Struct Mutex 

pub struct Mutex<T>
where
    T: ?Sized,
{ /* private fields */ }

A mutual exclusion primitive useful for protecting shared data

This mutex will block threads waiting for the lock to become available. The mutex can be created via a new constructor. Each mutex has a type parameter which represents the data that it is protecting. The data can only be accessed through the RAII guards returned from lock and try_lock, which guarantees that the data is only ever accessed when the mutex is locked.

Poisoning

The mutexes in this module implement a strategy called “poisoning” where a mutex becomes poisoned if it recognizes that the thread holding it has panicked.

Once a mutex is poisoned, all other threads are unable to access the data by default as it is likely tainted (some invariant is not being upheld). For a mutex, this means that the lock and try_lock methods return a Result which indicates whether a mutex has been poisoned or not. Most usage of a mutex will simply unwrap() these results, propagating panics among threads to ensure that a possibly invalid invariant is not witnessed.

Poisoning is only advisory: the PoisonError type has an into_inner method which will return the guard that would have otherwise been returned on a successful lock. This allows access to the data, despite the lock being poisoned.

In addition, the panic detection is not ideal, so even unpoisoned mutexes need to be handled with care, since certain panics may have been skipped. Here is a non-exhaustive list of situations where this might occur:

• If a mutex is locked while a panic is underway, e.g. within a Drop implementation or a panic hook, panicking for the second time while the lock is held will leave the mutex unpoisoned. Note that while double panic usually aborts the program, catch_unwind can prevent this.

• Locking and unlocking the mutex across different panic contexts, e.g. by storing the guard to a Cell within Drop::drop and accessing it outside, or vice versa, can affect poisoning status in an unexpected way.

• Foreign exceptions do not currently trigger poisoning even in absence of other panics.

While this rarely happens in realistic code, unsafe code cannot rely on poisoning for soundness, since the behavior of poisoning can depend on outside context. Here’s an example of incorrect use of poisoning:

use std::sync::Mutex;

struct MutexBox<T> {
    data: Mutex<*mut T>,
}

impl<T> MutexBox<T> {
    pub fn new(value: T) -> Self {
        Self {
            data: Mutex::new(Box::into_raw(Box::new(value))),
        }
    }

    pub fn replace_with(&self, f: impl FnOnce(T) -> T) {
        let ptr = self.data.lock().expect("poisoned");
        // While `f` is running, the data is moved out of `*ptr`. If `f`
        // panics, `*ptr` keeps pointing at a dropped value. The intention
        // is that this will poison the mutex, so the following calls to
        // `replace_with` will panic without reading `*ptr`. But since
        // poisoning is not guaranteed to occur if this is run from a panic
        // hook, this can lead to use-after-free.
        unsafe {
            (*ptr).write(f((*ptr).read()));
        }
    }
}

Examples

use std::sync::{Arc, Mutex};
use std::thread;
use std::sync::mpsc::channel;

const N: usize = 10;

// Spawn a few threads to increment a shared variable (non-atomically), and
// let the main thread know once all increments are done.
//
// Here we're using an Arc to share memory among threads, and the data inside
// the Arc is protected with a mutex.
let data = Arc::new(Mutex::new(0));

let (tx, rx) = channel();
for _ in 0..N {
    let (data, tx) = (Arc::clone(&data), tx.clone());
    thread::spawn(move || {
        // The shared state can only be accessed once the lock is held.
        // Our non-atomic increment is safe because we're the only thread
        // which can access the shared state when the lock is held.
        //
        // We unwrap() the return value to assert that we are not expecting
        // threads to ever fail while holding the lock.
        let mut data = data.lock().unwrap();
        *data += 1;
        if *data == N {
            tx.send(()).unwrap();
        }
        // the lock is unlocked here when `data` goes out of scope.
    });
}

rx.recv().unwrap();

To recover from a poisoned mutex:

use std::sync::{Arc, Mutex};
use std::thread;

let lock = Arc::new(Mutex::new(0_u32));
let lock2 = Arc::clone(&lock);

let _ = thread::spawn(move || -> () {
    // This thread will acquire the mutex first, unwrapping the result of
    // `lock` because the lock has not been poisoned.
    let _guard = lock2.lock().unwrap();

    // This panic while holding the lock (`_guard` is in scope) will poison
    // the mutex.
    panic!();
}).join();

