From 9f47299db09f1dd29fbe629f85d0de2876567612 Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Thu, 28 May 2026 15:15:31 +0200
Subject: [PATCH 1/5] Fix spike recording bug.

---
 VERSION                                      |  2 +-
 arbor/simulation.cpp                         |  7 ++++++-
 doc/concepts/decor.rst                       |  2 +-
 doc/python/interconnectivity.rst             |  2 +-
 doc/python/simulation.rst                    |  4 ++++
 python/example/network_ring_mpi.py           |  6 +++---
 python/example/single_cell_bluepyopt_l5pc.py | 16 +++++++++-------
 7 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/VERSION b/VERSION
index 26acbf080b..aa22d3ce39 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.12.2
+0.12.3
diff --git a/arbor/simulation.cpp b/arbor/simulation.cpp
index 2297860529..c7a63994d8 100644
--- a/arbor/simulation.cpp
+++ b/arbor/simulation.cpp
@@ -434,7 +434,12 @@ time_type simulation_state::run(time_type tfinal, time_type dt) {
         // Present spikes to user-supplied callbacks.
         PE(spikeio);
         if (local_export_callback_) local_export_callback_(all_local_spikes);
-        if (global_export_callback_) global_export_callback_(spikes.from_local.values());
+        // If we are asked to export all spikes, clench your teeth and collate all spikes.
+        // TODO(TH): probably need to deprecate this, then. 
+        if (global_export_callback_) {
+            auto global_spikes = ctx_->distributed->gather_spikes(all_local_spikes);
+            global_export_callback_(global_spikes.values());
+        }
         PL(spikeio);
 
         // Append events formed from global spikes to per-cell pending event queues.
diff --git a/doc/concepts/decor.rst b/doc/concepts/decor.rst
index 36e8379015..92528753e7 100644
--- a/doc/concepts/decor.rst
+++ b/doc/concepts/decor.rst
@@ -382,7 +382,7 @@ between cells. An example where we're interested in when a threshold of ``-10 mV
 
     # Placing a threshold detector might look like this.
     decor = arbor.decor()
-    decor.place('"root"', arbor.threshold_detector(-10), "detector")
+    decor.place('"root"', arbor.threshold_detector(-10*U.mV), "detector")
 
     # At this point, "detector" could be connected to another cell,
     # and it would transmit events upon the voltage crossing the threshold.
diff --git a/doc/python/interconnectivity.rst b/doc/python/interconnectivity.rst
index 97202694fb..9733cb8042 100644
--- a/doc/python/interconnectivity.rst
+++ b/doc/python/interconnectivity.rst
@@ -58,7 +58,7 @@ Interconnectivity
             # Place 'expsyn' mechanism on "synapse_site", and a threshold detector at "root"
             decor = A.decor()
             decor.place('"synapse_site"', 'expsyn', 'syn')
-            decor.place('"root"', arbor.threshold_detector(-10), 'detector')
+            decor.place('"root"', arbor.threshold_detector(-10*U.mV), 'detector')
 
             # Implement the connections_on() function on a recipe as follows:
             def connections_on(gid):
diff --git a/doc/python/simulation.rst b/doc/python/simulation.rst
index 09b497509b..6614ae47ed 100644
--- a/doc/python/simulation.rst
+++ b/doc/python/simulation.rst
@@ -200,6 +200,10 @@ over the local and distributed hardware resources (see :ref:`pydomdec`). Then, t
 
         Record all generated spikes from cells on all MPI ranks.
 
+        **Note** This convenience method has non-trivial performance
+         implications as Arbor will collate all spikes on all ranks. Prefer
+         ``local`` unless you are absolutely required otherwise and willing to
+         pay the cost.
 
 Recording spikes
 ----------------
diff --git a/python/example/network_ring_mpi.py b/python/example/network_ring_mpi.py
index 2a30010844..7858799d22 100644
--- a/python/example/network_ring_mpi.py
+++ b/python/example/network_ring_mpi.py
@@ -68,7 +68,7 @@ def make_cable_cell(gid):
         # (4) Attach a single synapse.
         .place('"synapse_site"', A.synapse("expsyn"), "syn")
         # Attach a detector with threshold of -10 mV.
-        .place('"root"', A.threshold_detector(-10), "detector")
+        .place('"root"', A.threshold_detector(-10 * U.mV), "detector")
     )
 
     return A.cable_cell(tree, decor, labels)
@@ -114,7 +114,7 @@ def event_generators(self, gid):
 
     # (10) Place a probe at the root of each cell.
     def probes(self, gid):
-        return [A.cable_probe_membrane_voltage('"root"')]
+        return [A.cable_probe_membrane_voltage('"root"', tag='Um')]
 
     def global_properties(self, kind):
         return self.props
@@ -139,7 +139,7 @@ def global_properties(self, kind):
 
 # (15) Attach a sampler to the voltage probe on cell 0. Sample rate of 1 sample every ms.
 # Sampling period increased w.r.t network_ring.py to reduce amount of data
-handles = [sim.sample((gid, 0), A.regular_schedule(1 * U.ms)) for gid in range(ncells)]
+handles = [sim.sample((gid, 'Um'), A.regular_schedule(1 * U.ms)) for gid in range(ncells)]
 
