Deloxide - Cross-Language Deadlock Detector

Deloxide is a cross-language deadlock detection library with visualization support. It tracks mutex and reader-writer lock operations in multi-threaded applications to detect, report, and visualize potential deadlocks in real-time.

Table of Contents

• Features
• Building and Installation
• Quick Start
  • Rust
  • C
• Visualization
• Project Architecture
• Lock Order Graph
• Stress Testing
• Comparison with Other Solutions
• Performance & Validation
• Documentation
• License

Features

• Real-time deadlock detection - Detects deadlocks as they happen using a Dual Detection Architecture (WFG + LOG)
• Zero False Positives - Wait-For Graph (WFG) analysis ensures 100% precision for active deadlocks
• Optimistic Fast Path - "Always-on" monitoring with negligible overhead
• Cross-language support - Core implementation in Rust with C bindings
• Stress Testing Framework - Probabilistic scheduling with Component-Based Targeting
• Visual Diagnostics - Serverless, privacy-preserving visualization of thread interactions (see example here)
• Easy integration - Drop-in replacements for parking_lot primitives

Note

Cross-platform support: Rust API works on Windows, macOS, and Linux. The C API is POSIX-first and ships with pthread-based convenience macros for macOS/Linux; on Windows those macros are disabled (see below) but the core C functions are fully usable.

Building and Installation

Rust

Deloxide is available on crates.io. You can add it as a dependency in your Cargo.toml:

[dependencies]
deloxide = "1.0"

With lock order graph:

[dependencies]
deloxide = { version = "1.0", features = ["lock-order-graph"] }

With stress testing:

[dependencies]
deloxide = { version = "1.0", features = ["stress-test"] }

With logging and visualization:

[dependencies]
deloxide = { version = "1.0", features = ["logging-and-visualization"] }

Or install the CLI tool to showcase deadlock logs directly:

cargo install deloxide
deloxide my_deadlock.log  # Opens visualization in browser

For development builds:

# Standard build
cargo build --release

# With lock order graph feature
cargo build --release --features lock-order-graph

# With stress testing feature
cargo build --release --features stress-test

# With both features
cargo build --release --features lock-order-graph,stress-test

C

For C programs, you'll need to compile the Rust library and link against it:

# Build the Rust library
cargo build --release

# With lock order graph feature
cargo build --release --features lock-order-graph

# With stress testing feature
cargo build --release --features stress-test

# With both features
cargo build --release --features lock-order-graph,stress-test

# Compile your C program with Deloxide
gcc -Iinclude your_program.c -Ltarget/release -ldeloxide -lpthread -o your_program

A Makefile is included in the repository to simplify building and testing with C programs. It handles building the Rust library and compiling the C test programs automatically.

C API portability notes

• Thread ID size across FFI

  • The C header uses uintptr_t for all thread IDs; the Rust side uses usize. This ensures correct sizes on LP64 (Linux/macOS) and LLP64 (Windows).

• pthread-based helpers are POSIX-only

  • The convenience macros DEFINE_TRACKED_THREAD and CREATE_TRACKED_THREAD depend on pthread.h and are available only on non-Windows platforms.
  • On Windows, these macros are disabled at compile time. You can still use the full C API by manually registering thread lifecycle events.

• Manual thread registration (Windows or custom runtimes)

  1. Create your thread using your platform's API.
  2. In the thread entry, call deloxide_register_thread_spawn(child_tid, parent_tid) once. On the thread, get IDs from deloxide_get_thread_id().
  3. Before the thread returns, call deloxide_register_thread_exit(current_tid).

  Minimal example sketch (pseudo-C):

  // In parent, capture parent thread id
  uintptr_t parent_tid = deloxide_get_thread_id();
  // Create thread with OS API (e.g., _beginthreadex / CreateThread)
  // In child thread entry:
  uintptr_t child_tid = deloxide_get_thread_id();
  deloxide_register_thread_spawn(child_tid, parent_tid);
  // ... user work ...
  deloxide_register_thread_exit(child_tid);

Quick Start

Rust

Deloxide provides drop-in replacements for parking_lot synchronization primitives with added deadlock detection capabilities. These primitives are API-compatible with parking_lot and serve as near drop-in replacements for std::sync (requiring only the removal of .unwrap() calls since poisoning is not supported).

deloxide::thread

A drop-in replacement for std::thread that automatically tracks thread lifecycle events. All std::thread functions and types are available with added deadlock detection:

// All std::thread items are re-exported
pub use std::thread::{
    AccessError, JoinHandle, LocalKey, Result, Scope, 
    ScopedJoinHandle, Thread, ThreadId, available_parallelism, 
    current, panicking, park, park_timeout, sleep, yield_now,
};

// Custom spawn function with tracking
pub fn spawn<F, T>(f: F) -> JoinHandle<T> 
    where F: FnOnce() -> T + Send + 'static, T: Send + 'static;

// Custom Builder with tracking
pub struct Builder { /* ... */ }

Using tracked threads is identical to using std::thread:

use deloxide::thread;

// Spawn a tracked thread - exactly like std::thread::spawn
let handle = thread::spawn(|| {
    println!("Hello from tracked thread!");
    42
});

// All std::thread functions work
thread::yield_now();
thread::sleep(Duration::from_millis(100));
let current = thread::current();

// Builder pattern supported
let handle = thread::Builder::new()
    .name("worker".to_string())
    .stack_size(32 * 1024)
    .spawn(|| { /* ... */ })
    .unwrap();

// Join works the same way
let result = handle.join().unwrap();
assert_eq!(result, 42);

It automatically registers thread spawn/exit events for deadlock detection, visualization, and debugging purposes.

Deloxide::Mutex

A drop-in replacement for parking_lot::Mutex. It is also a direct alternative to std::sync::Mutex, but without lock poisoning (removing the need for .unwrap() on lock acquisition):

pub struct Mutex<T> {
    id: LockId,
    inner: ParkingLotMutex<T>,
    creator_thread_id: ThreadId,
}

impl<T> Mutex<T> {
    pub fn new(data: T) -> Self;
    pub fn lock(&self) -> MutexGuard<'_, T>;
    pub fn try_lock(&self) -> Option<MutexGuard<'_, T>>;
    pub fn into_inner(self) -> T where T: Sized;
    pub fn get_mut(&mut self) -> &mut T;
    pub fn id(&self) -> LockId;
    pub fn creator_thread_id(&self) -> ThreadId;
}

impl<T: Default> Default for Mutex<T> { /* ... */ }
impl<T> From<T> for Mutex<T> { /* ... */ }

All std::sync::Mutex methods are supported (except poisoning-related ones, as parking_lot doesn't use poisoning).

Deloxide::RwLock

A drop-in replacement for parking_lot::RwLock. It is also a direct alternative to std::sync::RwLock, but without lock poisoning:

pub struct RwLock<T> {
    id: LockId,
    inner: ParkingLotRwLock<T>,
    creator_thread_id: ThreadId,
}

impl<T> RwLock<T> {
    pub fn new(data: T) -> Self;
    pub fn read(&self) -> RwLockReadGuard<'_, T>;
    pub fn write(&self) -> RwLockWriteGuard<'_, T>;
    pub fn try_read(&self) -> Option<RwLockReadGuard<'_, T>>;
    pub fn try_write(&self) -> Option<RwLockWriteGuard<'_, T>>;
    pub fn into_inner(self) -> T where T: Sized;
    pub fn get_mut(&mut self) -> &mut T;
    pub fn id(&self) -> LockId;
    pub fn creator_thread_id(&self) -> ThreadId;
}

impl<T: Default> Default for RwLock<T> { /* ... */ }
impl<T> From<T> for RwLock<T> { /* ... */ }

All std::sync::RwLock methods are supported (except poisoning-related ones).

Deloxide::Condvar

A drop-in replacement for parking_lot::Condvar. It serves as a replacement for std::sync::Condvar but interacts with Deloxide::Mutex.

pub struct Condvar {
    id: CondvarId,
    inner: ParkingLotCondvar,
}

impl Condvar {
    pub fn new() -> Self;
    pub fn wait<T>(&self, guard: &mut MutexGuard<'_, T>);
    pub fn wait_while<T, F>(&self, guard: &mut MutexGuard<'_, T>, condition: F)
        where F: FnMut(&mut T) -> bool;
    pub fn wait_timeout<T>(&self, guard: &mut MutexGuard<'_, T>, timeout: Duration) -> bool;
    pub fn wait_timeout_while<T, F>(&self, guard: &mut MutexGuard<'_, T>, 
        timeout: Duration, condition: F) -> bool
        where F: FnMut(&mut T) -> bool;
    pub fn notify_one(&self);
    pub fn notify_all(&self);
    pub fn id(&self) -> CondvarId;
}

impl Default for Condvar { /* ... */ }

All std::sync::Condvar methods are supported.