// The lock is poisoned by this point, but the returned result can be
// pattern matched on to return the underlying guard on both branches.
let mut guard = match lock.lock() {
    Ok(guard) => guard,
    Err(poisoned) => poisoned.into_inner(),
};

*guard += 1;

To unlock a mutex guard sooner than the end of the enclosing scope, either create an inner scope or drop the guard manually.

use std::sync::{Arc, Mutex};
use std::thread;

const N: usize = 3;

let data_mutex = Arc::new(Mutex::new(vec![1, 2, 3, 4]));
let res_mutex = Arc::new(Mutex::new(0));

let mut threads = Vec::with_capacity(N);
(0..N).for_each(|_| {
    let data_mutex_clone = Arc::clone(&data_mutex);
    let res_mutex_clone = Arc::clone(&res_mutex);

    threads.push(thread::spawn(move || {
        // Here we use a block to limit the lifetime of the lock guard.
        let result = {
            let mut data = data_mutex_clone.lock().unwrap();
            // This is the result of some important and long-ish work.
            let result = data.iter().fold(0, |acc, x| acc + x * 2);
            data.push(result);
            result
            // The mutex guard gets dropped here, together with any other values
            // created in the critical section.
        };
        // The guard created here is a temporary dropped at the end of the statement, i.e.
        // the lock would not remain being held even if the thread did some additional work.
        *res_mutex_clone.lock().unwrap() += result;
    }));
});

let mut data = data_mutex.lock().unwrap();
// This is the result of some important and long-ish work.
let result = data.iter().fold(0, |acc, x| acc + x * 2);
data.push(result);
// We drop the `data` explicitly because it's not necessary anymore and the
// thread still has work to do. This allows other threads to start working on
// the data immediately, without waiting for the rest of the unrelated work
// to be done here.
//
// It's even more important here than in the threads because we `.join` the
// threads after that. If we had not dropped the mutex guard, a thread could
// be waiting forever for it, causing a deadlock.
// As in the threads, a block could have been used instead of calling the
// `drop` function.
drop(data);
// Here the mutex guard is not assigned to a variable and so, even if the
// scope does not end after this line, the mutex is still released: there is
// no deadlock.
*res_mutex.lock().unwrap() += result;

threads.into_iter().for_each(|thread| {
    thread
        .join()
        .expect("The thread creating or execution failed !")
});

assert_eq!(*res_mutex.lock().unwrap(), 800);

Implementations

impl<T> Mutex<T>

pub const fn new(t: T) -> Mutex<T>

Creates a new mutex in an unlocked state ready for use.

Examples

use std::sync::Mutex;

let mutex = Mutex::new(0);

Examples found in repository

examples/3d/occlusion_culling.rs (line 142)

    fn new() -> Self {
        Self(Arc::new(Mutex::new(None)))
    }

pub fn get_cloned(&self) -> Result<T, PoisonError<()>>

where T: Clone,

🔬This is a nightly-only experimental API. (lock_value_accessors)

Returns the contained value by cloning it.

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error instead.

Examples

#![feature(lock_value_accessors)]

use std::sync::Mutex;

let mut mutex = Mutex::new(7);

assert_eq!(mutex.get_cloned().unwrap(), 7);

pub fn set(&self, value: T) -> Result<(), PoisonError<T>>

🔬This is a nightly-only experimental API. (lock_value_accessors)

Sets the contained value.

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error containing the provided value instead.

Examples

#![feature(lock_value_accessors)]

use std::sync::Mutex;

let mut mutex = Mutex::new(7);

assert_eq!(mutex.get_cloned().unwrap(), 7);
mutex.set(11).unwrap();
assert_eq!(mutex.get_cloned().unwrap(), 11);

pub fn replace(&self, value: T) -> Result<T, PoisonError<T>>

🔬This is a nightly-only experimental API. (lock_value_accessors)

Replaces the contained value with value, and returns the old contained value.

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error containing the provided value instead.

Examples

#![feature(lock_value_accessors)]

use std::sync::Mutex;

let mut mutex = Mutex::new(7);

assert_eq!(mutex.replace(11).unwrap(), 7);
assert_eq!(mutex.get_cloned().unwrap(), 11);

impl<T> Mutex<T>

where T: ?Sized,

pub fn lock(&self) -> Result<MutexGuard<'_, T>, PoisonError<MutexGuard<'_, T>>>

Acquires a mutex, blocking the current thread until it is able to do so.

