feat: thread pool (#40)

* feat: thread pool

* proper pass ARCH in Makefile when building for Android

---------

Co-authored-by: Ivan Folgueira Bande <ivansete@status.im>

Makefile

@@ -115,7 +115,7 @@ build-libsds-for-android-arch: NIM_PARAMS := $(NIM_PARAMS) --passC="-I$(ANDROID_
 build-libsds-for-android-arch: NIM_PARAMS := $(NIM_PARAMS) --passL="-L$(ANDROID_TOOLCHAIN_DIR)/sysroot/usr/lib/$(ARCH_DIRNAME)/$(ANDROID_TARGET)"
 build-libsds-for-android-arch:
 	CC=$(ANDROID_TOOLCHAIN_DIR)/bin/$(ANDROID_ARCH)$(ANDROID_TARGET)-clang \
-	CPU=$(CPU) ABIDIR=$(ABIDIR) \
+	ARCH=$(ARCH) ABIDIR=$(ABIDIR) \
 	ARCH_DIRNAME=$(ARCH_DIRNAME) \
 	ANDROID_ARCH=$(ANDROID_ARCH) \
 	ANDROID_TOOLCHAIN_DIR=$(ANDROID_TOOLCHAIN_DIR) \
@@ -123,37 +123,37 @@ build-libsds-for-android-arch:
 	nim libsdsAndroid $(NIM_PARAMS) sds.nims
 
 libsds-android-arm64: ANDROID_ARCH=aarch64-linux-android
-libsds-android-arm64: CPU=arm64
+libsds-android-arm64: ARCH=arm64
 libsds-android-arm64: ABIDIR=arm64-v8a
 libsds-android-arm64: ARCH_DIRNAME=aarch64-linux-android
 libsds-android-arm64: | libsds-android-precheck build deps
 	$(MAKE) build-libsds-for-android-arch ANDROID_ARCH=$(ANDROID_ARCH) \
-	CPU=$(CPU) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
+	ARCH=$(ARCH) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
 
 libsds-android-amd64: ANDROID_ARCH=x86_64-linux-android
-libsds-android-amd64: CPU=amd64
+libsds-android-amd64: ARCH=amd64
 libsds-android-amd64: ABIDIR=x86_64
 libsds-android-amd64: ARCH_DIRNAME=x86_64-linux-android
 libsds-android-amd64: | libsds-android-precheck build deps
 	$(MAKE) build-libsds-for-android-arch ANDROID_ARCH=$(ANDROID_ARCH) \
-	CPU=$(CPU) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
+	ARCH=$(ARCH) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
 
 libsds-android-x86: ANDROID_ARCH=i686-linux-android
-libsds-android-x86: CPU=i386
+libsds-android-x86: ARCH=i386
 libsds-android-x86: ABIDIR=x86
 libsds-android-x86: ARCH_DIRNAME=i686-linux-android
 libsds-android-x86: | libsds-android-precheck build deps
 	$(MAKE) build-libsds-for-android-arch ANDROID_ARCH=$(ANDROID_ARCH) \
-	CPU=$(CPU) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
+	ARCH=$(ARCH) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME)
 
 libsds-android-arm: ANDROID_ARCH=armv7a-linux-androideabi
-libsds-android-arm: CPU=arm
+libsds-android-arm: ARCH=arm
 libsds-android-arm: ABIDIR=armeabi-v7a
 libsds-android-arm: ARCH_DIRNAME=arm-linux-androideabi
 libsds-android-arm: | libsds-android-precheck build deps
 # cross-rs target architecture name does not match the one used in android
 	$(MAKE) build-libsds-for-android-arch ANDROID_ARCH=$(ANDROID_ARCH) \
-	CPU=$(CPU) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME) \
+	ARCH=$(ARCH) ABIDIR=$(ABIDIR) ARCH_DIRNAME=$(ARCH_DIRNAME) \
 
 libsds-android:
 ifeq ($(ARCH),arm64)

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.
+  ## Create or reuse the SDS thread that will keep waiting for req from the main thread.
-  var ctx = sds_thread.createSdsThread().valueOr:
+  var ctx = acquireCtx(callback, userData)
-    let msg = "Error in createSdsThread: " & $error
+  if ctx.isNil():
-    callback(RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), userData)
     return nil
 
   ctx.userData = userData
@@ -183,14 +205,20 @@ proc SdsCleanupReliabilityManager(
   initializeLibrary()
   checkLibsdsParams(ctx, callback, userData)
 
-  sds_thread.destroySdsThread(ctx).isOkOr:
+  let resetRes = handleRequest(
-    let msg = "libsds error: " & $error
+    ctx,
-    callback(RET_ERR, unsafeAddr msg[0], cast[csize_t](len(msg)), userData)
+    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
+  releaseCtx(ctx)
-  callback(RET_OK, nil, 0, userData)
 
+  # handleRequest already invoked the callback; nothing else to signal here.
   return RET_OK
 
 proc SdsResetReliabilityManager(