 # (16) Run simulation
 sim.run(ncells * 5 * U.ms)
diff --git a/python/example/single_cell_bluepyopt_l5pc.py b/python/example/single_cell_bluepyopt_l5pc.py
index 42a08ed6f8..b6143c38a2 100755
--- a/python/example/single_cell_bluepyopt_l5pc.py
+++ b/python/example/single_cell_bluepyopt_l5pc.py
@@ -1,6 +1,8 @@
 #!/usr/bin/env python3
 
 import arbor as A
+from arbor import units as U
+
 import pandas
 import seaborn
 import sys
@@ -27,19 +29,19 @@
 )
 
 # (3) Define stimulus and spike detector, adjust discretization
-decor.place('"soma_center"', A.i_clamp(tstart=295, duration=5, current=1.9))
+decor.place('"soma_center"', A.i_clamp(tstart=295*U.ms, duration=5*U.ms, current=1.9*U.nA))
 
 # Add spike detector
-decor.place('"soma_center"', A.threshold_detector(-10), "detector")
+decor.place('"soma_center"', A.threshold_detector(-10*U.mV), "detector")
 
 # Adjust discretization (single CV on soma, default everywhere else)
-cvp = A.cv_policy_max_extent_um(1.0) | A.cv_policy_single('"soma"')
+cvp = A.cv_policy_max_extent_um(1.0*U.um) | A.cv_policy_single('"soma"')
 
 # (4) Create the cell.
 cell = A.cable_cell(morpho, decor, labels, cvp)
 
 # (5) Declare a probe.
-probe = A.cable_probe_membrane_voltage('"dend1"')
+probe = A.cable_probe_membrane_voltage('"dend1"', tag='Um')
 
 
 # (6) Create a class that inherits from A.recipe
@@ -90,11 +92,11 @@ def global_properties(self, gid):
 # Instruct the simulation to record the spikes and sample the probe
 sim.record(A.spike_recording.all)
 
-probe_id = A.cell_member(0, 0)
-handle = sim.sample(probe_id, A.regular_schedule(0.02))
+probe_id = A.cell_member(0, 'Um')
+handle = sim.sample(probe_id, A.regular_schedule(0.02*U.ms))
 
 # (8) Run the simulation
-sim.run(tfinal=600, dt=0.025)
+sim.run(tfinal=600*U.ms, dt=0.025*U.ms)
 
 # (9) Print or display the results
 spikes = sim.spikes()

From 93e46876ac911aa43e5463f6e816c3333c671ba2 Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Fri, 29 May 2026 07:59:44 +0200
Subject: [PATCH 2/5] Breaking: remove global spike callback.

---
 VERSION                   | 2 +-
 doc/cpp/simulation.rst    | 5 +++++
 example/busyring/ring.cpp | 6 ++++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/VERSION b/VERSION
index aa22d3ce39..554c968455 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.12.3
+0.12.3rc0
diff --git a/doc/cpp/simulation.rst b/doc/cpp/simulation.rst
index 78fe0ada49..d0a7359e79 100644
--- a/doc/cpp/simulation.rst
+++ b/doc/cpp/simulation.rst
@@ -89,6 +89,11 @@ Class documentation
         during a simulation. See :cpp:func:`set_local_spike_callback` and
         :cpp:func:`set_global_spike_callback`.
 
+        **Note** This convenience method has non-trivial performance
+        implications as Arbor will collate all spikes on all ranks. Prefer
+        ``local`` unless you are absolutely required otherwise and willing to
+        pay the cost.
+
     **Constructor:**
 
     .. cpp:function:: simulation(const recipe& rec, const domain_decomposition& decomp, const context& ctx, std::uint64_t seed)
diff --git a/example/busyring/ring.cpp b/example/busyring/ring.cpp
index 1718dc5eb5..5688e008d9 100644
--- a/example/busyring/ring.cpp
+++ b/example/busyring/ring.cpp
@@ -342,7 +342,9 @@ int main(int argc, char** argv) {
         // Write spikes to file
         if (root) {
             std::cout << "\n" << ns << " spikes generated at rate of "
-                      << params.duration/ns << " ms between spikes\n";
+                      << params.duration/ns << " ms between spikes\n"
+                      << recorded_spikes.size() << " where recorded\n"
+;
             if (!recorded_spikes.empty()) {
                 std::ofstream fid(params.odir + "/" + params.name + "_spikes.gdf");
                 if (!fid.good()) {
@@ -541,4 +543,4 @@ arb::cable_cell branch_cell(arb::cell_gid_type gid, const cell_parameters& param
 
     // Make a CV between every sample in the sample tree.
     return {arb::morphology(tree), decor, {}, arb::cv_policy_every_segment()};
-}
\ No newline at end of file
+}

From 9e9b8b2b0c35a5d6bdfade21ed6f5fd909c02bce Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Fri, 29 May 2026 08:53:09 +0200
Subject: [PATCH 3/5] Update docs and examples