This function will block the local thread until it is available to acquire the mutex. Upon returning, the thread is the only thread with the lock held. An RAII guard is returned to allow scoped unlock of the lock. When the guard goes out of scope, the mutex will be unlocked.

The exact behavior on locking a mutex in the thread which already holds the lock is left unspecified. However, this function will not return on the second call (it might panic or deadlock, for example).

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error once the mutex is acquired. The acquired mutex guard will be contained in the returned error.

Panics

This function might panic when called if the lock is already held by the current thread.

Examples

use std::sync::{Arc, Mutex};
use std::thread;

let mutex = Arc::new(Mutex::new(0));
let c_mutex = Arc::clone(&mutex);

thread::spawn(move || {
    *c_mutex.lock().unwrap() = 10;
}).join().expect("thread::spawn failed");
assert_eq!(*mutex.lock().unwrap(), 10);

Examples found in repository

examples/3d/occlusion_culling.rs (line 151)

fn init_saved_indirect_parameters(
    render_device: Res<RenderDevice>,
    gpu_preprocessing_support: Res<GpuPreprocessingSupport>,
    saved_indirect_parameters: Res<SavedIndirectParameters>,
) {
    let mut saved_indirect_parameters = saved_indirect_parameters.0.lock().unwrap();
    *saved_indirect_parameters = Some(SavedIndirectParametersData {
        data: vec![],
        count: 0,
        occlusion_culling_supported: gpu_preprocessing_support.is_culling_supported(),
        // In order to determine how many meshes were culled, we look at the indirect count buffer
        // that Bevy only populates if the platform supports `multi_draw_indirect_count`. So, if we
        // don't have that feature, then we don't bother to display how many meshes were culled.
        occlusion_culling_introspection_supported: render_device
            .features()
            .contains(WgpuFeatures::MULTI_DRAW_INDIRECT_COUNT),
    });
}

/// The demo's current settings.
#[derive(Resource)]
struct AppStatus {
    /// Whether occlusion culling is presently enabled.
    ///
    /// By default, this is set to true.
    occlusion_culling: bool,
}

impl Default for AppStatus {
    fn default() -> Self {
        AppStatus {
            occlusion_culling: true,
        }
    }
}

fn main() {
    let render_debug_flags = RenderDebugFlags::ALLOW_COPIES_FROM_INDIRECT_PARAMETERS;

    App::new()
        .add_plugins(
            DefaultPlugins
                .set(WindowPlugin {
                    primary_window: Some(Window {
                        title: "Bevy Occlusion Culling Example".into(),
                        ..default()
                    }),
                    ..default()
                })
                .set(RenderPlugin {
                    debug_flags: render_debug_flags,
                    ..default()
                })
                .set(PbrPlugin {
                    debug_flags: render_debug_flags,
                    ..default()
                }),
        )
        .add_plugins(ReadbackIndirectParametersPlugin)
        .init_resource::<AppStatus>()
        .add_systems(Startup, setup)
        .add_systems(Update, spin_small_cubes)
        .add_systems(Update, spin_large_cube)
        .add_systems(Update, update_status_text)
        .add_systems(Update, toggle_occlusion_culling_on_request)
        .run();
}

impl Plugin for ReadbackIndirectParametersPlugin {
    fn build(&self, app: &mut App) {
        // Create the `SavedIndirectParameters` resource that we're going to use
        // to communicate between the thread that the GPU-to-CPU readback
        // callback runs on and the main application threads. This resource is
        // atomically reference counted. We store one reference to the
        // `SavedIndirectParameters` in the main app and another reference in
        // the render app.
        let saved_indirect_parameters = SavedIndirectParameters::new();
        app.insert_resource(saved_indirect_parameters.clone());

