algeon-cugraph 0.1.2

//! Random number generator state for cuGraph algorithms.
//!
//! Safe owner for `cugraph_rng_state_t` on the bound CUDA device.
//!
//! # Example
//!
//! ```no_run
//! use cudf::Runtime;
//! use cugraph::{ResourceHandle, random::RngState};
//!
//! let runtime = std::sync::Arc::new(Runtime::new().unwrap());
//! let handle =
//!     ResourceHandle::for_runtime(std::sync::Arc::clone(&runtime)).unwrap();
//! let entered = handle.enter("RngState docs").unwrap();
//! let rng = RngState::new(&entered, 42).unwrap();
//! ```

use std::{marker::PhantomData, ptr};

use cugraph_sys::{cugraph_error_t, cugraph_rng_state_create, cugraph_rng_state_t};

use crate::{
    cuda::{DeviceResourceKind, drop_device_resource},
    error::{Result, check_error, require_non_null},
    handle::{EnteredContext, ResourceHandleLease},
};

/// RAII wrapper around `cugraph_rng_state_t`.
///
/// The RNG state is used by stochastic algorithms and is updated in-place
/// with each call. Not thread-safe; must be used from the thread that
/// created it.
pub struct RngState {
    raw: *mut cugraph_rng_state_t,
    device: i32,
    // Keeps a runtime-bound cuGraph handle alive until after Drop frees `raw`.
    _resource_handle_lease: Option<ResourceHandleLease>,
    _nosend_nosync: PhantomData<*mut ()>,
}

impl std::fmt::Debug for RngState {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("RngState").finish_non_exhaustive()
    }
}

impl RngState {
    /// Create a new RNG state with the given seed.
    ///
    /// Different seeds produce different random sequences. In multi-GPU
    /// settings, each GPU should use a different seed.
    pub fn new(handle: &EnteredContext<'_>, seed: u64) -> Result<Self> {
        let mut raw: *mut cugraph_rng_state_t = ptr::null_mut();
        let mut error: *mut cugraph_error_t = ptr::null_mut();

        // SAFETY: `handle` outlives the call and `raw`/`error` are valid
        // out-pointers for cuGraph to initialize.
        unsafe {
            let code = cugraph_rng_state_create(handle.handle_ptr(), seed, &mut raw, &mut error);
            check_error(code, error, handle.device(), "RngState::new")?;
        }

        let raw = require_non_null(raw, "RngState::new", "rng_state")?;

        Ok(Self {
            raw,
            device: handle.device(),
            _resource_handle_lease: handle.runtime_bound_lease(),
            _nosend_nosync: PhantomData,
        })
    }

    /// Get the raw C pointer. For internal use by other modules.
    pub(crate) fn as_ptr(&mut self) -> *mut cugraph_rng_state_t {
        self.raw
    }
}

impl Drop for RngState {
    fn drop(&mut self) {
        drop_device_resource(&mut self.raw, self.device, "RngState::drop", DeviceResourceKind::RngState);
    }
}

#[cfg(test)]
mod tests {

    use super::*;
    use crate::ResourceHandle;

    #[test]
    fn runtime_bound_rng_state_retains_native_owner_until_drop() {
        let runtime = std::sync::Arc::new(cudf::Runtime::builder().build().expect("runtime"));
        let handle = ResourceHandle::for_runtime(runtime).expect("runtime-bound handle");
        let rng = {
            let entered = handle.enter("runtime_bound_rng_state_retains_native_owner_until_drop").expect("entered");
            RngState::new(&entered, 42).expect("rng state")
        };

        drop(handle);
        let lease = rng._resource_handle_lease.as_ref().expect("runtime-bound rng should retain its native owner");
        let mut entered_after_handle_drop = false;
        lease.with_teardown_gate(|| entered_after_handle_drop = true);
        assert!(entered_after_handle_drop, "the RNG lease must keep the native owner live after its handle drops");
        drop(rng);
    }
}