Complete Usage Example

Here's a comprehensive example demonstrating all Deloxide primitives in a single scenario:

use deloxide::{Deloxide, Mutex, RwLock, Condvar, thread};
use std::sync::Arc;
use std::time::Duration;

fn main() {
    // Initialize the detector with logging and visualization
    // (requires the `logging-and-visualization` feature)
    // (Logging is enabled by default to "deloxide.log" if the feature is active)
    Deloxide::new()
        .callback(|info| {
            eprintln!("Deadlock detected! Threads: {:?}", info.thread_cycle);
            deloxide::showcase_this().expect("Failed to launch visualization");
        })
        .start()
        .expect("Failed to initialize detector");

    // Create synchronization primitives
    let counter = Arc::new(Mutex::new(0));
    let shared_data = Arc::new(RwLock::new(vec![1, 2, 3, 4, 5]));
    let condition_pair = Arc::new((Mutex::new(false), Condvar::new()));

    // Example 1: Mutex operations with potential deadlock
    let counter_clone1 = Arc::clone(&counter);
    let counter_clone2 = Arc::clone(&counter);
    let mutex_b = Arc::new(Mutex::new("Resource B"));
    let mutex_b_clone = Arc::clone(&mutex_b);

    // Thread 1: Lock counter, then mutex_b (deadlock scenario)
    thread::spawn(move || {
        let _count = counter_clone1.lock();
        thread::sleep(Duration::from_millis(100));
        let _b = mutex_b.lock();
    });

    // Thread 2: Lock mutex_b, then counter (deadlock scenario) 
    thread::spawn(move || {
        let _b = mutex_b_clone.lock();
        thread::sleep(Duration::from_millis(100));
        let _count = counter_clone2.lock();
    });

    // Example 2: RwLock with multiple readers and upgrade deadlock
    let shared_clone1 = Arc::clone(&shared_data);
    let shared_clone2 = Arc::clone(&shared_data);

    // Multiple reader threads
    for i in 0..3 {
        let shared_clone = Arc::clone(&shared_data);
        thread::spawn(move || {
            let data = shared_clone.read();
            println!("Reader {}: {:?}", i, *data);
            thread::sleep(Duration::from_millis(50));
        });
    }

    // Writer thread attempting upgrade (potential deadlock)
    thread::spawn(move || {
        let _read_guard = shared_clone1.read();
        println!("Writer acquired read lock, attempting upgrade...");
        thread::sleep(Duration::from_millis(25));
        let _write_guard = shared_clone2.write(); // This will deadlock!
        println!("Writer acquired write lock");
    });

    // Example 3: Condvar usage with wait_while
    let pair_clone = Arc::clone(&condition_pair);
    
    // Waiter thread using convenient wait_while method
    thread::spawn(move || {
        let (mutex, condvar) = (&pair_clone.0, &pair_clone.1);
        let mut ready = mutex.lock();
        // wait_while is more convenient than a manual loop!
        condvar.wait_while(&mut ready, |ready| !*ready);
        println!("Condition met, thread proceeding");
    });

    // Notifier thread
    let pair_clone2 = Arc::clone(&condition_pair);
    thread::spawn(move || {
        thread::sleep(Duration::from_millis(200));
        let (mutex, condvar) = (&pair_clone2.0, &pair_clone2.1);
        let mut ready = mutex.lock();
        *ready = true;
        condvar.notify_one();
        println!("Condition signaled");
    });

    // Let threads run and potentially detect deadlocks
    thread::sleep(Duration::from_secs(2));
    println!("Program completed");
}

C

The C API provides a complete interface to Deloxide through include/deloxide.h. It uses opaque pointers and helper macros to simplify integration with existing C codebases.

Core C API Functions

// Initialization
int deloxide_init(const char* log_path, void (*callback)(const char* json_info));
int deloxide_is_deadlock_detected();
void deloxide_reset_deadlock_flag();
int deloxide_is_logging_enabled();

// Mutex operations
void* deloxide_create_mutex(void);
void* deloxide_create_mutex_with_creator(uintptr_t creator_thread_id);
void deloxide_destroy_mutex(void* mutex);
int deloxide_lock_mutex(void* mutex);
int deloxide_unlock_mutex(void* mutex);
uintptr_t deloxide_get_mutex_creator(void* mutex);

// RwLock operations  
void* deloxide_create_rwlock(void);
void* deloxide_create_rwlock_with_creator(uintptr_t creator_thread_id);
void deloxide_destroy_rwlock(void* rwlock);
int deloxide_rw_lock_read(void* rwlock);
int deloxide_rw_unlock_read(void* rwlock);
int deloxide_rw_lock_write(void* rwlock);
int deloxide_rw_unlock_write(void* rwlock);
uintptr_t deloxide_get_rwlock_creator(void* rwlock);