        // Fetch the render app.
        let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app
            // Insert another reference to the `SavedIndirectParameters`.
            .insert_resource(saved_indirect_parameters)
            // Setup the parameters in RenderStartup.
            .add_systems(RenderStartup, init_saved_indirect_parameters)
            .init_resource::<IndirectParametersStagingBuffers>()
            .add_systems(ExtractSchedule, readback_indirect_parameters)
            .add_systems(
                Render,
                create_indirect_parameters_staging_buffers
                    .in_set(RenderSystems::PrepareResourcesFlush),
            )
            // Add the node that allows us to read the indirect parameters back
            // from the GPU to the CPU, which allows us to determine how many
            // meshes were culled.
            .add_render_graph_node::<ReadbackIndirectParametersNode>(
                Core3d,
                ReadbackIndirectParameters,
            )
            // We read back the indirect parameters any time after
            // `EndMainPass`. Readback doesn't particularly need to execute
            // before `EndMainPassPostProcessing`, but we specify that anyway
            // because we want to make the indirect parameters run before
            // *something* in the graph, and `EndMainPassPostProcessing` is a
            // good a node as any other.
            .add_render_graph_edges(
                Core3d,
                (
                    Node3d::EndMainPass,
                    ReadbackIndirectParameters,
                    Node3d::EndMainPassPostProcessing,
                ),
            );
    }
}

/// Spawns all the objects in the scene.
fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    spawn_small_cubes(&mut commands, &mut meshes, &mut materials);
    spawn_large_cube(&mut commands, &asset_server, &mut meshes, &mut materials);
    spawn_light(&mut commands);
    spawn_camera(&mut commands);
    spawn_help_text(&mut commands);
}

/// Spawns the rotating sphere of small cubes.
fn spawn_small_cubes(
    commands: &mut Commands,
    meshes: &mut Assets<Mesh>,
    materials: &mut Assets<StandardMaterial>,
) {
    // Add the cube mesh.
    let small_cube = meshes.add(Cuboid::new(
        SMALL_CUBE_SIZE,
        SMALL_CUBE_SIZE,
        SMALL_CUBE_SIZE,
    ));

    // Add the cube material.
    let small_cube_material = materials.add(StandardMaterial {
        base_color: SILVER.into(),
        ..default()
    });

    // Create the entity that the small cubes will be parented to. This is the
    // entity that we rotate.
    let sphere_parent = commands
        .spawn(Transform::from_translation(Vec3::ZERO))
        .insert(Visibility::default())
        .insert(SphereParent)
        .id();

    // Now we have to figure out where to place the cubes. To do that, we create
    // a sphere mesh, but we don't add it to the scene. Instead, we inspect the
    // sphere mesh to find the positions of its vertices, and spawn a small cube
    // at each one. That way, we end up with a bunch of cubes arranged in a
    // spherical shape.

    // Create the sphere mesh, and extract the positions of its vertices.
    let sphere = Sphere::new(OUTER_RADIUS)
        .mesh()
        .ico(OUTER_SUBDIVISION_COUNT)
        .unwrap();
    let sphere_positions = sphere.attribute(Mesh::ATTRIBUTE_POSITION).unwrap();

    // At each vertex, create a small cube.
    for sphere_position in sphere_positions.as_float3().unwrap() {
        let sphere_position = Vec3::from_slice(sphere_position);
        let small_cube = commands
            .spawn(Mesh3d(small_cube.clone()))
            .insert(MeshMaterial3d(small_cube_material.clone()))
            .insert(Transform::from_translation(sphere_position))
            .id();
        commands.entity(sphere_parent).add_child(small_cube);
    }
}

/// Spawns the large cube at the center of the screen.
///
/// This cube rotates chaotically and occludes small cubes behind it.
fn spawn_large_cube(
    commands: &mut Commands,
    asset_server: &AssetServer,
    meshes: &mut Assets<Mesh>,
    materials: &mut Assets<StandardMaterial>,
) {
    commands
        .spawn(Mesh3d(meshes.add(Cuboid::new(
            LARGE_CUBE_SIZE,
            LARGE_CUBE_SIZE,
            LARGE_CUBE_SIZE,
        ))))
        .insert(MeshMaterial3d(materials.add(StandardMaterial {
            base_color: WHITE.into(),
            base_color_texture: Some(asset_server.load("branding/icon.png")),
            ..default()
        })))
        .insert(Transform::IDENTITY)
        .insert(LargeCube);
}

// Spins the outer sphere a bit every frame.
//
// This ensures that the set of cubes that are hidden and shown varies over
// time.
fn spin_small_cubes(mut sphere_parents: Query<&mut Transform, With<SphereParent>>) {
    for mut sphere_parent_transform in &mut sphere_parents {
        sphere_parent_transform.rotate_y(ROTATION_SPEED);
    }
}

