diff --git a/copyparty/__main__.py b/copyparty/__main__.py
index ac78f973..35862370 100644
--- a/copyparty/__main__.py
+++ b/copyparty/__main__.py
@@ -344,6 +344,8 @@ def run_argparse(argv, formatter):
     ap2.add_argument("--dotpart", action="store_true", help="dotfile incomplete uploads")
     ap2.add_argument("--sparse", metavar="MiB", type=int, default=4, help="up2k min.size threshold (mswin-only)")
     ap2.add_argument("--unpost", metavar="SEC", type=int, default=3600*12, help="grace period where uploads can be deleted by the uploader, even without delete permissions; 0=disabled")
+    ap2.add_argument("--no-fpool", action="store_true", help="disable file-handle pooling -- instead, repeatedly close and reopen files during upload")
+    ap2.add_argument("--use-fpool", action="store_true", help="force file-handle pooling, even if copyparty thinks you're better off without")
 
     ap2 = ap.add_argument_group('network options')
     ap2.add_argument("-i", metavar="IP", type=u, default="0.0.0.0", help="ip to bind (comma-sep.)")
diff --git a/copyparty/httpcli.py b/copyparty/httpcli.py
index 5160f43d..462aa194 100644
--- a/copyparty/httpcli.py
+++ b/copyparty/httpcli.py
@@ -39,6 +39,7 @@ class HttpCli(object):
     def __init__(self, conn):
         self.t0 = time.time()
         self.conn = conn
+        self.mutex = conn.mutex
         self.s = conn.s  # type: socket
         self.sr = conn.sr  # type: Unrecv
         self.ip = conn.addr[0]
@@ -47,6 +48,7 @@ class HttpCli(object):
         self.asrv = conn.asrv  # type: AuthSrv
         self.ico = conn.ico
         self.thumbcli = conn.thumbcli
+        self.u2fh = conn.u2fh
         self.log_func = conn.log_func
         self.log_src = conn.log_src
         self.tls = hasattr(self.s, "cipher")
@@ -835,7 +837,18 @@ class HttpCli(object):
 
         reader = read_socket(self.sr, remains)
 
-        with open(fsenc(path), "rb+", 512 * 1024) as f:
+        f = None
+        fpool = not self.args.no_fpool
+        if fpool:
+            with self.mutex:
+                try:
+                    f = self.u2fh.pop(path)
+                except:
+                    pass
+
+        f = f or open(fsenc(path), "rb+", 512 * 1024)
+
+        try:
             f.seek(cstart[0])
             post_sz, _, sha_b64 = hashcopy(reader, f)
 
@@ -865,22 +878,36 @@ class HttpCli(object):
                     ofs += len(buf)
 
                 self.log("clone {} done".format(cstart[0]))
+        finally:
+            if not fpool:
+                f.close()
+            else:
+                with self.mutex:
+                    self.u2fh.put(path, f)
 
         x = self.conn.hsrv.broker.put(True, "up2k.confirm_chunk", ptop, wark, chash)
         x = x.get()
         try:
-            num_left, path = x
+            num_left, fin_path = x
         except:
             self.loud_reply(x, status=500)
             return False
 
-        if not ANYWIN and num_left == 0:
+        if not num_left and fpool:
+            with self.mutex:
+                self.u2fh.close(path)
+        
+        # windows cant rename open files
+        if ANYWIN and path != fin_path and not self.args.nw:
+            self.conn.hsrv.broker.put(True, "up2k.finish_upload", ptop, wark).get()
+
+        if not ANYWIN and not num_left:
             times = (int(time.time()), int(lastmod))
             self.log("no more chunks, setting times {}".format(times))
             try:
-                bos.utime(path, times)
+                bos.utime(fin_path, times)
             except:
-                self.log("failed to utime ({}, {})".format(path, times))
+                self.log("failed to utime ({}, {})".format(fin_path, times))
 
         spd = self._spd(post_sz)
         self.log("{} thank".format(spd))
diff --git a/copyparty/httpconn.py b/copyparty/httpconn.py
index 32681640..7967e481 100644
--- a/copyparty/httpconn.py
+++ b/copyparty/httpconn.py
@@ -32,9 +32,11 @@ class HttpConn(object):
         self.addr = addr
         self.hsrv = hsrv
 
+        self.mutex = hsrv.mutex
         self.args = hsrv.args
         self.asrv = hsrv.asrv
         self.cert_path = hsrv.cert_path
+        self.u2fh = hsrv.u2fh
 
         enth = HAVE_PIL and not self.args.no_thumb
         self.thumbcli = ThumbCli(hsrv.broker) if enth else None
diff --git a/copyparty/httpsrv.py b/copyparty/httpsrv.py
index fe0d5534..b227ab78 100644
--- a/copyparty/httpsrv.py
+++ b/copyparty/httpsrv.py
@@ -27,7 +27,7 @@ except ImportError:
     sys.exit(1)
 
 from .__init__ import E, PY2, MACOS
-from .util import spack, min_ex, start_stackmon, start_log_thrs
+from .util import FHC, spack, min_ex, start_stackmon, start_log_thrs
 from .bos import bos
 from .httpconn import HttpConn
 
@@ -50,7 +50,10 @@ class HttpSrv(object):
         self.log = broker.log
         self.asrv = broker.asrv
 
-        self.name = "httpsrv" + ("-n{}-i{:x}".format(nid, os.getpid()) if nid else "")
+        nsuf = "-{}".format(nid) if nid else ""
+        nsuf2 = "-n{}-i{:x}".format(nid, os.getpid()) if nid else ""
+
+        self.name = "hsrv" + nsuf2
         self.mutex = threading.Lock()
         self.stopping = False
 