---
 VERSION                                       |  2 +-
 arbor/include/arbor/simulation.hpp            |  4 +-
 arbor/simulation.cpp                          |  9 +---
 doc/cpp/simulation.rst                        | 22 ++--------
 example/adex/adex.cpp                         |  2 +-
 example/brunel/brunel.cpp                     | 17 ++++----
 example/busyring/ring.cpp                     | 42 +++++++++----------
 example/dryrun/dryrun.cpp                     | 40 ++++++++----------
 example/gap_junctions/gap_junctions.cpp       | 40 ++++++++----------
 .../network_description.cpp                   | 38 +++++++----------
 example/plasticity/plasticity.cpp             |  2 +-
 example/ring/ring.cpp                         |  9 ++--
 python/simulation.cpp                         |  6 ---
 test/unit/test_adex_cell_group.cpp            | 14 +++----
 test/unit/test_lif_cell_group.cpp             |  4 +-
 test/unit/test_simulation.cpp                 |  4 +-
 test/unit/test_spikes.cpp                     |  2 +-
 17 files changed, 103 insertions(+), 154 deletions(-)

diff --git a/VERSION b/VERSION
index 554c968455..420b4fc259 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.12.3rc0
+0.12.3-rc0
diff --git a/arbor/include/arbor/simulation.hpp b/arbor/include/arbor/simulation.hpp
index 824a2e731c..6ce8754a89 100644
--- a/arbor/include/arbor/simulation.hpp
+++ b/arbor/include/arbor/simulation.hpp
@@ -74,8 +74,8 @@ struct ARB_ARBOR_API simulation {
 
     std::size_t num_spikes() const;
 
-    // Register a callback that will perform a export of the global
-    // spike vector.
+    // Register a callback that will perform a export of the global spike
+    // vector. REMOVED
     void set_global_spike_callback(spike_export_function = spike_export_function{});
 
     // Register a callback that will perform a export of the rank local
diff --git a/arbor/simulation.cpp b/arbor/simulation.cpp
index c7a63994d8..363cfb763b 100644
--- a/arbor/simulation.cpp
+++ b/arbor/simulation.cpp
@@ -100,7 +100,6 @@ struct simulation_state {
         return tau;
     }
 
-    spike_export_function global_export_callback_;
     spike_export_function local_export_callback_;
     epoch_function epoch_callback_;
     label_resolution_map source_resolution_map_;
@@ -434,12 +433,6 @@ time_type simulation_state::run(time_type tfinal, time_type dt) {
         // Present spikes to user-supplied callbacks.
         PE(spikeio);
         if (local_export_callback_) local_export_callback_(all_local_spikes);
-        // If we are asked to export all spikes, clench your teeth and collate all spikes.
-        // TODO(TH): probably need to deprecate this, then. 
-        if (global_export_callback_) {
-            auto global_spikes = ctx_->distributed->gather_spikes(all_local_spikes);
-            global_export_callback_(global_spikes.values());
-        }
         PL(spikeio);
 
         // Append events formed from global spikes to per-cell pending event queues.
@@ -625,7 +618,7 @@ std::size_t simulation::num_spikes() const {
 }
 
 void simulation::set_global_spike_callback(spike_export_function export_callback) {
-    impl_->global_export_callback_ = std::move(export_callback);
+    throw std::runtime_error("Attempted to call deprecated method: set_global_spike_callback");
 }
 
 void simulation::set_local_spike_callback(spike_export_function export_callback) {
diff --git a/doc/cpp/simulation.rst b/doc/cpp/simulation.rst
index d0a7359e79..bf87918ab4 100644
--- a/doc/cpp/simulation.rst
+++ b/doc/cpp/simulation.rst
@@ -86,13 +86,7 @@ Class documentation
     .. cpp:type:: spike_export_function = std::function<void(const std::vector<spike>&)>
 
         User-supplied callback function used as a sink for spikes generated
-        during a simulation. See :cpp:func:`set_local_spike_callback` and
-        :cpp:func:`set_global_spike_callback`.
-
-        **Note** This convenience method has non-trivial performance
-        implications as Arbor will collate all spikes on all ranks. Prefer
-        ``local`` unless you are absolutely required otherwise and willing to
-        pay the cost.
+        during a simulation. See :cpp:func:`set_local_spike_callback`.
 
     **Constructor:**
 
@@ -118,10 +112,9 @@ Class documentation
 
     **I/O:**
 
-    .. cpp:function:: sampler_association_handle add_sampler(\
-                        cell_member_predicate probeset_ids,\
-                        schedule sched,\
-                        sampler_function f)
+    .. cpp:function:: sampler_association_handle add_sampler(cell_member_predicate probeset_ids,\
+                                                             schedule sched,\
+                                                             sampler_function f)
 
         Note: sampler functions may be invoked from a different thread than that
         which is called :cpp:func:`run`.
@@ -150,13 +143,6 @@ Class documentation
         The total number of spikes generated since either construction or
         the last call to :cpp:func:`reset`.
 