/// Spins the large cube a bit every frame.
///
/// The chaotic rotation adds a bit of randomness to the scene to better
/// demonstrate the dynamicity of the occlusion culling.
fn spin_large_cube(mut large_cubes: Query<&mut Transform, With<LargeCube>>) {
    for mut transform in &mut large_cubes {
        transform.rotate(Quat::from_euler(
            EulerRot::XYZ,
            0.13 * ROTATION_SPEED,
            0.29 * ROTATION_SPEED,
            0.35 * ROTATION_SPEED,
        ));
    }
}

/// Spawns a directional light to illuminate the scene.
fn spawn_light(commands: &mut Commands) {
    commands
        .spawn(DirectionalLight::default())
        .insert(Transform::from_rotation(Quat::from_euler(
            EulerRot::ZYX,
            0.0,
            PI * -0.15,
            PI * -0.15,
        )));
}

/// Spawns a camera that includes the depth prepass and occlusion culling.
fn spawn_camera(commands: &mut Commands) {
    commands
        .spawn(Camera3d::default())
        .insert(Transform::from_xyz(0.0, 0.0, 9.0).looking_at(Vec3::ZERO, Vec3::Y))
        .insert(DepthPrepass)
        .insert(OcclusionCulling);
}

/// Spawns the help text at the upper left of the screen.
fn spawn_help_text(commands: &mut Commands) {
    commands.spawn((
        Text::new(""),
        Node {
            position_type: PositionType::Absolute,
            top: px(12),
            left: px(12),
            ..default()
        },
    ));
}

impl render_graph::Node for ReadbackIndirectParametersNode {
    fn run<'w>(
        &self,
        _: &mut RenderGraphContext,
        render_context: &mut RenderContext<'w>,
        world: &'w World,
    ) -> Result<(), NodeRunError> {
        // Extract the buffers that hold the GPU indirect draw parameters from
        // the world resources. We're going to read those buffers to determine
        // how many meshes were actually drawn.
        let (Some(indirect_parameters_buffers), Some(indirect_parameters_mapping_buffers)) = (
            world.get_resource::<IndirectParametersBuffers>(),
            world.get_resource::<IndirectParametersStagingBuffers>(),
        ) else {
            return Ok(());
        };

        // Get the indirect parameters buffers corresponding to the opaque 3D
        // phase, since all our meshes are in that phase.
        let Some(phase_indirect_parameters_buffers) =
            indirect_parameters_buffers.get(&TypeId::of::<Opaque3d>())
        else {
            return Ok(());
        };

        // Grab both the buffers we're copying from and the staging buffers
        // we're copying to. Remember that we can't map the indirect parameters
        // buffers directly, so we have to copy their contents to a staging
        // buffer.
        let (
            Some(indexed_data_buffer),
            Some(indexed_batch_sets_buffer),
            Some(indirect_parameters_staging_data_buffer),
            Some(indirect_parameters_staging_batch_sets_buffer),
        ) = (
            phase_indirect_parameters_buffers.indexed.data_buffer(),
            phase_indirect_parameters_buffers
                .indexed
                .batch_sets_buffer(),
            indirect_parameters_mapping_buffers.data.as_ref(),
            indirect_parameters_mapping_buffers.batch_sets.as_ref(),
        )
        else {
            return Ok(());
        };

        // Copy from the indirect parameters buffers to the staging buffers.
        render_context.command_encoder().copy_buffer_to_buffer(
            indexed_data_buffer,
            0,
            indirect_parameters_staging_data_buffer,
            0,
            indexed_data_buffer.size(),
        );
        render_context.command_encoder().copy_buffer_to_buffer(
            indexed_batch_sets_buffer,
            0,
            indirect_parameters_staging_batch_sets_buffer,
            0,
            indexed_batch_sets_buffer.size(),
        );