// Condvar operations
void* deloxide_create_condvar(void);
void* deloxide_create_condvar_with_creator(uintptr_t creator_thread_id);
void deloxide_destroy_condvar(void* condvar);
int deloxide_condvar_wait(void* condvar, void* mutex);
int deloxide_condvar_wait_timeout(void* condvar, void* mutex, unsigned long timeout_ms);
int deloxide_condvar_notify_one(void* condvar);
int deloxide_condvar_notify_all(void* condvar);

// Thread tracking
int deloxide_register_thread_spawn(uintptr_t thread_id, uintptr_t parent_id);
int deloxide_register_thread_exit(uintptr_t thread_id);
uintptr_t deloxide_get_thread_id();

// Logging and visualization
int deloxide_flush_logs();
int deloxide_showcase(const char* log_path);
int deloxide_showcase_current();

// Stress Testing (requires "stress-test" feature)
int deloxide_enable_random_stress(double probability, unsigned long min_delay_us, unsigned long max_delay_us);
int deloxide_enable_component_stress(unsigned long min_delay_us, unsigned long max_delay_us);
int deloxide_disable_stress();

Helper Macros

Deloxide provides convenient macros for easier usage:

// Thread tracking macros
DEFINE_TRACKED_THREAD(fn_name)     // Define a tracked thread wrapper
CREATE_TRACKED_THREAD(thread, fn, arg)  // Create and start tracked thread

// Mutex macros
LOCK_MUTEX(mutex)                  // Lock with automatic tracking
UNLOCK_MUTEX(mutex)                // Unlock with automatic tracking

// RwLock macros
RWLOCK_READ(rwlock)                // Acquire read lock
RWLOCK_WRITE(rwlock)               // Acquire write lock  
RWUNLOCK_READ(rwlock)              // Release read lock
RWUNLOCK_WRITE(rwlock)             // Release write lock

// Condvar macros
CONDVAR_WAIT(condvar, mutex)       // Wait on condition variable
CONDVAR_NOTIFY_ONE(condvar)        // Signal one waiting thread
CONDVAR_NOTIFY_ALL(condvar)        // Signal all waiting threads

Complete C Usage Example

Here's a comprehensive example demonstrating all C API features in one program:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include "deloxide.h"

// Global synchronization primitives
void* counter_mutex;
void* shared_rwlock;
void* condition_mutex;
void* condition_var;
int shared_counter = 0;
int condition_ready = 0;

void deadlock_callback(const char* json_info) {
    printf("=== DEADLOCK DETECTED ===\n%s\n", json_info);
    deloxide_showcase_current();
}

// Example 1: Mutex deadlock scenario
void* mutex_worker1(void* arg) {
    void** mutexes = (void**)arg;
    void* mutex_a = mutexes[0];
    void* mutex_b = mutexes[1];
    
    printf("Thread 1: Locking mutex A\n");
    LOCK_MUTEX(mutex_a);
    usleep(100000);  // 100ms delay
    
    printf("Thread 1: Trying to lock mutex B\n");
    LOCK_MUTEX(mutex_b);  // Potential deadlock here
    
    printf("Thread 1: Got both locks, doing work\n");
    UNLOCK_MUTEX(mutex_b);
    UNLOCK_MUTEX(mutex_a);
    return NULL;
}

void* mutex_worker2(void* arg) {
    void** mutexes = (void**)arg;
    void* mutex_a = mutexes[0];
    void* mutex_b = mutexes[1];
    
    printf("Thread 2: Locking mutex B\n");
    LOCK_MUTEX(mutex_b);
    usleep(100000);  // 100ms delay
    
    printf("Thread 2: Trying to lock mutex A\n");
    LOCK_MUTEX(mutex_a);  // Potential deadlock here
    
    printf("Thread 2: Got both locks, doing work\n");
    UNLOCK_MUTEX(mutex_a);
    UNLOCK_MUTEX(mutex_b);
    return NULL;
}

// Example 2: RwLock usage
void* reader_worker(void* arg) {
    int reader_id = *(int*)arg;
    
    printf("Reader %d: Acquiring read lock\n", reader_id);
    RWLOCK_READ(shared_rwlock);
    
    printf("Reader %d: Reading shared data: %d\n", reader_id, shared_counter);
    usleep(50000);  // 50ms
    
