bool. After fixing it via

-          ${state.next}
+          ${state.next} :gt: 0UL

now pnetc produces another error:

pnetc: failed: In 'anonymous' defined at [XPNET:1:1].
 In 'step' defined at [XPNET:7:7].
  type error: In expression '${Id} := ${state.next};
          ${state.next} := ${state.next} - 1'
   type error: In '(${state.next} := (${state.next} - 1))'
    type error: The left argument '${state.next}' of ' - ' has type 'unsigned long' and the right argument '1' of ' - ' has type 'int' but the types should be the same

Oh, yes, thanks. The fix is easy:

-          ${state.next} := ${state.next} - 1
+          ${state.next} := ${state.next} - 1UL

Now pnetc produces the error:

pnetc: failed: In 'anonymous' defined at [XPNET:1:1].
 In 'step' defined at [XPNET:7:7].
  type error: In expression '${Id} := ${state.next};
          ${state.next} := ${state.next} - 1UL'
   missing binding for: ${id}

which points to a typo and is fixed by

-          ${Id} := ${state.next};
+          ${id} := ${state.next};

And yet there is another error detected by pnetc:

pnetc: failed: In 'anonymous' defined at [XPNET:1:1].
 In 'step' defined at [XPNET:7:7].
  type error: In expression '${id} := ${state.next};
          ${state.next} := ${state.next} - 1ul'
   Output port 'id' expects type 'long'
    type error: At ${id}: Can not assign a value of type 'unsigned long' to a value of type 'long'

which is fixed by either

-          ${id} := ${state.next};
+          ${id} := long (${state.next});

or by

-        <out name="id" type="long"/>
+        <out name="id" type="unsigned long"/>

API CHANGE: Standalone Util-Generic

GPISpace’s util-generic is now a standalone project with its own CMake package configuration file. A few more things to note:

  • util-generic is currently installed alongside GPISpace which is including it through its own CMake package configuration file. util-generic-config.cmake has the same root directory as GPISpace (i.e. util-generic_ROOT == GPISpace_ROOT)
  • A util-generic submodule can no longer exist in a GPISpace application. Keeping it will result in CMake errors.
  • In addition to the Util::Generic target, there is now also a Util::Generic-Headers target for the public headers.
  • Compilation now requires a C++14 capable compiler.
  • The following header files were removed and are no longer available:
    • cxx11/cxx03_compat.hpp
    • cxx14/enum_hash.hpp
    • cxx14/get_by_type.hpp
  • In GPISpace util-generic’s tests are disabled by default, to enable them UTIL_GENERIC_BUILD_TESTING needs to be set to ON.

API CHANGE: Fix: Allow recursive lists and sets in expressions

The types “list” and “set” in the expression language now allow for recursion. For example those expressions:

stack_push (List (1), List (""))
set_insert (Set {}, Set {})
set_erase (Set {Set {1}}, Set {1})
set_is_element (Set {Set {1}}, Set {""})

are now evaluating to the correct results

List (1, List (""))
Set {Set {}}
Set {}

In earlier versions of GPI-Space all those expressions led to evaluation errors.

API CHANGE: More specific error message when trying to retrieve nonexisting keys from maps in expressions

The attempt to retrieve a non-existing key from a map in an expression led to an exception ‘map::at’. Now a more informative error is produced. For example

map_get_assignment (Map[], 4) map_get_assignment (map_assign (Map[], “size”, 1), “Size”)

are now producing the evaluation errors

type error: eval map_get_assignment (Map [], 4)


type error: eval map_get_assignment (Map [“size” -> 1], “Size”)


API CHANGE: More precise error messages when jobs are unknown or not running

When a drts::client interacts with a workflow (e.g. to put a token or to get a response), then that workflow might be

  • unknown, for example if it was never submitted or has been forgotten already, or

  • not running, for example if it has been submitted but has not yet started or has already finished.

Errors now distinguish between the two cases, unlike before when the same error would show up for both cases.

API CHANGE: Save exception message from plugin constructors

Exception thrown by plugin constructors during workflow execution are created in the context of the dynamic library, which goes out of scope immediately and make the execution hang forever.

This commit changes the behavior such that the exception messages are saved while the dynamic library is still loaded. This approach forgets about the type of the exception, however, it allows the execution to continue and transports the exception message.

API CHANGE: Better transport failure reasons to users

Failure reasons during workflow executions (for example from Plugins) are better transported to users and the unspecified message “activity was terminated” has gone.

API CHANGE: Turn undefined behavior into exceptions when evaluating expressions

Some expressions led to undefined behavior, namely

stack_top (List()) stack_pop (List()) set_top (Set{}) set_pop (Set{})

were all doing invalid accesses into their internal storage.

All those cases now throw an we::expr::exception::eval.


  • Added a missing dependency entry for pkgconfig in the README.md and installation instructions.


  • In order to better meet the needs of our users, especially new users, we decided to overhaul our How-To-Use webpage (https://www.gpi-space.de/how-to-use).
  • Module call requirements are now always mandatory. Modules had been able to require capabilities with mandatory="false", which would prefer to execute on a worker having the capability but could run on any random worker otherwise.
    This feature has been superseded by preferences and specific implementations, which allows to specify the behavior with more detail.


  • The minimal version of cmake has been bumped to 3.15.