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    // Copyright (c) 2016 The vulkano developers
    // Licensed under the Apache License, Version 2.0
    // <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT
    // license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
    // at your option. All files in the project carrying such
    // notice may not be copied, modified, or distributed except
    // according to those terms.

    use std::mem;
    use std::ptr;
    use std::sync::Arc;

    use OomError;
    use SafeDeref;
    use VulkanObject;
    use check_errors;
    use device::Device;
    use device::DeviceOwned;
    use vk;

    /// Used to provide synchronization between command buffers during their execution.
    ///
    /// It is similar to a fence, except that it is purely on the GPU side. The CPU can't query a
    /// semaphore's status or wait for it to be signaled.
    #[derive(Debug)]
    pub struct Semaphore<D = Arc<Device>>
        where D: SafeDeref<Target = Device>
    {
        semaphore: vk::Semaphore,
        device: D,
        must_put_in_pool: bool,
    }

    impl<D> Semaphore<D>
        where D: SafeDeref<Target = Device>
    {
        /// Takes a semaphore from the vulkano-provided semaphore pool.
        /// If the pool is empty, a new semaphore will be allocated.
        /// Upon `drop`, the semaphore is put back into the pool.
        ///
        /// For most applications, using the pool should be preferred,
        /// in order to avoid creating new semaphores every frame.
        pub fn from_pool(device: D) -> Result<Semaphore<D>, OomError> {
            let maybe_raw_sem = device.semaphore_pool().lock().unwrap().pop();
            match maybe_raw_sem {
                Some(raw_sem) => {
                    Ok(Semaphore {
                           device: device,
                           semaphore: raw_sem,
                           must_put_in_pool: true,
                       })
                },
                None => {
                    // Pool is empty, alloc new semaphore
                    Semaphore::alloc_impl(device, true)
                },
            }
        }

        /// Builds a new semaphore.
        #[inline]
        pub fn alloc(device: D) -> Result<Semaphore<D>, OomError> {
            Semaphore::alloc_impl(device, false)
        }

        fn alloc_impl(device: D, must_put_in_pool: bool) -> Result<Semaphore<D>, OomError> {
            let semaphore = unsafe {
                // since the creation is constant, we use a `static` instead of a struct on the stack
                static mut INFOS: vk::SemaphoreCreateInfo = vk::SemaphoreCreateInfo {
                    sType: vk::STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO,
                    pNext: 0 as *const _, // ptr::null()
                    flags: 0, // reserved
                };

                let vk = device.pointers();
                let mut output = mem::uninitialized();
                check_errors(vk.CreateSemaphore(device.internal_object(),
                                                &INFOS,
                                                ptr::null(),
                                                &mut output))?;
                output
            };

            Ok(Semaphore {
                   device: device,
                   semaphore: semaphore,
                   must_put_in_pool: must_put_in_pool,
               })
        }
    }

    unsafe impl DeviceOwned for Semaphore {
        #[inline]
        fn device(&self) -> &Arc<Device> {
            &self.device
        }
    }

    unsafe impl<D> VulkanObject for Semaphore<D>
        where D: SafeDeref<Target = Device>
    {
        type Object = vk::Semaphore;

        const TYPE: vk::DebugReportObjectTypeEXT = vk::DEBUG_REPORT_OBJECT_TYPE_SEMAPHORE_EXT;

        #[inline]
        fn internal_object(&self) -> vk::Semaphore {
            self.semaphore
        }
    }

    impl<D> Drop for Semaphore<D>
        where D: SafeDeref<Target = Device>
    {
        #[inline]
        fn drop(&mut self) {
            unsafe {
                if self.must_put_in_pool {
                    let raw_sem = self.semaphore;
                    self.device.semaphore_pool().lock().unwrap().push(raw_sem);
                } else {
                    let vk = self.device.pointers();
                    vk.DestroySemaphore(self.device.internal_object(), self.semaphore, ptr::null());
                }
            }
        }
    }

    #[cfg(test)]
    mod tests {
        use VulkanObject;
        use sync::Semaphore;

        #[test]
        fn semaphore_create() {
            let (device, _) = gfx_dev_and_queue!();
            let _ = Semaphore::alloc(device.clone());
        }

        #[test]
        fn semaphore_pool() {
            let (device, _) = gfx_dev_and_queue!();

            assert_eq!(device.semaphore_pool().lock().unwrap().len(), 0);
            let sem1_internal_obj = {
                let sem = Semaphore::from_pool(device.clone()).unwrap();
                assert_eq!(device.semaphore_pool().lock().unwrap().len(), 0);
                sem.internal_object()
            };

            assert_eq!(device.semaphore_pool().lock().unwrap().len(), 1);
            let sem2 = Semaphore::from_pool(device.clone()).unwrap();
            assert_eq!(device.semaphore_pool().lock().unwrap().len(), 0);
            assert_eq!(sem2.internal_object(), sem1_internal_obj);
        }
    }

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