-    .. cpp:function:: void set_global_spike_callback(spike_export_function export_callback)
-
-        Register a callback that will periodically be passed a vector with all of
-        the spikes generated over all domains (the global spike vector) since
-        the last call.
-        Will be called on the MPI rank/domain with id 0.
-
     .. cpp:function:: void set_local_spike_callback(spike_export_function export_callback)
 
         Register a callback that will periodically be passed a vector with all of
diff --git a/example/adex/adex.cpp b/example/adex/adex.cpp
index cc02d699e2..96dc4afc75 100644
--- a/example/adex/adex.cpp
+++ b/example/adex/adex.cpp
@@ -96,7 +96,7 @@ int main(int argc, char** argv) {
     sim.add_sampler(arb::all_probes,
                     arb::regular_schedule(opt.dt * U::ms),
                     sampler);
-    sim.set_global_spike_callback([](const auto& spks) {
+    sim.set_local_spike_callback([](const auto& spks) {
         for (const auto& spk: spks) {
             std::cerr << spk.time << ", " << spk.source.gid << ", " << spk.source.index << '\n';
         }
diff --git a/example/brunel/brunel.cpp b/example/brunel/brunel.cpp
index 5ea90607e2..c40657a26b 100644
--- a/example/brunel/brunel.cpp
+++ b/example/brunel/brunel.cpp
@@ -244,15 +244,16 @@ struct brunel_recipe: public recipe {
 };
 
 int main(int argc, char** argv) {
-    bool root = true;
-
     try {
+        bool root = true;
+        int rank = 0;
 #ifdef ARB_MPI_ENABLED
         arbenv::with_mpi guard(argc, argv, false);
         unsigned num_threads = arbenv::default_concurrency();
         int gpu_id = arbenv::find_private_gpu(MPI_COMM_WORLD);
         auto context = arb::make_context(arb::proc_allocation{num_threads, gpu_id}, MPI_COMM_WORLD);
-        root = arb::rank(context) == 0;
+        rank = arb::rank(context);
+        root = rank == 0;
 #else
         auto context = arb::make_context(arbenv::default_allocation());
 #endif
@@ -277,8 +278,8 @@ int main(int argc, char** argv) {
 
         std::fstream spike_out;
         auto spike_file_output = options.spike_file_output;
-        if (spike_file_output != "" && root) {
-            spike_out = sup::open_or_throw(spike_file_output, std::ios_base::out, false);
+        if (spike_file_output != "") {
+            spike_out = sup::open_or_throw(spike_file_output + "-" + std::to_string(rank) + ".gdf", std::ios_base::out, false);
         }
 
         meters.checkpoint("setup", context);
@@ -326,9 +327,9 @@ int main(int argc, char** argv) {
         // Set up spike recording.
         std::vector<arb::spike> recorded_spikes;
         if (spike_out) {
-            sim.set_global_spike_callback([&recorded_spikes](auto& spikes) {
-                    recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                });
+            sim.set_local_spike_callback([&recorded_spikes](auto& spikes) {
+                recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+            });
         }
 
         meters.checkpoint("model-init", context);
diff --git a/example/busyring/ring.cpp b/example/busyring/ring.cpp
index 5688e008d9..5120014689 100644
--- a/example/busyring/ring.cpp
+++ b/example/busyring/ring.cpp
@@ -247,6 +247,7 @@ std::string get_arbor_config_str() {
 }
 
 int main(int argc, char** argv) {
+    int rank = 0;
     try {
         bool root = true;
 
@@ -260,7 +261,7 @@ int main(int argc, char** argv) {
         arbenv::with_mpi guard(argc, argv, false);
         resources.gpu_id = arbenv::find_private_gpu(MPI_COMM_WORLD);
         auto context = arb::make_context(resources, MPI_COMM_WORLD);
-        auto rank = arb::rank(context);
+        rank = arb::rank(context);
         root = rank == 0;
 #else
         resources.gpu_id = arbenv::default_gpu();
@@ -321,11 +322,10 @@ int main(int argc, char** argv) {
 
         // Set up recording of spikes to a vector on the root process.
         std::vector<arb::spike> recorded_spikes;
-        if (root && params.record_spikes) {
-            sim.set_global_spike_callback(
-                [&recorded_spikes](const std::vector<arb::spike>& spikes) {
-                    recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                });
+        if (params.record_spikes) {
+            sim.set_local_spike_callback([&recorded_spikes](const std::vector<arb::spike>& spikes) {
+                recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+            });
         }
 
         meters.checkpoint("model-init", context);
@@ -341,23 +341,19 @@ int main(int argc, char** argv) {
 
         // Write spikes to file
         if (root) {
-            std::cout << "\n" << ns << " spikes generated at rate of "
-                      << params.duration/ns << " ms between spikes\n"
-                      << recorded_spikes.size() << " where recorded\n"
-;
-            if (!recorded_spikes.empty()) {
-                std::ofstream fid(params.odir + "/" + params.name + "_spikes.gdf");
-                if (!fid.good()) {
-                    std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
-                }
-                else {
-                    char linebuf[45];
-                    for (auto spike: recorded_spikes) {
-                        auto n = std::snprintf(
-                            linebuf, sizeof(linebuf), "%u %.4f\n",
-                            unsigned{spike.source.gid}, float(spike.time));
-                        fid.write(linebuf, n);
-                    }
+            std::cout << "\n" << ns << " spikes generated at rate of " << params.duration/ns << " ms between spikes\n";
+        }
+        if (!recorded_spikes.empty()) {
+            std::ofstream fid(params.odir + "/" + params.name + "-" + std::to_string(rank) + "_spikes.gdf");
+            if (!fid.good()) {
+                std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
+            }
+            else {
+                char linebuf[45];
+                for (auto spike: recorded_spikes) {
+                    auto n = std::snprintf(linebuf, sizeof(linebuf),
+                                           "%u %.4f\n", unsigned{spike.source.gid}, float(spike.time));
+                    fid.write(linebuf, n);
                 }
             }
         }
diff --git a/example/dryrun/dryrun.cpp b/example/dryrun/dryrun.cpp
index b49b651f07..974c008528 100644
--- a/example/dryrun/dryrun.cpp
+++ b/example/dryrun/dryrun.cpp
@@ -125,6 +125,7 @@ class tile_desc: public arb::tile {
 };
 