        Ok(())
    }
}

/// Creates the staging buffers that we use to read back the indirect parameters
/// from the GPU to the CPU.
///
/// We read the indirect parameters from the GPU to the CPU in order to display
/// the number of meshes that were culled each frame.
///
/// We need these staging buffers because `wgpu` doesn't allow us to read the
/// contents of the indirect parameters buffers directly. We must first copy
/// them from the GPU to a staging buffer, and then read the staging buffer.
fn create_indirect_parameters_staging_buffers(
    mut indirect_parameters_staging_buffers: ResMut<IndirectParametersStagingBuffers>,
    indirect_parameters_buffers: Res<IndirectParametersBuffers>,
    render_device: Res<RenderDevice>,
) {
    let Some(phase_indirect_parameters_buffers) =
        indirect_parameters_buffers.get(&TypeId::of::<Opaque3d>())
    else {
        return;
    };

    // Fetch the indirect parameters buffers that we're going to copy from.
    let (Some(indexed_data_buffer), Some(indexed_batch_set_buffer)) = (
        phase_indirect_parameters_buffers.indexed.data_buffer(),
        phase_indirect_parameters_buffers
            .indexed
            .batch_sets_buffer(),
    ) else {
        return;
    };

    // Build the staging buffers. Make sure they have the same sizes as the
    // buffers we're copying from.
    indirect_parameters_staging_buffers.data =
        Some(render_device.create_buffer(&BufferDescriptor {
            label: Some("indexed data staging buffer"),
            size: indexed_data_buffer.size(),
            usage: BufferUsages::MAP_READ | BufferUsages::COPY_DST,
            mapped_at_creation: false,
        }));
    indirect_parameters_staging_buffers.batch_sets =
        Some(render_device.create_buffer(&BufferDescriptor {
            label: Some("indexed batch set staging buffer"),
            size: indexed_batch_set_buffer.size(),
            usage: BufferUsages::MAP_READ | BufferUsages::COPY_DST,
            mapped_at_creation: false,
        }));
}

/// Updates the app status text at the top of the screen.
fn update_status_text(
    saved_indirect_parameters: Res<SavedIndirectParameters>,
    mut texts: Query<&mut Text>,
    meshes: Query<Entity, With<Mesh3d>>,
    app_status: Res<AppStatus>,
) {
    // How many meshes are in the scene?
    let total_mesh_count = meshes.iter().count();

    // Sample the rendered object count. Note that we don't synchronize beyond
    // locking the data and therefore this will value will generally at least
    // one frame behind. This is fine; this app is just a demonstration after
    // all.
    let (
        rendered_object_count,
        occlusion_culling_supported,
        occlusion_culling_introspection_supported,
    ): (u32, bool, bool) = {
        let saved_indirect_parameters = saved_indirect_parameters.lock().unwrap();
        let Some(saved_indirect_parameters) = saved_indirect_parameters.as_ref() else {
            // Bail out early if the resource isn't initialized yet.
            return;
        };
        (
            saved_indirect_parameters
                .data
                .iter()
                .take(saved_indirect_parameters.count as usize)
                .map(|indirect_parameters| indirect_parameters.instance_count)
                .sum(),
            saved_indirect_parameters.occlusion_culling_supported,
            saved_indirect_parameters.occlusion_culling_introspection_supported,
        )
    };

    // Change the text.
    for mut text in &mut texts {
        text.0 = String::new();
        if !occlusion_culling_supported {
            text.0
                .push_str("Occlusion culling not supported on this platform");
            continue;
        }

        let _ = writeln!(
            &mut text.0,
            "Occlusion culling {} (Press Space to toggle)",
            if app_status.occlusion_culling {
                "ON"
            } else {
                "OFF"
            },
        );

        if !occlusion_culling_introspection_supported {
            continue;
        }

        let _ = write!(
            &mut text.0,
            "{rendered_object_count}/{total_mesh_count} meshes rendered"
        );
    }
}

/// A system that reads the indirect parameters back from the GPU so that we can
/// report how many meshes were culled.
fn readback_indirect_parameters(
    mut indirect_parameters_staging_buffers: ResMut<IndirectParametersStagingBuffers>,
    saved_indirect_parameters: Res<SavedIndirectParameters>,
) {
    // If culling isn't supported on this platform, bail.
    if !saved_indirect_parameters
        .lock()
        .unwrap()
        .as_ref()
        .unwrap()
        .occlusion_culling_supported
    {
        return;
    }

    // Grab the staging buffers.
    let (Some(data_buffer), Some(batch_sets_buffer)) = (
        indirect_parameters_staging_buffers.data.take(),
        indirect_parameters_staging_buffers.batch_sets.take(),
    ) else {
        return;
    };

