servo_base/generic_channel/
shared_memory.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5use std::fmt;
6use std::ops::Deref;
7use std::sync::Arc;
8
9use ipc_channel::ipc::IpcSharedMemory;
10use malloc_size_of::MallocSizeOf;
11use serde::de::VariantAccess;
12use serde::{Deserialize, Deserializer, Serialize, Serializer};
13
14use crate::generic_channel::use_ipc;
15
16#[derive(Clone)]
17pub struct GenericSharedMemory(GenericSharedMemoryVariant);
18
19#[derive(Clone)]
20enum GenericSharedMemoryVariant {
21    Ipc(IpcSharedMemory),
22    InProcess(Arc<Vec<u8>>),
23}
24
25impl AsRef<[u8]> for GenericSharedMemory {
26    fn as_ref(&self) -> &[u8] {
27        self
28    }
29}
30
31impl Deref for GenericSharedMemory {
32    type Target = [u8];
33
34    #[inline]
35    fn deref(&self) -> &[u8] {
36        match &self.0 {
37            GenericSharedMemoryVariant::Ipc(ipc_shared_memory) => ipc_shared_memory,
38            GenericSharedMemoryVariant::InProcess(items) => items.as_slice(),
39        }
40    }
41}
42
43impl MallocSizeOf for GenericSharedMemory {
44    fn size_of(&self, ops: &mut malloc_size_of::MallocSizeOfOps) -> usize {
45        match &self.0 {
46            GenericSharedMemoryVariant::Ipc(_) => 0,
47            GenericSharedMemoryVariant::InProcess(items) => items.size_of(ops),
48        }
49    }
50}
51
52impl GenericSharedMemory {
53    pub fn from_bytes(bytes: &[u8]) -> Self {
54        if use_ipc() {
55            GenericSharedMemory(GenericSharedMemoryVariant::Ipc(
56                IpcSharedMemory::from_bytes(bytes),
57            ))
58        } else {
59            GenericSharedMemory(GenericSharedMemoryVariant::InProcess(Arc::new(
60                bytes.to_owned(),
61            )))
62        }
63    }
64
65    pub fn from_byte(data: u8, length: usize) -> Self {
66        if use_ipc() {
67            GenericSharedMemory(GenericSharedMemoryVariant::Ipc(IpcSharedMemory::from_byte(
68                data, length,
69            )))
70        } else {
71            GenericSharedMemory(GenericSharedMemoryVariant::InProcess(Arc::new(vec![
72                data;
73                length
74            ])))
75        }
76    }
77
78    /// Build a `GenericSharedMemory` from a `Vec<u8>`.
79    ///
80    /// In single-process mode this allows reusing the Vec and the only cost is
81    /// allocating a new Arc. Prefer over `Self::from_bytes` if ownership is
82    /// transferred.
83    pub fn from_vec(bytes: Vec<u8>) -> Self {
84        if use_ipc() {
85            GenericSharedMemory(GenericSharedMemoryVariant::Ipc(
86                IpcSharedMemory::from_bytes(&bytes),
87            ))
88        } else {
89            GenericSharedMemory(GenericSharedMemoryVariant::InProcess(Arc::new(bytes)))
90        }
91    }
92
93    /// Build a `GenericSharedMemory` from an `Arc<Vec<u8>>`.
94    ///
95    /// In single-process mode this allows creating shared memory without copying.
96    pub fn from_arc_vec(arc: Arc<Vec<u8>>) -> Self {
97        if use_ipc() {
98            GenericSharedMemory(GenericSharedMemoryVariant::Ipc(
99                IpcSharedMemory::from_bytes(&arc),
100            ))
101        } else {
102            GenericSharedMemory(GenericSharedMemoryVariant::InProcess(arc))
103        }
104    }
105
106    /// Free operation in single process mode.
107    /// If multiple `GenericSharedmemory` point to the same value this is safe to use and only effects the value currently hold.
