feat: thread pool

library/libsds.nim

@@ -5,7 +5,7 @@
 when defined(linux):
   {.passl: "-Wl,-soname,libsds.so".}
 
-import std/[typetraits, tables, atomics], chronos, chronicles
+import std/[typetraits, tables, atomics, locks], chronos, chronicles
 import
   ./sds_thread/sds_thread,
   ./alloc,
@@ -57,6 +57,29 @@ template callEventCallback(ctx: ptr SdsContext, eventName: string, body: untyped
         RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), ctx[].eventUserData
       )
 
+var
+  ctxPool: seq[ptr SdsContext]
+  ctxPoolLock: Lock
+
+proc acquireCtx(callback: SdsCallBack, userData: pointer): ptr SdsContext =
+  ctxPoolLock.acquire()
+  defer: ctxPoolLock.release()
+  if ctxPool.len > 0:
+    result = ctxPool.pop()
+  else:
+    result = sds_thread.createSdsThread().valueOr:
+      let msg = "Error in createSdsThread: " & $error
+      callback(RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), userData)
+      return nil
+
+proc releaseCtx(ctx: ptr SdsContext) =
+  ctxPoolLock.acquire()
+  defer: ctxPoolLock.release()
+  ctx.userData = nil
+  ctx.eventCallback = nil
+  ctx.eventUserData = nil
+  ctxPool.add(ctx)
+
 proc handleRequest(
     ctx: ptr SdsContext,
     requestType: RequestType,
@@ -140,10 +163,9 @@ proc SdsNewReliabilityManager(
     echo "error: missing callback in NewReliabilityManager"
     return nil
 
-  ## Create the SDS thread that will keep waiting for req from the main thread.
-  var ctx = sds_thread.createSdsThread().valueOr:
-    let msg = "Error in createSdsThread: " & $error
-    callback(RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), userData)
+  ## Create or reuse the SDS thread that will keep waiting for req from the main thread.
+  var ctx = acquireCtx(callback, userData)
+  if ctx.isNil():
     return nil
 
   ctx.userData = userData
@@ -183,14 +205,20 @@ proc SdsCleanupReliabilityManager(
   initializeLibrary()
   checkLibsdsParams(ctx, callback, userData)
 
-  sds_thread.destroySdsThread(ctx).isOkOr:
-    let msg = "libsds error: " & $error
-    callback(RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), userData)
+  let resetRes = handleRequest(
+    ctx,
+    RequestType.LIFECYCLE,
+    SdsLifecycleRequest.createShared(SdsLifecycleMsgType.RESET_RELIABILITY_MANAGER),
+    callback,
+    userData,
+  )
+
+  if resetRes == RET_ERR:
     return RET_ERR
 
-  ## always need to invoke the callback although we don't retrieve value to the caller
-  callback(RET_OK, nil, 0, userData)
+  releaseCtx(ctx)
 
+  # handleRequest already invoked the callback; nothing else to signal here.
   return RET_OK
 
 proc SdsResetReliabilityManager(