    RWUNLOCK_READ(shared_rwlock);
    printf("Reader %d: Released read lock\n", reader_id);
    return NULL;
}

void* writer_worker(void* arg) {
    printf("Writer: Acquiring read lock first\n");
    RWLOCK_READ(shared_rwlock);
    
    printf("Writer: Attempting to upgrade to write lock\n");
    usleep(25000);  // 25ms
    RWLOCK_WRITE(shared_rwlock);  // This will deadlock!
    
    printf("Writer: Writing to shared data\n");
    shared_counter++;
    
    RWUNLOCK_WRITE(shared_rwlock);
    return NULL;
}

// Example 3: Condvar usage
void* condvar_waiter(void* arg) {
    printf("Waiter: Waiting for condition\n");
    LOCK_MUTEX(condition_mutex);
    
    while (!condition_ready) {
        CONDVAR_WAIT(condition_var, condition_mutex);
    }
    
    printf("Waiter: Condition met, proceeding\n");
    UNLOCK_MUTEX(condition_mutex);
    return NULL;
}

void* condvar_notifier(void* arg) {
    usleep(200000);  // 200ms delay
    
    printf("Notifier: Setting condition and signaling\n");
    LOCK_MUTEX(condition_mutex);
    condition_ready = 1;
    CONDVAR_NOTIFY_ONE(condition_var);
    UNLOCK_MUTEX(condition_mutex);
    return NULL;
}

// Define tracked thread wrappers
DEFINE_TRACKED_THREAD(mutex_worker1)
DEFINE_TRACKED_THREAD(mutex_worker2)
DEFINE_TRACKED_THREAD(reader_worker)
DEFINE_TRACKED_THREAD(writer_worker)
DEFINE_TRACKED_THREAD(condvar_waiter)
DEFINE_TRACKED_THREAD(condvar_notifier)

int main() {
    printf("Initializing Deloxide with deadlock detection\n");
    deloxide_init("c_deadlock_test.json", deadlock_callback);
    
    // Create synchronization primitives
    void* mutex_a = deloxide_create_mutex();
    void* mutex_b = deloxide_create_mutex();
    counter_mutex = deloxide_create_mutex();
    shared_rwlock = deloxide_create_rwlock();
    condition_mutex = deloxide_create_mutex();
    condition_var = deloxide_create_condvar();
    
    // Example 1: Mutex deadlock test
    printf("\n=== Testing Mutex Deadlock Scenario ===\n");
    void* mutex_args1[2] = {mutex_a, mutex_b};
    void* mutex_args2[2] = {mutex_a, mutex_b};
    
    pthread_t mutex_threads[2];
    CREATE_TRACKED_THREAD(mutex_threads[0], mutex_worker1, mutex_args1);
    CREATE_TRACKED_THREAD(mutex_threads[1], mutex_worker2, mutex_args2);
    
    // Example 2: RwLock upgrade deadlock test
    printf("\n=== Testing RwLock Upgrade Deadlock ===\n");
    pthread_t reader_threads[3];
    int reader_ids[3] = {1, 2, 3};
    
    for (int i = 0; i < 3; i++) {
        CREATE_TRACKED_THREAD(reader_threads[i], reader_worker, &reader_ids[i]);
    }
    
    pthread_t writer_thread;
    CREATE_TRACKED_THREAD(writer_thread, writer_worker, NULL);
    
    // Example 3: Condvar test (should work without deadlock)
    printf("\n=== Testing Condvar Synchronization ===\n");
    pthread_t condvar_threads[2];
    CREATE_TRACKED_THREAD(condvar_threads[0], condvar_waiter, NULL);
    CREATE_TRACKED_THREAD(condvar_threads[1], condvar_notifier, NULL);
    
    // Let all threads run and potentially detect deadlocks
    printf("\nWaiting for threads to complete or deadlock...\n");
    sleep(3);
    
    printf("Program completed\n");
    return 0;
}

Visualization

Deloxide includes a web-based visualization tool. After detecting a deadlock, use the showcase feature to view it in your browser:

// In Rust
deloxide::showcase("deadlock_log.log").expect("Failed to launch visualization");

// Or for the currently active log
deloxide::showcase_this().expect("Failed to launch visualization");

// In C
deloxide_showcase("deadlock_log.log");

// Or for the currently active log
deloxide_showcase_current();

You can also automatically launch the visualization when a deadlock is detected by calling the showcase function in your deadlock callback.

Additionally, you can manually upload a log file to visualize deadlocks through the web interface:

Deloxide Showcase

Project Architecture

How Deloxide Works

1. Initialization: The application initializes Deloxide. Logging and lock order checking are enabled by default if their respective features are active.

