diff --git a/tests/test_auxiliary_procs.nim b/tests/test_auxiliary_procs.nim
new file mode 100644
index 0000000..55b632c
--- /dev/null
+++ b/tests/test_auxiliary_procs.nim
@@ -0,0 +1,18 @@
+import
+  std/[atomics, os],
+  ../weave
+
+var count: Atomic[int]
+
+proc increment() = count += 1
+proc decrement() = count -= 1
+
+const ThreadsToLaunch = 8 # Arbitrary value
+
+putEnv("WEAVE_NUM_THREADS", $ThreadsToLaunch)
+
+init(Weave, increment)
+syncRoot(Weave)
+doAssert(count.load == ThreadsToLaunch - 1)
+exit(Weave, decrement)
+doAssert(count.load == 0)
\ No newline at end of file
diff --git a/weave.nimble b/weave.nimble
index 40cb216..4f28e0a 100644
--- a/weave.nimble
+++ b/weave.nimble
@@ -47,6 +47,7 @@ task test, "Run Weave tests":
   test "", "weave/parallel_reduce.nim"
 
   test "--debugger:native", "tests/test_background_jobs.nim"
+  test "--debugger:native", "tests/test_auxiliary_procs.nim"
 
   test "-d:WV_LazyFlowvar", "weave/parallel_tasks.nim"
   test "-d:WV_LazyFlowvar", "weave/parallel_for.nim"
@@ -117,6 +118,7 @@ task test_gc_arc, "Run Weave tests with --gc:arc":
   test "--gc:arc", "weave/parallel_reduce.nim"
 
   test "--gc:arc", "tests/test_background_jobs.nim"
+  test "--gc:arc", "tests/test_auxiliary_procs.nim"
 
   test "--gc:arc -d:WV_LazyFlowvar", "weave/parallel_tasks.nim"
   test "--gc:arc -d:WV_LazyFlowvar", "weave/parallel_for.nim"
diff --git a/weave/datatypes/context_global.nim b/weave/datatypes/context_global.nim
index 184e961..58dc2f6 100644
--- a/weave/datatypes/context_global.nim
+++ b/weave/datatypes/context_global.nim
@@ -50,6 +50,7 @@ type
     barrier*: SyncBarrier
       ## Barrier for initialization and teardown
     manager*: ManagerContext
+    auxiliaryInit*, auxiliaryExit*: proc() {.nimcall, gcsafe.}
 
   ManagerContext* = object
     ## Manager context
diff --git a/weave/runtime.nim b/weave/runtime.nim
index dc63715..a543f8f 100644
--- a/weave/runtime.nim
+++ b/weave/runtime.nim
@@ -29,7 +29,10 @@ else:
 # Runtime public routines
 # ----------------------------------------------------------------------------------
 
-proc init*(_: type Weave) =
+type AuxiliaryProc* = proc() {.nimcall, gcsafe.} | proc() {.cdecl, gcsafe.}
+const WV_NoAuxiliary: proc() {.nimcall, gcsafe.} = nil # for type resolution
+
+proc init*(_: type Weave, auxiliary: AuxiliaryProc = WV_NoAuxiliary) =
   # TODO detect Hyper-Threading and NUMA domain
   manager.acceptsJobs.store(false, moRelaxed)
 
@@ -42,6 +45,11 @@ proc init*(_: type Weave) =
   else:
     workforce() = int32 countProcessors()
 
+  when auxiliary is proc() {.cdecl, gcsafe.}:
+    globalCtx.auxiliaryInit = proc() {.nimcall, gcsafe.} = auxiliary
+  else:
+    globalCtx.auxiliaryInit = auxiliary
+
   ## Allocation of the global context.
   globalCtx.mempools = wv_alloc(TLPoolAllocator, workforce())
   globalCtx.threadpool = wv_alloc(Thread[WorkerID], workforce())
@@ -167,7 +175,12 @@ proc globalCleanup() =
   metrics:
     log("+========================================+\n")
 
-proc exit*(_: type Weave) =
+proc exit*(_: type Weave, auxiliary: AuxiliaryProc = WV_NoAuxiliary) =
+  when auxiliary is proc() {.cdecl, gcsafe.}:
+    globalCtx.auxiliaryExit = proc() {.nimcall, gcsafe.} = auxiliary
+  else:
+    globalCtx.auxiliaryExit = auxiliary
+
   syncRoot(_)
   signalTerminate(nil)
   workerContext.signaledTerminate = true
diff --git a/weave/scheduler.nim b/weave/scheduler.nim
index 92f8089..6fd5a16 100644
--- a/weave/scheduler.nim
+++ b/weave/scheduler.nim
@@ -171,6 +171,11 @@ proc worker_entry_fn*(id: WorkerID) =
   myID() = id # If this crashes, you need --tlsemulation:off
   myMemPool().initialize()
   setupWorker()
+
+  # Unstealable user-definable procedure to be executed on all threads
+  {.gcsafe.}:
+    if not globalCtx.auxiliaryInit.isNil: globalCtx.auxiliaryInit()
+
   discard globalCtx.barrier.wait()
 
   eventLoop()
@@ -181,6 +186,10 @@ proc worker_entry_fn*(id: WorkerID) =
   # 1 matching barrier in init(Runtime) for lead thread
   workerMetrics()
 
+  # Same as auxiliaryInit, but for cleanup
+  {.gcsafe.}:
+    if not globalCtx.auxiliaryExit.isNil: globalCtx.auxiliaryExit()
+
   teardownWorker()
   postCondition: localThreadKind == Unknown