shared_memory/
lib.rs

1//! A thin wrapper around shared memory system calls
2//!
3//! For help on how to get started, take a look at the [examples](https://github.com/elast0ny/shared_memory-rs/tree/master/examples) !
4
5use std::fs::{File, OpenOptions};
6use std::io::{ErrorKind, Read, Write};
7
8use std::fs::remove_file;
9use std::path::{Path, PathBuf};
10
11use cfg_if::cfg_if;
12
13cfg_if! {
14    if #[cfg(feature = "logging")] {
15        pub use log;
16    } else {
17        #[allow(unused_macros)]
18        mod log {
19            macro_rules! trace (($($tt:tt)*) => {{}});
20            macro_rules! debug (($($tt:tt)*) => {{}});
21            macro_rules! info (($($tt:tt)*) => {{}});
22            macro_rules! warn (($($tt:tt)*) => {{}});
23            macro_rules! error (($($tt:tt)*) => {{}});
24            pub(crate) use {debug, trace};
25        }
26    }
27}
28
29use crate::log::*;
30
31mod error;
32pub use error::*;
33
34//Load up the proper OS implementation
35cfg_if! {
36    if #[cfg(target_os="windows")] {
37        mod windows;
38        use windows as os_impl;
39    } else if #[cfg(any(target_os="freebsd", target_os="linux", target_os="macos"))] {
40        mod unix;
41        use crate::unix as os_impl;
42    } else {
43        compile_error!("shared_memory isnt implemented for this platform...");
44    }
45}
46
47#[derive(Clone, Default)]
48/// Struct used to configure different parameters before creating a shared memory mapping
49pub struct ShmemConf {
50    owner: bool,
51    os_id: Option<String>,
52    overwrite_flink: bool,
53    flink_path: Option<PathBuf>,
54    size: usize,
55    ext: os_impl::ShmemConfExt,
56}
57impl Drop for ShmemConf {
58    fn drop(&mut self) {
59        // Delete the flink if we are the owner of the mapping
60        if self.owner {
61            if let Some(flink_path) = self.flink_path.as_ref() {
62                debug!("Deleting file link {}", flink_path.to_string_lossy());
63                let _ = remove_file(flink_path);
64            }
65        }
66    }
67}
68
69impl ShmemConf {
70    /// Create a new default shmem config
71    pub fn new() -> Self {
72        ShmemConf::default()
73    }
74    /// Provide a specific os identifier for the mapping
75    ///
76    /// When not specified, a randomly generated identifier will be used
77    pub fn os_id<S: AsRef<str>>(mut self, os_id: S) -> Self {
78        self.os_id = Some(String::from(os_id.as_ref()));
79        self
80    }
81
82    /// Overwrites file links if it already exist when calling `create()`
83    pub fn force_create_flink(mut self) -> Self {
84        self.overwrite_flink = true;
85        self
86    }
87
88    /// Create the shared memory mapping with a file link
89    ///
90    /// This creates a file on disk that contains the unique os_id for the mapping.
91    /// This can be useful when application want to rely on filesystems to share mappings
92    pub fn flink<S: AsRef<Path>>(mut self, path: S) -> Self {
93        self.flink_path = Some(PathBuf::from(path.as_ref()));
94        self
95    }
96
97    /// Sets the size of the mapping that will be used in `create()`
98    pub fn size(mut self, size: usize) -> Self {
99        self.size = size;
100        self
101    }
102
103    /// Create a new mapping using the current configuration
104    pub fn create(mut self) -> Result<Shmem, ShmemError> {
105        if self.size == 0 {
106            return Err(ShmemError::MapSizeZero);
107        }
108
109        if let Some(ref flink_path) = self.flink_path {
110            if !self.overwrite_flink && flink_path.is_file() {
111                return Err(ShmemError::LinkExists);
112            }
113        }
114
115        // Create the mapping
116        let mapping = match self.os_id {
117            None => {
118                // Generate random ID until one works
119                loop {
120                    let cur_id = format!("/shmem_{:X}", rand::random::<u64>());
121                    match os_impl::create_mapping(&cur_id, self.size) {
122                        Err(ShmemError::MappingIdExists) => continue,
123                        Ok(m) => break m,
124                        Err(e) => {
125                            return Err(e);
126                        }
127                    };
128                }
129            }
130            Some(ref specific_id) => os_impl::create_mapping(specific_id, self.size)?,
131        };
132        debug!("Created shared memory mapping '{}'", mapping.unique_id);
133
134        // Create flink
135        if let Some(ref flink_path) = self.flink_path {
136            debug!("Creating file link that points to mapping");
137            let mut open_options: OpenOptions = OpenOptions::new();
138            open_options.write(true);
139
140            if self.overwrite_flink {
141                open_options.create(true).truncate(true);
142            } else {
143                open_options.create_new(true);
144            }
145
146            match open_options.open(flink_path) {
147                Ok(mut f) => {
148                    // write the shmem uid asap