@@ -59,6 +62,7 @@ class HttpSrv(object):
         self.tp_time = None  # latest worker collect
         self.tp_q = None if self.args.no_htp else queue.LifoQueue()
 
+        self.u2fh = FHC()
         self.srvs = []
         self.ncli = 0  # exact
         self.clients = {}  # laggy
@@ -82,11 +86,6 @@ class HttpSrv(object):
         if self.tp_q:
             self.start_threads(4)
 
-            name = "httpsrv-scaler" + ("-{}".format(nid) if nid else "")
-            t = threading.Thread(target=self.thr_scaler, name=name)
-            t.daemon = True
-            t.start()
-
         if nid:
             if self.args.stackmon:
                 start_stackmon(self.args.stackmon, nid)
@@ -94,6 +93,10 @@ class HttpSrv(object):
             if self.args.log_thrs:
                 start_log_thrs(self.log, self.args.log_thrs, nid)
 
+        t = threading.Thread(target=self.periodic, name="hsrv-pt" + nsuf)
+        t.daemon = True
+        t.start()
+
     def start_threads(self, n):
         self.tp_nthr += n
         if self.args.log_htp:
@@ -115,13 +118,15 @@ class HttpSrv(object):
         for _ in range(n):
             self.tp_q.put(None)
 
-    def thr_scaler(self):
+    def periodic(self):
         while True:
-            time.sleep(2 if self.tp_ncli else 30)
+            time.sleep(2 if self.tp_ncli else 10)
             with self.mutex:
-                self.tp_ncli = max(self.ncli, self.tp_ncli - 2)
-                if self.tp_nthr > self.tp_ncli + 8:
-                    self.stop_threads(4)
+                self.u2fh.clean()
+                if self.tp_q:
+                    self.tp_ncli = max(self.ncli, self.tp_ncli - 2)
+                    if self.tp_nthr > self.tp_ncli + 8:
+                        self.stop_threads(4)
 
     def listen(self, sck, nlisteners):
         ip, port = sck.getsockname()
diff --git a/copyparty/svchub.py b/copyparty/svchub.py
index 232f0c12..9b3b21f9 100644
--- a/copyparty/svchub.py
+++ b/copyparty/svchub.py
@@ -53,6 +53,17 @@ class SvcHub(object):
         if args.log_thrs:
             start_log_thrs(self.log, args.log_thrs, 0)
 
+        if not ANYWIN and not args.use_fpool:
+            args.no_fpool = True
+
+        if not args.no_fpool and args.j != 1:
+            m = "WARNING: --use-fpool combined with multithreading is untested and can probably cause undefined behavior"
+            if ANYWIN:
+                m = "windows cannot do multithreading without --no-fpool, so enabling that -- note that upload performance will suffer if you have microsoft defender \"real-time protection\" enabled, so you probably want to use -j 1 instead"
+                args.no_fpool = True
+            
+            self.log("root", m, c=3)
+
         # initiate all services to manage
         self.asrv = AuthSrv(self.args, self.log)
         if args.ls:
diff --git a/copyparty/up2k.py b/copyparty/up2k.py
index 21c7fe11..ba3c8767 100644
--- a/copyparty/up2k.py
+++ b/copyparty/up2k.py
@@ -1336,6 +1336,22 @@ class Up2k(object):
                 # del self.registry[ptop][wark]
                 return ret, dst
 
+        # windows cant rename open files
+        if not ANYWIN or src == dst:
+            self.finish_upload(ptop, wark)
+
+        return ret, dst
+
+    def finish_upload(self, ptop, wark):
+        with self.mutex:
+            try:
+                job = self.registry[ptop][wark]
+                pdir = os.path.join(job["ptop"], job["prel"])
+                src = os.path.join(pdir, job["tnam"])
+                dst = os.path.join(pdir, job["name"])
+            except Exception as ex:
+                return "finish_upload, wark, " + repr(ex)
+
             atomic_move(src, dst)
 
             if ANYWIN:
@@ -1348,8 +1364,6 @@ class Up2k(object):
                 del self.registry[ptop][wark]
                 # in-memory registry is reserved for unfinished uploads
 
-        return ret, dst
-
     def idx_wark(self, ptop, wark, rd, fn, lmod, sz, ip, at):
         cur = self.cur.get(ptop)
         if not cur:
diff --git a/copyparty/util.py b/copyparty/util.py
index ffcc8a7c..abf63994 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -251,6 +251,55 @@ class _LUnrecv(object):
 Unrecv = _Unrecv
 
 
+class FHC(object):
+    class CE(object):
+        def __init__(self, fh):
+            self.ts = 0
+            self.fhs = [fh]
+
+    def __init__(self):
+        self.cache = {}
+
+    def close(self, path):
+        try:
+            ce = self.cache[path]
+        except:
+            return
+
+        for fh in ce.fhs:
+            fh.close()
+
+        del self.cache[path]
+
+    def clean(self):
+        if not self.cache:
+            return
+
+        keep = {}
+        now = time.time()
+        for path, ce in self.cache.items():
+            if now < ce.ts + 5:
+                keep[path] = ce
+            else:
+                for fh in ce.fhs:
+                    fh.close()
+
+        self.cache = keep
+
+    def pop(self, path):
+        return self.cache[path].fhs.pop()
+
+    def put(self, path, fh):
+        try:
+            ce = self.cache[path]
+            ce.fhs.append(fh)
+        except:
+            ce = self.CE(fh)
+            self.cache[path] = ce
+
+        ce.ts = time.time()
+
+
 class ProgressPrinter(threading.Thread):
     """
     periodically print progress info without linefeeds