108    pub fn into_arc_vec(self) -> Arc<Vec<u8>> {
109        match self.0 {
110            GenericSharedMemoryVariant::Ipc(ipc_shared_memory) => {
111                Arc::new(ipc_shared_memory.to_vec())
112            },
113            GenericSharedMemoryVariant::InProcess(arc) => arc,
114        }
115    }
116
117    pub fn from_bytes_with_mutator(bytes: &[u8], mutator: impl FnOnce(&mut [u8])) -> Self {
118        let mut shared_memory = Self::from_bytes(bytes);
119        match &mut shared_memory.0 {
120            GenericSharedMemoryVariant::Ipc(ipc_shared_memory) => {
121                #[expect(unsafe_code)]
122                unsafe {
123                    mutator(ipc_shared_memory.deref_mut())
124                }
125            },
126            GenericSharedMemoryVariant::InProcess(arc) => mutator(
127                Arc::get_mut(arc)
128                    .expect("Arc just created from bytes")
129                    .as_mut_slice(),
130            ),
131        }
132        shared_memory
133    }
134}
135
136impl fmt::Debug for GenericSharedMemory {
137    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
138        f.debug_tuple("GenericSharedMemory").finish()
139    }
140}
141
142impl Serialize for GenericSharedMemory {
143    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
144        match &self.0 {
145            GenericSharedMemoryVariant::Ipc(memory) => {
146                s.serialize_newtype_variant("GenericSharedMemory", 0, "Ipc", memory)
147            },
148            GenericSharedMemoryVariant::InProcess(arc) => {
149                if use_ipc() {
150                    return Err(serde::ser::Error::custom(
151                        "Arc<Vec<u8>> found in multiprocess mode!",
152                    ));
153                } // We know everything is in one address-space, so we can "serialize" the receiver by
154                // sending a leaked Arc pointer.
155                let address = Arc::into_raw(arc.clone()) as *mut Vec<u8> as usize;
156                s.serialize_newtype_variant("GenericSharedMemory", 1, "InProcess", &address)
157            },
158        }
159    }
160}
161
162struct GenericSharedMemoryVisitor {}
163
164impl<'de> serde::de::Visitor<'de> for GenericSharedMemoryVisitor {
165    type Value = GenericSharedMemory;
166
167    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
168        formatter.write_str("a GenericReceiver variant")
169    }
170
171    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
172    where
173        A: serde::de::EnumAccess<'de>,
174    {
175        #[derive(Deserialize)]
176        enum GenericSharedMemoryVariantNames {
177            Ipc,
178            InProcess,
179        }
180
181        let (variant_name, variant_data): (GenericSharedMemoryVariantNames, _) = data.variant()?;
182
183        match variant_name {
184            GenericSharedMemoryVariantNames::Ipc => variant_data
185                .newtype_variant::<IpcSharedMemory>()
186                .map(|receiver| GenericSharedMemory(GenericSharedMemoryVariant::Ipc(receiver))),
187            GenericSharedMemoryVariantNames::InProcess => {
188                if use_ipc() {
189                    return Err(serde::de::Error::custom(
190                        "Arc data found in multiprocess mode!",
191                    ));
192                }
193                let addr = variant_data.newtype_variant::<usize>()?;
194                let ptr = addr as *mut Vec<u8>;
195                // SAFETY: We know we are in the same address space as the sender, so we can safely
196                // reconstruct the Arc.
197                #[expect(unsafe_code)]
198                let arc = unsafe { Arc::from_raw(ptr) };
199                Ok(GenericSharedMemory(GenericSharedMemoryVariant::InProcess(
200                    arc,
201                )))
202            },
203        }
204    }
205}
206
207impl<'a> Deserialize<'a> for GenericSharedMemory {
208    fn deserialize<D>(d: D) -> Result<GenericSharedMemory, D::Error>
209    where
210        D: Deserializer<'a>,
211    {
212        d.deserialize_enum(
213            "GenericSharedMemory",
214            &["Ipc", "InProcess"],
215            GenericSharedMemoryVisitor {},
216        )
217    }
218}
219
220#[cfg(test)]
221mod single_process_shared_memory_test {
222    use std::sync::Arc;
223
224    use ipc_channel::ipc::IpcSharedMemory;
225
226    use super::GenericSharedMemory;
227    use crate::generic_channel::{self};
228
229    #[test]
230    fn test_ipc() {
231        let bytes = vec![0xba; 10];
232        let bytes_copy = bytes.clone();
233        let shared_memory = GenericSharedMemory(super::GenericSharedMemoryVariant::Ipc(
234            IpcSharedMemory::from_bytes(&bytes),
235        ));
236
237        let (send, recv) = generic_channel::channel().unwrap();
238        send.send(shared_memory).expect("Could not send");
239        assert_eq!(recv.recv().unwrap().to_vec(), bytes_copy);
240    }
241
242    #[test]
243    fn test_inprocess() {
244        let bytes = vec![0xba; 10];
245        let bytes_copy = bytes.clone();
246        let shared_memory = GenericSharedMemory(super::GenericSharedMemoryVariant::InProcess(
247            Arc::new(bytes.clone()),
248        ));
249
250        let (send, recv) = generic_channel::channel().unwrap();
251        send.send(shared_memory).expect("Could not send");
252        assert_eq!(recv.recv().unwrap().to_vec(), bytes_copy);
253    }
254}
servo_base/generic_channel/shared_memory.rs

servo_base/generic_channel/
shared_memory.rs
