diff --git a/vm/src/stdlib/thread.rs b/vm/src/stdlib/thread.rs
index 425a3e3f2..1a3ec9a94 100644
--- a/vm/src/stdlib/thread.rs
+++ b/vm/src/stdlib/thread.rs
@@ -4,7 +4,10 @@ use crate::function::{Args, KwArgs, OptionalArg, PyFuncArgs};
 use crate::obj::objdict::PyDictRef;
 use crate::obj::objtuple::PyTupleRef;
 use crate::obj::objtype::PyClassRef;
-use crate::pyobject::{Either, PyCallable, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue};
+use crate::pyobject::{
+    Either, IdProtocol, PyCallable, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue,
+    TypeProtocol,
+};
 use crate::vm::VirtualMachine;
 
 use parking_lot::{
@@ -16,18 +19,20 @@ use std::io::Write;
 use std::time::Duration;
 use std::{fmt, thread};
 
+// PY_TIMEOUT_MAX is a value in microseconds
 #[cfg(not(target_os = "windows"))]
-const PY_TIMEOUT_MAX: isize = std::isize::MAX;
+const PY_TIMEOUT_MAX: isize = std::isize::MAX / 1_000;
 
 #[cfg(target_os = "windows")]
-const PY_TIMEOUT_MAX: isize = 0xffffffff * 1_000_000;
+const PY_TIMEOUT_MAX: isize = 0xffffffff * 1_000;
 
-const TIMEOUT_MAX: f64 = (PY_TIMEOUT_MAX / 1_000_000_000) as f64;
+// this is a value in seconds
+const TIMEOUT_MAX: f64 = (PY_TIMEOUT_MAX / 1_000_000) as f64;
 
 #[derive(FromArgs)]
 struct AcquireArgs {
     #[pyarg(positional_or_keyword, default = "true")]
-    waitflag: bool,
+    blocking: bool,
     #[pyarg(positional_or_keyword, default = "Either::A(-1.0)")]
     timeout: Either<f64, isize>,
 }
@@ -39,7 +44,7 @@ macro_rules! acquire_lock_impl {
             Either::A(f) => f,
             Either::B(i) => i as f64,
         };
-        match args.waitflag {
+        match args.blocking {
             true if timeout == -1.0 => {
                 mu.lock();
                 Ok(true)
@@ -48,7 +53,16 @@ macro_rules! acquire_lock_impl {
                 Err(vm.new_value_error("timeout value must be positive".to_owned()))
             }
             true => {
-                // TODO: respect TIMEOUT_MAX here
+                // modified from std::time::Duration::from_secs_f64 to avoid a panic.
+                // TODO: put this in the Duration::try_from_object impl, maybe?
+                let micros = timeout * 1_000_000.0;
+                let nanos = timeout * 1_000_000_000.0;
+                if micros > PY_TIMEOUT_MAX as f64 || nanos < 0.0 || !nanos.is_finite() {
+                    return Err(vm.new_overflow_error(
+                        "timestamp too large to convert to Rust Duration".to_owned(),
+                    ));
+                }
+
                 Ok(mu.try_lock_for(Duration::from_secs_f64(timeout)))
             }
             false if timeout != -1.0 => {
@@ -59,6 +73,21 @@ macro_rules! acquire_lock_impl {
         }
     }};
 }
+macro_rules! repr_lock_impl {
+    ($zelf:expr) => {{
+        let status = if $zelf.mu.is_locked() {
+            "locked"
+        } else {
+            "unlocked"
+        };
+        format!(
+            "<{} {} object at {}>",
+            status,
+            $zelf.class().name,
+            $zelf.get_id()
+        )
+    }};
+}
 
 #[pyclass(name = "lock")]
 struct PyLock {
@@ -102,6 +131,11 @@ impl PyLock {
     fn locked(&self) -> bool {
         self.mu.is_locked()
     }
+
+    #[pymethod(magic)]
+    fn repr(zelf: PyRef<Self>) -> String {
+        repr_lock_impl!(zelf)
+    }
 }
 
 type RawRMutex = RawReentrantMutex<RawMutex, RawThreadId>;
@@ -149,6 +183,11 @@ impl PyRLock {
     fn exit(&self, _args: PyFuncArgs) {
         self.release()
     }
+
+    #[pymethod(magic)]
+    fn repr(zelf: PyRef<Self>) -> String {
+        repr_lock_impl!(zelf)
+    }
 }
 
 fn thread_get_ident() -> u64 {
@@ -195,12 +234,16 @@ fn thread_start_new_thread(
         }
         SENTINELS.with(|sents| {
             for lock in sents.replace(Default::default()) {
-                lock.release()
+                lock.mu.unlock()
             }
-        })
+        });
+        vm.state.thread_count.fetch_sub(1);
     });
-    res.map(|handle| thread_to_id(&handle.thread()))
-        .map_err(|err| super::os::convert_io_error(vm, err))
+    res.map(|handle| {
+        vm.state.thread_count.fetch_add(1);
+        thread_to_id(&handle.thread())
+    })
+    .map_err(|err| super::os::convert_io_error(vm, err))
 }
 
 thread_local!(static SENTINELS: RefCell<Vec<PyLockRef>> = RefCell::default());
@@ -217,6 +260,10 @@ fn thread_stack_size(size: OptionalArg<usize>, vm: &VirtualMachine) -> usize {
     vm.state.stacksize.swap(size)
 }
 
+fn thread_count(vm: &VirtualMachine) -> usize {
+    vm.state.thread_count.load()
+}
+
 pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
     let ctx = &vm.ctx;
 
@@ -228,6 +275,7 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
         "start_new_thread" => ctx.new_function(thread_start_new_thread),
         "_set_sentinel" => ctx.new_function(thread_set_sentinel),
         "stack_size" => ctx.new_function(thread_stack_size),
+        "_count" => ctx.new_function(thread_count),
         "error" => ctx.exceptions.runtime_error.clone(),
         "TIMEOUT_MAX" => ctx.new_float(TIMEOUT_MAX),
     })
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index ebcf66afa..9bf5e2f70 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -76,6 +76,7 @@ pub struct PyGlobalState {
     pub stdlib_inits: HashMap<String, stdlib::StdlibInitFunc>,
     pub frozen: HashMap<String, bytecode::FrozenModule>,
     pub stacksize: AtomicCell<usize>,
+    pub thread_count: AtomicCell<usize>,
 }
 
 pub const NSIG: usize = 64;
@@ -207,6 +208,7 @@ impl VirtualMachine {
                 stdlib_inits,
                 frozen,
                 stacksize: AtomicCell::new(0),
+                thread_count: AtomicCell::new(0),
             }),
             initialized: false,
         };