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Implement env_lock with RwLock

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Copying the approach of the Unix target, this change uses the standard
`RwLock` to protect against concurrent access of libc's environment.
This locking is only enabled when WebAssembly's `atomics` feature is
also enabled.
This commit is contained in:
Andrew Brown 2022-09-29 11:17:15 -07:00
parent da638b3a9f
commit 9530ba0fe2
1 changed files with 23 additions and 12 deletions
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35
library/std/src/sys/wasi/os.rs
View File

@ -1,11 +1,11 @@
#![deny(unsafe_op_in_unsafe_fn)]
use crate::any::Any;
use crate::error::Error as StdError;
use crate::ffi::{CStr, OsStr, OsString};
use crate::fmt;
use crate::io;
use crate::marker::PhantomData;
use crate::ops::Drop;
use crate::os::wasi::prelude::*;
use crate::path::{self, PathBuf};
use crate::str;
@ -24,13 +24,24 @@ mod libc {
}
}
pub unsafe fn env_lock() -> impl Any {
cfg_if::cfg_if! {
if #[cfg(target_feature = "atomics")] {
todo!()
} else {
// No need for a lock if we're single-threaded, but this function will need
// to get implemented for multi-threaded scenarios
cfg_if::cfg_if! {
if #[cfg(target_feature = "atomics")] {
// Access to the environment must be protected by a lock in multi-threaded scenarios.
use crate::sync::{PoisonError, RwLock};
static ENV_LOCK: RwLock<()> = RwLock::new(());
pub fn env_read_lock() -> impl Drop {
ENV_LOCK.read().unwrap_or_else(PoisonError::into_inner)
}
pub fn env_write_lock() -> impl Drop {
ENV_LOCK.write().unwrap_or_else(PoisonError::into_inner)
}
} else {
// No need for a lock if we are single-threaded.
pub fn env_read_lock() -> impl Drop {
()
}
pub fn env_write_lock() -> impl Drop {
()
}
}
}
@ -149,7 +160,7 @@ impl Iterator for Env {
pub fn env() -> Env {
unsafe {
let _guard = env_lock();
let _guard = env_read_lock();
let mut environ = libc::environ;
let mut result = Vec::new();
if !environ.is_null() {
@ -180,7 +191,7 @@ pub fn env() -> Env {
pub fn getenv(k: &OsStr) -> Option<OsString> {
let s = run_with_cstr(k.as_bytes(), |k| unsafe {
let _guard = env_lock();
let _guard = env_read_lock();
Ok(libc::getenv(k.as_ptr()) as *const libc::c_char)
})
.ok()?;
@ -194,7 +205,7 @@ pub fn getenv(k: &OsStr) -> Option<OsString> {
pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
run_with_cstr(k.as_bytes(), |k| {
run_with_cstr(v.as_bytes(), |v| unsafe {
let _guard = env_lock();
let _guard = env_write_lock();
cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
})
})
@ -202,7 +213,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
pub fn unsetenv(n: &OsStr) -> io::Result<()> {
run_with_cstr(n.as_bytes(), |nbuf| unsafe {
let _guard = env_lock();
let _guard = env_write_lock();
cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
})
}