2. Resource Creation: When threads, mutexes, and reader-writer locks are created, they're registered with the deadlock detector.

3. Lock Operations: When a thread attempts to acquire a lock:

   • Optimistic Fast Path: The system first attempts a fast-path acquisition using atomic operations. If successful (uncontended), it bypasses the detector entirely (zero overhead).
   • Slow Path (Contended): If the lock is held, the attempt is recorded by the detector.
   • A "wait-for" edge is added to the graph.
   • The detector checks for cycles in the "wait-for" graph.
   • If a cycle is found, a deadlock is reported.

4. Deadlock Detection: When a deadlock is detected, the callback is invoked with detailed information, including which threads are involved and which locks they're waiting for.

5. Visualization: The showcase function can be called (automatically in the callback or manually) to visualize the thread-lock interactions in a web browser.

Core Components

1. Dual Detection Engine
   • Wait-For Graph (WFG): The default, reactive tier. Detects active circular dependencies with mathematical certainty (0 false positives).
   • Lock Order Graph (LOG): An optional, proactive tier. Analyzes historical acquisition patterns to warn about potential deadlocks before they occur (requires lock-order-graph feature).

2. Optimistic Fast Path

   • Implements an "Optimistic Fast Path" architecture using atomic release-acquire semantics.
   • Bypasses the global detector entirely for uncontended locks.
   • Lowers instrumentation overhead to just ~10.8ns (1.09x of standard parking_lot), enabling "always-on" production monitoring.

3. Stress Testing Framework (Optional)

   • Employs Probabilistic Concurrency Testing (PCT) to expose Heisenbugs.
   • Component-Based Targeting: Intelligently injects delays into interacting lock groups.
   • Achieves a 99.5% manifestation rate for latent deadlocks (vs 63.4% for passive tools).

4. Resource Tracking

   • Tracks threads and locks as resources with lifecycles
   • Manages parent-child relationships between threads
   • Automatically cleans up resources when threads exit

5. Visualization Pipeline

   • Serverless Sharing: Compresses logs into URL-safe Base64 payloads (MessagePack + Gzip).
   • Privacy-First: All decoding and rendering happens client-side; no data is sent to external servers.
   • Provides interactive timelines and dependency graphs.
   

6. Cross-Language Support

   • Rust API with Mutex, RwLock, Condvar, and thread module
   • C API through FFI bindings in deloxide.h
   • Simple macros for C to handle common operations

Lock Order Graph

Deloxide includes an optional lock order graph feature that detects potential deadlocks by tracking lock acquisition ordering patterns, even when threads don't actually block. This provides early warning of dangerous lock ordering patterns that could lead to deadlocks.

Enabling Lock Order Graph

In Rust:

Enable the feature in your Cargo.toml:

[dependencies]
deloxide = { version = "1.0", features = ["lock-order-graph"] }

Then use the lock order checking API:

use deloxide::{Deloxide, DeadlockSource};

Deloxide::new()
    .with_log("deadlock.log")
    // Lock order checking is enabled by default if the feature is on,
    // but you can explicitly enable it (no-op) or disable it with .no_lock_order_checking()
    .callback(|info| {
        match info.source {
            DeadlockSource::WaitForGraph => {
                eprintln!("🚨 ACTUAL DEADLOCK! Threads are blocked.");
            }
            DeadlockSource::LockOrderViolation => {
                eprintln!("⚠️  SUSPECTED DEADLOCK! Dangerous lock ordering pattern.");
                if let Some(cycle) = &info.lock_order_cycle {
                    eprintln!("Lock order cycle: {:?}", cycle);
                }
            }
        }
    })
    .start()
    .expect("Failed to initialize detector");

How Lock Order Graph Works

When a thread holds lock A and then acquires lock B, the system records that A < B (A must be acquired before B). If later the system sees an attempt to acquire A while holding B (B < A), this creates a cycle in the lock order graph and indicates a potential deadlock.

Note: Lock order graph detection may report patterns that never actually deadlock (false positives). It's recommended for development and testing, not production.

Stress Testing

Deloxide includes an optional stress testing feature to increase the probability of deadlock manifestation during testing. This feature helps expose potential deadlocks by strategically delaying threads at critical points.