149                    if let Err(e) = f.write(mapping.unique_id.as_bytes()) {
150                        let _ = std::fs::remove_file(flink_path);
151                        return Err(ShmemError::LinkWriteFailed(e));
152                    }
153                }
154                Err(e) if e.kind() == ErrorKind::AlreadyExists => {
155                    return Err(ShmemError::LinkExists)
156                }
157                Err(e) => return Err(ShmemError::LinkCreateFailed(e)),
158            }
159
160            debug!(
161                "Created file link '{}' with id '{}'",
162                flink_path.to_string_lossy(),
163                mapping.unique_id
164            );
165        }
166
167        self.owner = true;
168        self.size = mapping.map_size;
169
170        Ok(Shmem {
171            config: self,
172            mapping,
173        })
174    }
175
176    /// Opens an existing mapping using the current configuration
177    pub fn open(mut self) -> Result<Shmem, ShmemError> {
178        // Must at least have a flink or an os_id
179        if self.flink_path.is_none() && self.os_id.is_none() {
180            debug!("Open called with no file link or unique id...");
181            return Err(ShmemError::NoLinkOrOsId);
182        }
183
184        let mut flink_uid = String::new();
185        let mut retry = 0;
186        loop {
187            let unique_id = if let Some(ref unique_id) = self.os_id {
188                retry = 5;
189                unique_id.as_str()
190            } else {
191                let flink_path = self.flink_path.as_ref().unwrap();
192                debug!(
193                    "Open shared memory from file link {}",
194                    flink_path.to_string_lossy()
195                );
196                let mut f = match File::open(flink_path) {
197                    Ok(f) => f,
198                    Err(e) => return Err(ShmemError::LinkOpenFailed(e)),
199                };
200                flink_uid.clear();
201                if let Err(e) = f.read_to_string(&mut flink_uid) {
202                    return Err(ShmemError::LinkReadFailed(e));
203                }
204                flink_uid.as_str()
205            };
206
207            match os_impl::open_mapping(unique_id, self.size, &self.ext) {
208                Ok(m) => {
209                    self.size = m.map_size;
210                    self.owner = false;
211
212                    return Ok(Shmem {
213                        config: self,
214                        mapping: m,
215                    });
216                }
217                // If we got this failing os_id from the flink, try again in case the shmem owner didnt write the full
218                // unique_id to the file
219                Err(ShmemError::MapOpenFailed(_)) if self.os_id.is_none() && retry < 5 => {
220                    retry += 1;
221                    std::thread::sleep(std::time::Duration::from_millis(50));
222                }
223                Err(e) => return Err(e),
224            }
225        }
226    }
227}
228
229/// Structure used to extract information from an existing shared memory mapping
230pub struct Shmem {
231    config: ShmemConf,
232    mapping: os_impl::MapData,
233}
234#[allow(clippy::len_without_is_empty)]
235impl Shmem {
236    /// Returns whether we created the mapping or not
237    pub fn is_owner(&self) -> bool {
238        self.config.owner
239    }
240    /// Allows for gaining/releasing ownership of the mapping
241    ///
242    /// Warning : You must ensure at least one process owns the mapping in order to ensure proper cleanup code is ran
243    pub fn set_owner(&mut self, is_owner: bool) -> bool {
244        self.mapping.set_owner(is_owner);
245
246        let prev_val = self.config.owner;
247        self.config.owner = is_owner;
248        prev_val
249    }
250    /// Returns the OS unique identifier for the mapping
251    pub fn get_os_id(&self) -> &str {
252        self.mapping.unique_id.as_str()
253    }
254    /// Returns the flink path if present
255    pub fn get_flink_path(&self) -> Option<&PathBuf> {
256        self.config.flink_path.as_ref()
257    }
258    /// Returns the total size of the mapping
259    pub fn len(&self) -> usize {
260        self.mapping.map_size
261    }
262    /// Returns a raw pointer to the mapping
263    pub fn as_ptr(&self) -> *mut u8 {
264        self.mapping.as_mut_ptr()
265    }
266    /// Returns mapping as a byte slice
267    /// # Safety
268    /// This function is unsafe because it is impossible to ensure the range of bytes is immutable
269    pub unsafe fn as_slice(&self) -> &[u8] {
270        std::slice::from_raw_parts(self.as_ptr(), self.len())
271    }
272    /// Returns mapping as a mutable byte slice
273    /// # Safety
274    /// This function is unsafe because it is impossible to ensure the returned mutable refence is unique/exclusive
275    pub unsafe fn as_slice_mut(&mut self) -> &mut [u8] {
276        std::slice::from_raw_parts_mut(self.as_ptr(), self.len())
277    }
278}
shared_memory/lib.rs

shared_memory/
lib.rs
