diff --git a/src/config.rs b/src/config.rs
index e1ebaa06..f65f9a61 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -8,7 +8,7 @@ pub struct Config {
     /// Setting this to false will reduce the performance impact on the target
     /// python process, but can lead to incorrect results like partial stack
     /// traces being returned or a higher sampling error rate
-    pub non_blocking: bool,
+    pub blocking: LockingStrategy,
 
     /// Whether or not to profile native extensions. Note: this option can not be
     /// used with the nonblocking option, as we have to pause the process to collect
@@ -60,6 +60,14 @@ arg_enum!{
     }
 }
 
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum LockingStrategy {
+    NonBlocking,
+    AlreadyLocked,
+    Lock
+}
+
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub enum RecordDuration {
     Unlimited,
@@ -72,7 +80,7 @@ impl Default for Config {
     fn default() -> Config {
         Config{pid: None, python_program: None, filename: None, format: None,
                command: String::from("top"),
-               non_blocking: false, show_line_numbers: false, sampling_rate: 100,
+               blocking: LockingStrategy::Lock, show_line_numbers: false, sampling_rate: 100,
                duration: RecordDuration::Unlimited, native: false,
                gil_only: false, include_idle: false, include_thread_ids: false,
                hide_progress: false, capture_output: true, dump_json: false, dump_locals: false, subprocesses: false}
@@ -259,7 +267,6 @@ impl Config {
         config.gil_only = matches.occurrences_of("gil") > 0;
         config.include_thread_ids = matches.occurrences_of("threads") > 0;
 
-        config.non_blocking = matches.occurrences_of("nonblocking") > 0;
         config.native = matches.occurrences_of("native") > 0;
         config.hide_progress = matches.occurrences_of("hideprogress") > 0;
         config.dump_json = matches.occurrences_of("json") > 0;
@@ -271,10 +278,13 @@ impl Config {
             config.hide_progress = true;
         }
 
-        // disable native profiling if invalidly asked for
-        if config.native && config.non_blocking {
-            eprintln!("Can't get native stack traces with the --nonblocking option.");
-            std::process::exit(1);
+        if matches.occurrences_of("nonblocking") > 0 {
+            // disable native profiling if invalidly asked for
+            if config.native  {
+                eprintln!("Can't get native stack traces with the --nonblocking option.");
+                std::process::exit(1);
+            }
+            config.blocking = LockingStrategy::NonBlocking;
         }
 
         #[cfg(windows)]
diff --git a/src/lib.rs b/src/lib.rs
index c66949c9..1eb96fbd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -49,8 +49,8 @@ extern crate rand;
 extern crate rand_distr;
 extern crate remoteprocess;
 
-mod config;
-mod binary_parser;
+pub mod config;
+pub mod binary_parser;
 #[cfg(unwind)]
 mod cython;
 #[cfg(unwind)]
diff --git a/src/native_stack_trace.rs b/src/native_stack_trace.rs
index 92c9bfcf..6ac11c07 100644
--- a/src/native_stack_trace.rs
+++ b/src/native_stack_trace.rs
@@ -35,7 +35,7 @@ impl NativeStack {
                               python,
                               libpython,
                               process,
-                              symbol_cache: LruCache::new(4096)
+                              symbol_cache: LruCache::new(65536)
                               });
     }
 
diff --git a/src/python_spy.rs b/src/python_spy.rs
index 43bfe34a..fb2db4a0 100644
--- a/src/python_spy.rs
+++ b/src/python_spy.rs
@@ -17,7 +17,7 @@ use proc_maps::{get_process_maps, MapRange};
 
 
 use crate::binary_parser::{parse_binary, BinaryInfo};
-use crate::config::Config;
+use crate::config::{Config, LockingStrategy};
 #[cfg(unwind)]
 use crate::native_stack_trace::NativeStack;
 use crate::python_bindings::{pyruntime, v2_7_15, v3_3_7, v3_5_5, v3_6_6, v3_7_0, v3_8_0};
@@ -186,10 +186,10 @@ impl PythonSpy {
         // activity status from the OS (otherwise each thread would report being inactive always).
         // This has the potential for race conditions (in that the thread activity could change
         // between getting the status and locking the thread, but seems unavoidable right now
-        let _lock = if self.config.non_blocking {
-            None
-        } else {
+        let _lock = if self.config.blocking == LockingStrategy::Lock {
             Some(self.process.lock().context("Failed to suspend process")?)
+        } else {
+            None
         };
 
         let gil_thread_id = self._get_gil_threadid::<I>()?;
@@ -329,7 +329,7 @@ impl PythonSpy {
     fn _get_os_thread_id<I: InterpreterState>(&mut self, python_thread_id: u64, interp: &I) -> Result<Option<Tid>, Error> {
         // in nonblocking mode, we can't get the threadid reliably (method here requires reading the RBX
         // register which requires a ptrace attach). fallback to heuristic thread activity here
-        if self.config.non_blocking {
+        if self.config.blocking == LockingStrategy::NonBlocking {
             return Ok(None);
         }