Enabling Stress Testing

In Rust:

Enable the feature in your Cargo.toml:

[dependencies]
deloxide = { version = "1.0", features = ["stress-test"] }

Then use the stress testing API:

// With random preemption strategy
Deloxide::new()
    .with_log("deadlock.log")
    .with_random_stress()
    .callback(|info| {
        eprintln!("Deadlock detected! Cycle: {:?}", info.thread_cycle);
    })
    .start()
    .expect("Failed to initialize detector");

// Or with component-based strategy and custom configuration
use deloxide::StressConfig;

Deloxide::new()
    .with_log("deadlock.log")
    .with_component_stress()
    .with_stress_config(StressConfig {
        preemption_probability: 0.8,
        min_delay_us: 500,
        max_delay_us: 2000,
        preempt_after_release: true,
    })
    .start()
    .expect("Failed to initialize detector");

// Or use one of the presets
Deloxide::new()
    .with_log("deadlock.log")
    .with_component_stress()
    .with_stress_config(StressConfig::aggressive())
    .start()
    .expect("Failed to initialize detector");

In C:

Build Deloxide with the stress-test feature enabled, then:

// Enable random preemption stress testing (70% probability, 100-1000us delays)
deloxide_enable_random_stress(0.7, 100, 1000);

// Or enable component-based stress testing
deloxide_enable_component_stress(5000, 15000);

// Initialize detector
deloxide_init("deadlock.log", deadlock_callback);

Stress Testing Modes

• Random Preemption: Randomly delays threads before lock acquisitions with configurable probability
• Component-Based: Analyzes lock acquisition patterns and intelligently targets delays to increase deadlock probability

Comparison with Other Solutions

The Rust ecosystem offers several approaches to concurrency safety, each with distinct trade-offs. Deloxide focuses on bridging the gap between "safe but slow" debugging tools and "fast but unsafe" production primitives.

The Landscape

• Static Analysis: Tools that check code at compile time. They often suffer from high false positive rates (flagging safe code as dangerous), making them noisy for complex projects.
• Passive Dynamic Detection (parking_lot): Monitors locks asynchronously. While fast, it can miss "Heisenbugs" (transient deadlocks) because it doesn't force thread interleavings, and it reports deadlocks only after a delay (polling).
• Synchronous Graph Analysis (no_deadlocks): Checks for cycles on every lock operation. This guarantees detection but incurs prohibitive overhead (>1000x), making it unusable for real-time applications.

When to use what?

• Use parking_lot (without detection): If pure raw performance is the absolute only metric that matters, and you have mathematically proven your system cannot deadlock (e.g., essentially lock-free designs). It avoids the ~1ns atomic overhead of Deloxide's fast path.
• Use deloxide: For everything else.
  • Development: Instant feedback and visualization.
  • Testing: Stress testing to find Heisenbugs.
  • Production: The "Optimistic Fast Path" means you get safety netting with negligible cost (and sometimes speedups in high contention).

Performance & Validation

Deloxide has been evaluated through a three-tiered testing framework: Correctness (Guaranteed Deadlocks), Stress Testing (Heisenbugs), and Performance (Micro/Macrobenchmarks).

1. Methodology

• Guaranteed Deadlock Tests: Validates that the WFG logic detects 100% of deterministic cycles (e.g., barriers enforcing circular wait).
• Heisenbug Manifestation: Uses probabilistic scheduling to force race conditions in non-deterministic scenarios (e.g., Dining Philosophers without barriers).
• False Positive Analysis: Tested against 9 complex "false positive" scenarios (e.g., Gate Guarded, Lock Order Inversion) to ensure 0% false alarm rate.

2. Microbenchmark Overhead

The "Optimistic Fast Path" ensures minimal impact on atomic operations. Deloxide incurs only ~1ns overhead per lock operation.

Metric	STD	PL+DD	DX	DX (LOG)	DX (COMP)	ND
Mutex Lock	8.7ns	9.9ns	10.8ns	58.1ns	229.4ns	10,527ns
RwLock Write	10.1ns	12.8ns	13.9ns	57.7ns	234.1ns	10,797ns
RwLock Read	13.9ns	16.1ns	62.4ns	85.5ns	222.5ns	10,895ns
Condvar	17.1µs	17.2µs	19.6µs	17.4µs	20.3µs	2,100µs

PL+DD = parking_lot + detection, ND = no_deadlocks. DX (COMP) intentional overhead forces thread interleaving.

3. Real-World Validation: Ray Tracing

To rigorously evaluate overhead in a realistic high-performance context, we architected a custom path-tracing renderer in Rust. Unlike data-parallel approaches (like Rayon) that isolate memory, this implementation uses a shared framebuffer architecture with a fine-grained tile-based locking strategy (16x16 pixel chunks).