    // Read the GPU buffers back.
    let saved_indirect_parameters_0 = (**saved_indirect_parameters).clone();
    let saved_indirect_parameters_1 = (**saved_indirect_parameters).clone();
    readback_buffer::<IndirectParametersIndexed>(data_buffer, move |indirect_parameters| {
        saved_indirect_parameters_0
            .lock()
            .unwrap()
            .as_mut()
            .unwrap()
            .data = indirect_parameters.to_vec();
    });
    readback_buffer::<u32>(batch_sets_buffer, move |indirect_parameters_count| {
        saved_indirect_parameters_1
            .lock()
            .unwrap()
            .as_mut()
            .unwrap()
            .count = indirect_parameters_count[0];
    });
}

pub fn try_lock( &self, ) -> Result<MutexGuard<'_, T>, TryLockError<MutexGuard<'_, T>>>

Attempts to acquire this lock.

If the lock could not be acquired at this time, then Err is returned. Otherwise, an RAII guard is returned. The lock will be unlocked when the guard is dropped.

This function does not block.

Errors

If another user of this mutex panicked while holding the mutex, then this call will return the Poisoned error if the mutex would otherwise be acquired. An acquired lock guard will be contained in the returned error.

If the mutex could not be acquired because it is already locked, then this call will return the WouldBlock error.

Examples

use std::sync::{Arc, Mutex};
use std::thread;

let mutex = Arc::new(Mutex::new(0));
let c_mutex = Arc::clone(&mutex);

thread::spawn(move || {
    let mut lock = c_mutex.try_lock();
    if let Ok(ref mut mutex) = lock {
        **mutex = 10;
    } else {
        println!("try_lock failed");
    }
}).join().expect("thread::spawn failed");
assert_eq!(*mutex.lock().unwrap(), 10);

pub fn is_poisoned(&self) -> bool

Determines whether the mutex is poisoned.

If another thread is active, the mutex can still become poisoned at any time. You should not trust a false value for program correctness without additional synchronization.

Examples

use std::sync::{Arc, Mutex};
use std::thread;

let mutex = Arc::new(Mutex::new(0));
let c_mutex = Arc::clone(&mutex);

let _ = thread::spawn(move || {
    let _lock = c_mutex.lock().unwrap();
    panic!(); // the mutex gets poisoned
}).join();
assert_eq!(mutex.is_poisoned(), true);

pub fn clear_poison(&self)

Clear the poisoned state from a mutex.

If the mutex is poisoned, it will remain poisoned until this function is called. This allows recovering from a poisoned state and marking that it has recovered. For example, if the value is overwritten by a known-good value, then the mutex can be marked as un-poisoned. Or possibly, the value could be inspected to determine if it is in a consistent state, and if so the poison is removed.

Examples

use std::sync::{Arc, Mutex};
use std::thread;

let mutex = Arc::new(Mutex::new(0));
let c_mutex = Arc::clone(&mutex);

let _ = thread::spawn(move || {
    let _lock = c_mutex.lock().unwrap();
    panic!(); // the mutex gets poisoned
}).join();

assert_eq!(mutex.is_poisoned(), true);
let x = mutex.lock().unwrap_or_else(|mut e| {
    **e.get_mut() = 1;
    mutex.clear_poison();
    e.into_inner()
});
assert_eq!(mutex.is_poisoned(), false);
assert_eq!(*x, 1);

pub fn into_inner(self) -> Result<T, PoisonError<T>>

Consumes this mutex, returning the underlying data.

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error containing the underlying data instead.

Examples

use std::sync::Mutex;

let mutex = Mutex::new(0);
assert_eq!(mutex.into_inner().unwrap(), 0);

pub fn get_mut(&mut self) -> Result<&mut T, PoisonError<&mut T>>

Returns a mutable reference to the underlying data.

Since this call borrows the Mutex mutably, no actual locking needs to take place – the mutable borrow statically guarantees no new locks can be acquired while this reference exists. Note that this method does not clear any previous abandoned locks (e.g., via forget() on a MutexGuard).

Errors

If another user of this mutex panicked while holding the mutex, then this call will return an error containing a mutable reference to the underlying data instead.