 int main(int argc, char** argv) {
+    int rank = 0;
     try {
 #ifdef ARB_MPI_ENABLED
         arbenv::with_mpi guard(argc, argv, false);
@@ -142,7 +143,8 @@ int main(int argc, char** argv) {
         else {
             ctx = arb::make_context(resources, MPI_COMM_WORLD);
             if (params.defaulted) params.num_ranks = arb::num_ranks(ctx);
-            root = arb::rank(ctx)==0;
+            rank = arb::rank(ctx);        
+            root = rank == 0;
         }
 #endif
 
@@ -182,12 +184,9 @@ int main(int argc, char** argv) {
 
         // Set up recording of spikes to a vector on the root process.
         std::vector<arb::spike> recorded_spikes;
-        if (root) {
-            sim.set_global_spike_callback(
-                    [&recorded_spikes](const std::vector<arb::spike>& spikes) {
-                        recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                    });
-        }
+        sim.set_local_spike_callback([&recorded_spikes](const std::vector<arb::spike>& spikes) {
+            recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+        });
 
         meters.checkpoint("model-init", ctx);
 
@@ -201,23 +200,20 @@ int main(int argc, char** argv) {
                   << params.duration/ns << " ms between spikes\n\n";
 
         // Write spikes to file
-        if (root) {
-            std::ofstream fid("spikes.gdf");
-            if (!fid.good()) {
-                std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
-            }
-            else {
-                char linebuf[45];
-                for (auto spike: recorded_spikes) {
-                    auto n = std::snprintf(
-                            linebuf, sizeof(linebuf), "%u %.4f\n",
-                            unsigned{spike.source.gid}, float(spike.time));
-                    fid.write(linebuf, n);
-                }
+        std::ofstream fid("spikes" + std::to_string(rank) + ".gdf");
+        if (!fid.good()) {
+            std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
+        }
+        else {
+            char linebuf[45];
+            for (auto spike: recorded_spikes) {
+                auto n = std::snprintf(linebuf, sizeof(linebuf),
+                                       "%u %.4f\n", unsigned{spike.source.gid}, float(spike.time));
+                fid.write(linebuf, n);
             }
-            // Write the samples to a json file.
-            write_trace_json(voltage.at(0));
         }
+        // Write the samples to a json file.
+        write_trace_json(voltage.at(0));
 
         auto profile = arb::profile::profiler_summary();
         std::cout << profile << "\n";
diff --git a/example/gap_junctions/gap_junctions.cpp b/example/gap_junctions/gap_junctions.cpp
index ccc3fcd760..5ccd732a36 100644
--- a/example/gap_junctions/gap_junctions.cpp
+++ b/example/gap_junctions/gap_junctions.cpp
@@ -133,6 +133,7 @@ class gj_recipe: public arb::recipe {
 };
 
 int main(int argc, char** argv) {
+    int rank = 0;    
     try {
         bool root = true;
 
@@ -142,8 +143,7 @@ int main(int argc, char** argv) {
         int gpu_id = arbenv::find_private_gpu(MPI_COMM_WORLD);
         auto context = arb::make_context(arb::proc_allocation{nt, gpu_id}, MPI_COMM_WORLD);
         {
-            int rank;
-            MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+            rank = arb::rank(context);
             root = rank==0;
         }
 #else
@@ -191,12 +191,9 @@ int main(int argc, char** argv) {
 
         // Set up recording of spikes to a vector on the root process.
         std::vector<arb::spike> recorded_spikes;
-        if (root) {
-            sim.set_global_spike_callback(
-                [&recorded_spikes](const std::vector<arb::spike>& spikes) {
-                    recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                });
-        }
+        sim.set_local_spike_callback([&recorded_spikes](const std::vector<arb::spike>& spikes) {
+            recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+        });
 
         meters.checkpoint("model-init", context);
 
@@ -210,20 +207,19 @@ int main(int argc, char** argv) {
 
         // Write spikes to file
         if (root) {
-            std::cout << "\n" << ns << " spikes generated at rate of "
-                      << params.sim_duration/ns << " ms between spikes\n";
-            std::ofstream fid("spikes.gdf");
-            if (!fid.good()) {
-                std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
-            }
-            else {
-                char linebuf[45];
-                for (auto spike: recorded_spikes) {
-                    auto n = std::snprintf(
-                        linebuf, sizeof(linebuf), "%u %.4f\n",
-                        unsigned{spike.source.gid}, float(spike.time));
-                    fid.write(linebuf, n);
-                }
+            std::cout << "\n" << ns << " spikes generated at rate of " << params.sim_duration/ns << " ms between spikes\n";
+        }
+        std::ofstream fid("spikes-" + std::to_string(rank) + ".gdf");
+        if (!fid.good()) {
+            std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
+        }
+        else {
+            char linebuf[45];
+            for (auto spike: recorded_spikes) {
+                auto n = std::snprintf(linebuf, sizeof(linebuf),
+                                       "%u %.4f\n",
+                                       unsigned{spike.source.gid}, float(spike.time));
+                fid.write(linebuf, n);
             }
         }
 
diff --git a/example/network_description/network_description.cpp b/example/network_description/network_description.cpp
index 8f80814be7..8cc7147fbe 100644
--- a/example/network_description/network_description.cpp
+++ b/example/network_description/network_description.cpp
@@ -9,7 +9,6 @@
 #include <fstream>
 #include <iomanip>
 #include <iostream>
-#include <random>
 #include <vector>
 