• Workload: High-complexity scene with multiple material types and max recursion depth of 50 bounces.
• Contention: At 1080p resolution, workers contend for locks over 129,600 times per frame (~4kHz locking frequency).
• Result: This specifically targets the "worst-case" scenario for a deadlock detector: high-frequency, fine-grained locking.

In this saturation test, Deloxide demonstrated superior deterministic stability.

Config	426x240	854x480	1280x720	1920x1080 (Saturation)
STD	0.81s ± 0.03	3.41s ± 0.15	7.33s ± 0.31	17.22s ± 0.65
PL+DD	0.81s ± 0.00	3.26s ± 0.02	7.19s ± 0.03	18.32s ± 0.06
DX (Default)	0.80s ± 0.00	3.18s ± 0.01	7.09s ± 0.03	16.67s ± 0.09
ND	33.0s ± 31.4	220.9s ± 182	192.9s ± 281	329.1s ± 554

Key Result: At 1080p, Deloxide (16.67s) is 9% faster than the baseline parking_lot (18.32s) and significantly more stable (CV < 0.6%) than STD.

Clarification: Deloxide outperforms the baseline not because detection makes it faster, but because our underlying mutex implementation handles high-contention tail latency better than the OS primitive.

4. Heisenbug Manifestation Rates (Stress Testing)

Comparison of manifestation rates (1000 iterations) across different strategies. Active stress testing is required to find latent bugs.

Scenario	DX (Passive)	DX (RAND)	DX (AGG)	DX (COMP)	PL+DD	ND
dining_philosophers	40.3%	65.4%	83.6%	98.7%	54.1%	75.5%
five_lock_cycle	100.0%	100.0%	100.0%	100.0%	100.0%	99.4%
rwlock_deadlock	41.5%	71.1%	88.1%	100.0%	60.4%	100.0%
three_lock_cycle	88.7%	98.7%	99.4%	100.0%	77.4%	98.7%
two_lock	17.6%	57.2%	81.8%	98.7%	25.2%	73.6%
Average Rate	57.6%	78.5%	90.6%	99.5%	63.4%	89.4%

5. False Positive Analysis

Deloxide (WFG) achieved 0 False Positives, utilizing a mathematically rigorous cycle detection algorithm.

• Tested Patterns: Gate Guarded, Lock-Free Intervals, Lock Order Inversion, Thread-Local Hierarchies.
• Result: Perfect specificity.

Feature Matrix

Feature	STD	PL+DD	ND	DX
Mutex Overhead	0.88x	1.00x	1063.33x	1.09x
Ray Tracing (1080p)	0.94x	1.00x	17.96x	0.91x (Faster)
Detection Method	None	Async (Poll)	Synchronous	Synchronous (Instant)
Lock Order Analysis	No	No	No	Yes
Stress Testing	No	No	No	Yes
Visualization	No	No	Text Dump	Interactive URL
False Positive Rate	N/A	Zero	Zero	Zero (WFG)

STD = std::sync, PL+DD = parking_lot with deadlock_detection, ND = no_deadlocks, DX = Deloxide

Documentation

For more detailed documentation:

• Crates.io: https://crates.io/crates/deloxide
• Rust Docs: https://docs.rs/deloxide
• C API: See include/deloxide.h and https://docs.rs/deloxide/latest/deloxide/ffi/index.html

License

Deloxide is licensed under the terms of the MIT license, the Apache License (Version 2.0), or the Coffeeware License, at your option.

Option 1: The "Serious" Licenses

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Option 2: The "Fun" License

/*
 *      ( (
 *       ) )
 *    ........
 *    |      |]  ☕
 *    \      /
 *     `----'
 *
 * "THE COFFEEWARE LICENSE" (Revision 1, Deloxide Edition):
 * (Inspired by the original Beerware License by Poul-Henning Kamp)
 *
 * Emirhan Tala and Ulaş Can Demirbağ wrote this file. As long as you retain
 * this notice, you can do whatever you want with this stuff — run it, fork it,
 * deploy it, tattoo it, or summon it in a thread ritual. We don't care.
 *
 * Just remember: we make no guarantees, provide no warranties, and accept no
 * responsibility for anything that happens. This software may or may not work,
 * may or may not cause your system to spontaneously combust into deadlocks,
 * and may or may not summon a sentient debugger from the void. But we accept
 * coffee! If we ever meet someday and you think this code helped you can buy 
 * us a coffee in return. Or not. No pressure. But coffee is nice. We love it!
 * ----------------------------------------------------------------------------
 */