[英]Send can only be implemented for a struct/enum type, not a trait
I have having difficulty implementing Send
for a trait. 我很难实现
Send
特质。 Full code in the playground . 操场上的完整代码 。
I have a Storage
trait : 我有一个
Storage
特征:
pub trait Storage {
fn get_value(&self, key: &str) -> Result<Vec<u8>, Error>;
fn put_value(&mut self, key: &str, value: &[u8]) -> Result<(), Error>;
fn key_exists(&self, key: &str) -> bool;
fn delete_key(&mut self, key: &str) -> Result<(), Error>;
}
It is part of the Consistency
struct: 它是
Consistency
结构的一部分:
pub struct Consistency<'a> {
storage: &'a mut Storage,
}
I have implemented a MemoryStorage
struct: 我已经实现了一个
MemoryStorage
结构:
#[derive(Debug)]
struct MemoryStorage {
data: HashMap<String, Vec<u8>>,
}
impl Storage for MemoryStorage {
fn get_value(&self, key: &str) -> Result<Vec<u8>, Error> {
self.data.get(key).map_or(
Err(Error::new(ErrorKind::NotFound, "Key does not exists")),
|v| Ok(v.clone()),
)
}
fn put_value(&mut self, key: &str, value: &[u8]) -> Result<(), Error> {
self.data.insert(key.to_string(), Vec::from(value));
Ok(())
}
fn key_exists(&self, key: &str) -> bool {
self.data.contains_key(key)
}
fn delete_key(&mut self, key: &str) -> Result<(), Error> {
self.data.remove(key).map_or(
Err(Error::new(ErrorKind::NotFound, "Key does not exists")),
|v| Ok(()),
)
}
}
I wrote a test: 我写了一个测试:
#[test]
fn multiple_threads_bombing_storage() {
const parallels: usize = 10;
let mut storage = MemoryStorage {
data: HashMap::new(),
};
let mut consistency = Consistency::new(&mut storage);
// create all keys.
let mut keys = Vec::<String>::new();
for k in 1..parallels {
keys.push(k.to_string());
}
let zero = "0".as_bytes();
// put default values in files.
for key in keys.clone() {
consistency.put_value(&key, zero).unwrap();
}
// test write threads
let write_thread = |to_write: Vec<u8>, keys: &mut Vec<String>| {
let mut rng = rand::thread_rng();
rng.shuffle(keys);
for key in keys {
let mut val = consistency.get_value(key).unwrap();
val.append(to_write.clone().as_mut());
consistency.put_value(key, &val).unwrap();
}
};
// start parallels threads..
for t in 1..parallels {
let handle = thread::spawn(move || {
write_thread(t.to_string().into_bytes(), &mut keys);
});
}
// wait for all threads..
// check if all parallels keys have all numbers in any order.
}
This gives me an error: 这给我一个错误:
error[E0277]: the trait bound `fileapi::Storage: std::marker::Send` is not satisfied
--> src/consistency.rs:158:26
|
158 | let handle = thread::spawn(move || {
| ^^^^^^^^^^^^^ `fileapi::Storage` cannot be sent between threads safely
|
= help: the trait `std::marker::Send` is not implemented for `fileapi::Storage`
= note: required because of the requirements on the impl of `std::marker::Send` for `&mut fileapi::Storage`
= note: required because it appears within the type `consistency::Consistency<'_>`
= note: required because of the requirements on the impl of `std::marker::Send` for `&mut consistency::Consistency<'_>`
= note: required because it appears within the type `[closure@src/consistency.rs:145:28: 154:10 consistency:&mut consistency::Consistency<'_>]`
= note: required because it appears within the type `[closure@src/consistency.rs:158:40: 160:14 write_thread:[closure@src/consistency.rs:145:28: 154:10 consistency:&mut consistency::Consistency<'_>], t:usize, keys:std::vec::Vec<std::string::String>]`
= note: required by `std::thread::spawn`
Adding unsafe impl Send for Storage {}
gives me a contradictory error that Send
can't be implemented for a trait: 添加
unsafe impl Send for Storage {}
会给我带来一个矛盾的错误,即无法针对特征实施Send
:
cross-crate traits with a default impl, like `std::marker::Send`, can only be implemented for a struct/enum type, not `fileapi::Storage + 'static`
I don't understand how to solve this problem. 我不明白如何解决这个问题。
You have a reference to something implementing a trait (a trait object ), but your trait isn't guaranteed to be able to be sent between threads. 您对实现trait的对象 ( trait对象 )进行了引用,但是不能保证您的trait能够在线程之间发送。
You need to ensure that it is. 您需要确保它是。 You can require all implementors of your trait are
Send
: 您可以要求特征的所有实现者均为
Send
:
pub trait Storage: Send {
// ...
}
Or that this specific trait object implements Send
: 或者该特定特征对象实现
Send
:
pub struct Consistency<'a> {
storage: &'a mut (Storage + Send),
}
Your code has many other issues, so it still doesn't compile. 您的代码还有许多其他问题,因此仍然无法编译。 Among them:
其中:
You many need to go back and re-read The Rust Programming Language , especially the chapter on concurrency . 您很多人需要返回并重新阅读Rust编程语言 ,尤其是有关并发性的章节 。
See also: 也可以看看:
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