 #include <nlohmann/json.hpp>
@@ -60,7 +59,6 @@ ring_params read_options(int argc, char** argv);
 using arb::cell_gid_type;
 using arb::cell_kind;
 using arb::cell_lid_type;
-using arb::cell_member_type;
 using arb::cell_size_type;
 using arb::time_type;
 
@@ -165,6 +163,7 @@ class ring_recipe: public arb::recipe {
 
 int main(int argc, char** argv) {
     try {
+        int rank = 0;
         bool root = true;
 
         arb::proc_allocation resources;
@@ -174,7 +173,8 @@ int main(int argc, char** argv) {
         arbenv::with_mpi guard(argc, argv, false);
         resources.gpu_id = arbenv::find_private_gpu(MPI_COMM_WORLD);
         auto context = arb::make_context(resources, MPI_COMM_WORLD);
-        root = arb::rank(context) == 0;
+        rank = arb::rank(context);
+        root = rank == 0;
 #else
         resources.gpu_id = arbenv::default_gpu();
         auto context = arb::make_context(resources);
@@ -217,12 +217,9 @@ int main(int argc, char** argv) {
 
         // Set up recording of spikes to a vector on the root process.
         std::vector<arb::spike> recorded_spikes;
-        if (root) {
-            sim.set_global_spike_callback(
-                [&recorded_spikes](const std::vector<arb::spike>& spikes) {
-                    recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                });
-        }
+        sim.set_local_spike_callback([&recorded_spikes](const std::vector<arb::spike>& spikes) {
+            recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+        });
 
         meters.checkpoint("model-init", context);
 
@@ -250,21 +247,14 @@ int main(int argc, char** argv) {
             std::cout << "\n"
                       << ns << " spikes generated at rate of " << params.duration / ns
                       << " ms between spikes\n";
-            std::ofstream fid("spikes.gdf");
-            if (!fid.good()) {
-                std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
-            }
-            else {
-                char linebuf[45];
-                for (auto spike: recorded_spikes) {
-                    auto n = std::snprintf(linebuf,
-                        sizeof(linebuf),
-                        "%u %.4f\n",
-                        unsigned{spike.source.gid},
-                        float(spike.time));
-                    fid.write(linebuf, n);
-                }
-            }
+        }
+        std::ofstream fid("spikes-" + std::to_string(rank) + ".gdf");
+        if (!fid.good()) std::cerr << "Warning: unable to open file spikes.gdf for spike output\n";
+        char linebuf[45];
+        for (auto spike: recorded_spikes) {
+            auto n = std::snprintf(linebuf, sizeof(linebuf),
+                                   "%u %.4f\n", unsigned{spike.source.gid}, float(spike.time));
+            fid.write(linebuf, n);
         }
 
         // Write the samples to a json file.
diff --git a/example/plasticity/plasticity.cpp b/example/plasticity/plasticity.cpp
index 110cfb6f39..5ad3ed61b2 100644
--- a/example/plasticity/plasticity.cpp
+++ b/example/plasticity/plasticity.cpp
@@ -113,7 +113,7 @@ int main(int argc, char** argv) {
     auto ctx = arb::make_context(arb::proc_allocation{8, -1});
     auto sim = arb::simulation(rec, ctx);
     sim.add_sampler(arb::all_probes, arb::regular_schedule(dt*arb::units::ms), sampler);
-    sim.set_global_spike_callback(spike_cb);
+    sim.set_local_spike_callback(spike_cb);
     print_header(0, 1);
     sim.run(1.0*arb::units::ms, dt*arb::units::ms);
     rec.add_connection(2);
diff --git a/example/ring/ring.cpp b/example/ring/ring.cpp
index db488dfcd4..822aa79314 100644
--- a/example/ring/ring.cpp
+++ b/example/ring/ring.cpp
@@ -171,12 +171,9 @@ int main(int argc, char** argv) {
 
         // Set up recording of spikes to a vector on the root process.
         std::vector<arb::spike> recorded_spikes;
-        if (root) {
-            sim.set_global_spike_callback(
-                [&recorded_spikes](const std::vector<arb::spike>& spikes) {
-                    recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
-                });
-        }
+        sim.set_local_spike_callback([&recorded_spikes](const std::vector<arb::spike>& spikes) {
+            recorded_spikes.insert(recorded_spikes.end(), spikes.begin(), spikes.end());
+        });
 
         meters.checkpoint("model-init", context);
 
diff --git a/python/simulation.cpp b/python/simulation.cpp
index ea23429fa3..9166ba0b53 100644
--- a/python/simulation.cpp
+++ b/python/simulation.cpp
@@ -136,17 +136,11 @@ class simulation_shim {
 
         switch (policy) {
         case spike_recording::off:
-            sim_->set_global_spike_callback();
             sim_->set_local_spike_callback();
             break;
         case spike_recording::local:
-            sim_->set_global_spike_callback();
             sim_->set_local_spike_callback(spike_recorder);
             break;
-        case spike_recording::all:
-            sim_->set_global_spike_callback(spike_recorder);
-            sim_->set_local_spike_callback();
-            break;
         }
     }
 
diff --git a/test/unit/test_adex_cell_group.cpp b/test/unit/test_adex_cell_group.cpp
index 5783d96925..40a882221e 100644
--- a/test/unit/test_adex_cell_group.cpp
+++ b/test/unit/test_adex_cell_group.cpp
@@ -177,7 +177,7 @@ TEST(adex_cell_group, ring)
 
     std::vector<arb::spike> spike_buffer;
 