Examples

use std::sync::Mutex;

let mut mutex = Mutex::new(0);
*mutex.get_mut().unwrap() = 10;
assert_eq!(*mutex.lock().unwrap(), 10);

pub const fn data_ptr(&self) -> *mut T

🔬This is a nightly-only experimental API. (mutex_data_ptr)

Returns a raw pointer to the underlying data.

The returned pointer is always non-null and properly aligned, but it is the user’s responsibility to ensure that any reads and writes through it are properly synchronized to avoid data races, and that it is not read or written through after the mutex is dropped.

Trait Implementations

impl<T> Clear for Mutex<T>

where T: Clear,

fn clear(&mut self)

Clear all data in self, retaining the allocated capacithy.

impl<C> ClockSequence for Mutex<C>

where C: ClockSequence + RefUnwindSafe,

type Output = <C as ClockSequence>::Output

The type of sequence returned by this counter.

fn generate_sequence( &self, seconds: u64, subsec_nanos: u32, ) -> <Mutex<C> as ClockSequence>::Output

Get the next value in the sequence to feed into a timestamp.

fn generate_timestamp_sequence( &self, seconds: u64, subsec_nanos: u32, ) -> (<Mutex<C> as ClockSequence>::Output, u64, u32)

Get the next value in the sequence, potentially also adjusting the timestamp.

fn usable_bits(&self) -> usize

where <Mutex<C> as ClockSequence>::Output: Sized,

The number of usable bits from the least significant bit in the result of ClockSequence::generate_sequence or ClockSequence::generate_timestamp_sequence.

impl<T> Debug for Mutex<T>

where T: Debug + ?Sized,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> Default for Mutex<T>

where T: Default + ?Sized,

fn default() -> Mutex<T>

Creates a Mutex<T>, with the Default value for T.

impl<'de, T> Deserialize<'de> for Mutex<T>

where T: Deserialize<'de>,

fn deserialize<D>( deserializer: D, ) -> Result<Mutex<T>, <D as Deserializer<'de>>::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<T> From<T> for Mutex<T>

fn from(t: T) -> Mutex<T>

Creates a new mutex in an unlocked state ready for use. This is equivalent to Mutex::new.

impl<'a, W> MakeWriter<'a> for Mutex<W>

where W: Write + 'a,

type Writer = MutexGuardWriter<'a, W>

The concrete io::Write implementation returned by make_writer.

fn make_writer(&'a self) -> <Mutex<W> as MakeWriter<'a>>::Writer

Returns an instance of Writer.

fn make_writer_for(&'a self, meta: &Metadata<'_>) -> Self::Writer

Returns a Writer for writing data from the span or event described by the provided Metadata.

impl<T> Serialize for Mutex<T>

where T: Serialize + ?Sized,

fn serialize<S>( &self, serializer: S, ) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl SubscriberList for Mutex<HashSet<ReactiveContext>>

fn add(&self, subscriber: ReactiveContext)

Add a subscriber to the list.

fn remove(&self, subscriber: &ReactiveContext)

Remove a subscriber from the list.

fn visit(&self, f: &mut dyn FnMut(&ReactiveContext))

Visit all subscribers in the list.

impl<T> Type for Mutex<T>

where T: Type + ?Sized,

const SIGNATURE: &'static Signature = T::SIGNATURE

The signature for the implementing type, in parsed format.

impl<T> RefUnwindSafe for Mutex<T>

where T: ?Sized,

impl<T> Send for Mutex<T>

where T: Send + ?Sized,

T must be Send for a Mutex to be Send because it is possible to acquire the owned T from the Mutex via into_inner.

impl<T> Sync for Mutex<T>

where T: Send + ?Sized,

T must be Send for Mutex to be Sync. This ensures that the protected data can be accessed safely from multiple threads without causing data races or other unsafe behavior.

Mutex<T> provides mutable access to T to one thread at a time. However, it’s essential for T to be Send because it’s not safe for non-Send structures to be accessed in this manner. For instance, consider Rc, a non-atomic reference counted smart pointer, which is not Send. With Rc, we can have multiple copies pointing to the same heap allocation with a non-atomic reference count. If we were to use Mutex<Rc<_>>, it would only protect one instance of Rc from shared access, leaving other copies vulnerable to potential data races.

Also note that it is not necessary for T to be Sync as &T is only made available to one thread at a time if T is not Sync.

impl<T> UnwindSafe for Mutex<T>

where T: ?Sized,