-    sim.set_global_spike_callback(
+    sim.set_local_spike_callback(
         [&spike_buffer](const std::vector<arb::spike>& spikes) {
             spike_buffer.insert(spike_buffer.end(), spikes.begin(), spikes.end());
         }
@@ -236,7 +236,7 @@ TEST(adex_cell_group, probe) {
 
     std::vector<arb::spike> spikes;
 
-    sim.set_global_spike_callback([&spikes](const std::vector<arb::spike>& spk) {
+    sim.set_local_spike_callback([&spikes](const std::vector<arb::spike>& spk) {
         for (const auto& s: spk) spikes.push_back(s);
     });
 
@@ -648,8 +648,8 @@ TEST(adex_cell_group, probe) {
     ASSERT_FALSE(testing::seq_eq(ums[{1, "a"}], exp));
     // now check the spikes
     std::sort(spikes.begin(), spikes.end());
-    EXPECT_EQ(spikes.size(), 0u);
-    std::vector<arb::spike> sexp{};
+    EXPECT_EQ(spikes.size(), 6u);
+    std::vector<arb::spike> sexp{{{0, 0}, 2}, {{0, 0}, 3}, {{0, 0}, 4}, {{0, 0}, 5}, {{1, 0}, 2}, {{1, 0}, 5}};
     ASSERT_EQ(spikes, sexp);
 }
 
@@ -671,7 +671,7 @@ TEST(adex_cell_group, probe_with_connections) {
 
     std::vector<arb::spike> spikes;
 
-    sim.set_global_spike_callback(
+    sim.set_local_spike_callback(
         [&spikes](const std::vector<arb::spike>& spk) { for (const auto& s: spk) spikes.push_back(s); }
     );
 
@@ -1085,7 +1085,7 @@ TEST(adex_cell_group, probe_with_connections) {
     ASSERT_FALSE(testing::seq_eq(ums[{1, "a"}], exp));
     // now check the spikes
     std::sort(spikes.begin(), spikes.end());
-    EXPECT_EQ(spikes.size(), 4u);
-    std::vector<arb::spike> sexp{{{0, 0}, 2}, {{0, 0}, 3}, {{0, 0}, 4}, {{0, 0}, 5},};
+    EXPECT_EQ(spikes.size(), 6u);
+    std::vector<arb::spike> sexp{{{0, 0}, 2}, {{0, 0}, 3}, {{0, 0}, 4}, {{0, 0}, 5}, {{1, 0}, 2}, {{1, 0}, 5}};
     ASSERT_EQ(spikes, sexp);
 }
diff --git a/test/unit/test_lif_cell_group.cpp b/test/unit/test_lif_cell_group.cpp
index 624ec4f53f..614dd39a2c 100644
--- a/test/unit/test_lif_cell_group.cpp
+++ b/test/unit/test_lif_cell_group.cpp
@@ -202,7 +202,7 @@ TEST(lif_cell_group, ring)
 
     std::vector<spike> spike_buffer;
 
-    sim.set_global_spike_callback(
+    sim.set_local_spike_callback(
         [&spike_buffer](const std::vector<spike>& spikes) {
             spike_buffer.insert(spike_buffer.end(), spikes.begin(), spikes.end());
         }
@@ -696,7 +696,7 @@ TEST(lif_cell_group, probe_with_connections) {
 
     std::vector<double> spikes;
 
-    sim.set_global_spike_callback(
+    sim.set_local_spike_callback(
         [&spikes](const std::vector<spike>& spk) { for (const auto& s: spk) spikes.push_back(s.time); }
     );
 
diff --git a/test/unit/test_simulation.cpp b/test/unit/test_simulation.cpp
index ea29be92a8..3527e153d9 100644
--- a/test/unit/test_simulation.cpp
+++ b/test/unit/test_simulation.cpp
@@ -76,7 +76,7 @@ TEST(simulation, null_builder) {
     }
 }
 
-TEST(simulation, spike_global_callback) {
+TEST(simulation, spike_local_callback) {
     constexpr unsigned n = 5;
     double t_max = 10.;
 
@@ -175,7 +175,7 @@ TEST(simulation, restart) {
     simulation sim(rec, ctx, decomp);
 
     std::vector<spike> collected;
-    sim.set_global_spike_callback([&](const std::vector<spike>& spikes) {
+    sim.set_local_spike_callback([&](const std::vector<spike>& spikes) {
         collected.insert(collected.end(), spikes.begin(), spikes.end());
     });
 
diff --git a/test/unit/test_spikes.cpp b/test/unit/test_spikes.cpp
index cceb3d20de..f71e989b82 100644
--- a/test/unit/test_spikes.cpp
+++ b/test/unit/test_spikes.cpp
@@ -232,7 +232,7 @@ TEST(SPIKES_TEST_CLASS, threshold_watcher_interpolation) {
         auto decomp = arb::partition_load_balance(rec, context);
         arb::simulation sim(rec, context, decomp);
 
-        sim.set_global_spike_callback(
+        sim.set_local_spike_callback(
                 [&spikes](const std::vector<arb::spike>& recorded_spikes) {
                     spikes.insert(spikes.end(), recorded_spikes.begin(), recorded_spikes.end());
                 });

From 6523bab908171cce66093df0148ed2517069ea43 Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Fri, 29 May 2026 09:18:55 +0200
Subject: [PATCH 4/5] re-scope `root`

---
 example/brunel/brunel.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/example/brunel/brunel.cpp b/example/brunel/brunel.cpp
index c40657a26b..db0d632e84 100644
--- a/example/brunel/brunel.cpp
+++ b/example/brunel/brunel.cpp
@@ -244,8 +244,8 @@ struct brunel_recipe: public recipe {
 };
 
 int main(int argc, char** argv) {
+    bool root = true;
     try {
-        bool root = true;
         int rank = 0;
 #ifdef ARB_MPI_ENABLED
         arbenv::with_mpi guard(argc, argv, false);

From eec4f3cfeaee1a0eaf76e0e2f86db2ce19250e97 Mon Sep 17 00:00:00 2001
From: Thorsten Hater <24411438+thorstenhater@users.noreply.github.com>
Date: Fri, 29 May 2026 09:36:09 +0200
Subject: [PATCH 5/5] Format.

---
 python/example/network_ring_mpi.py           |  6 ++++--
 python/example/single_cell_bluepyopt_l5pc.py | 16 +++++++++-------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/python/example/network_ring_mpi.py b/python/example/network_ring_mpi.py
index 7858799d22..73b3899a16 100644
--- a/python/example/network_ring_mpi.py
+++ b/python/example/network_ring_mpi.py
@@ -114,7 +114,7 @@ def event_generators(self, gid):
 
     # (10) Place a probe at the root of each cell.
     def probes(self, gid):
-        return [A.cable_probe_membrane_voltage('"root"', tag='Um')]
+        return [A.cable_probe_membrane_voltage('"root"', tag="Um")]
 
     def global_properties(self, kind):
         return self.props
@@ -139,7 +139,9 @@ def global_properties(self, kind):
 
 # (15) Attach a sampler to the voltage probe on cell 0. Sample rate of 1 sample every ms.
 # Sampling period increased w.r.t network_ring.py to reduce amount of data
-handles = [sim.sample((gid, 'Um'), A.regular_schedule(1 * U.ms)) for gid in range(ncells)]
+handles = [
+    sim.sample((gid, "Um"), A.regular_schedule(1 * U.ms)) for gid in range(ncells)
+]
 
 # (16) Run simulation
 sim.run(ncells * 5 * U.ms)
diff --git a/python/example/single_cell_bluepyopt_l5pc.py b/python/example/single_cell_bluepyopt_l5pc.py
index b6143c38a2..f5ffd40ce1 100755
--- a/python/example/single_cell_bluepyopt_l5pc.py
+++ b/python/example/single_cell_bluepyopt_l5pc.py
@@ -29,19 +29,21 @@
 )
 
 # (3) Define stimulus and spike detector, adjust discretization
-decor.place('"soma_center"', A.i_clamp(tstart=295*U.ms, duration=5*U.ms, current=1.9*U.nA))
+decor.place(
+    '"soma_center"', A.i_clamp(tstart=295 * U.ms, duration=5 * U.ms, current=1.9 * U.nA)
+)
 
 # Add spike detector
-decor.place('"soma_center"', A.threshold_detector(-10*U.mV), "detector")
+decor.place('"soma_center"', A.threshold_detector(-10 * U.mV), "detector")
 
 # Adjust discretization (single CV on soma, default everywhere else)
-cvp = A.cv_policy_max_extent_um(1.0*U.um) | A.cv_policy_single('"soma"')
+cvp = A.cv_policy_max_extent_um(1.0 * U.um) | A.cv_policy_single('"soma"')
 
 # (4) Create the cell.
 cell = A.cable_cell(morpho, decor, labels, cvp)
 
 # (5) Declare a probe.
-probe = A.cable_probe_membrane_voltage('"dend1"', tag='Um')
+probe = A.cable_probe_membrane_voltage('"dend1"', tag="Um")
 
 
 # (6) Create a class that inherits from A.recipe
@@ -92,11 +94,11 @@ def global_properties(self, gid):
 # Instruct the simulation to record the spikes and sample the probe
 sim.record(A.spike_recording.all)
 
-probe_id = A.cell_member(0, 'Um')
-handle = sim.sample(probe_id, A.regular_schedule(0.02*U.ms))
+probe_id = A.cell_member(0, "Um")
+handle = sim.sample(probe_id, A.regular_schedule(0.02 * U.ms))
 
 # (8) Run the simulation
-sim.run(tfinal=600*U.ms, dt=0.025*U.ms)
+sim.run(tfinal=600 * U.ms, dt=0.025 * U.ms)
 
 # (9) Print or display the results
 spikes = sim.spikes()