Rollup merge of #84687 - a1phyr:improve_rwlock, r=m-ou-se

Multiple improvements to RwLocks

This PR replicates #77147, #77380 and #84650 on RWLocks :
- Split `sys_common::RWLock` in `StaticRWLock` and `MovableRWLock`
- Unbox rwlocks on some platforms (Windows, Wasm and unsupported)
- Simplify `RwLock::into_inner`

Notes to reviewers :
- For each target, I copied `MovableMutex` to guess if `MovableRWLock` should be boxed.
- ~A comment says that `StaticMutex` is not re-entrant, I don't understand why and I don't know whether it applies to `StaticRWLock`.~

r? `@m-ou-se`

7 files changed, 17 insertions, 58 deletions

diff --git a/library/std/src/sys/hermit/rwlock.rs b/library/std/src/sys/hermit/rwlock.rs
index 06442e925f4..d2058180121 100644
--- a/library/std/src/sys/hermit/rwlock.rs
+++ b/library/std/src/sys/hermit/rwlock.rs
@@ -8,6 +8,8 @@ pub struct RWLock {
     state: UnsafeCell<State>,
 }
 
+pub type MovableRWLock = Box<RWLock>;
+
 enum State {
     Unlocked,
     Reading(usize),
diff --git a/library/std/src/sys/sgx/rwlock.rs b/library/std/src/sys/sgx/rwlock.rs
index 0c96e3fcddc..2d038b51896 100644
--- a/library/std/src/sys/sgx/rwlock.rs
+++ b/library/std/src/sys/sgx/rwlock.rs
@@ -13,6 +13,8 @@ pub struct RWLock {
     writer: SpinMutex<WaitVariable<bool>>,
 }
 
+pub type MovableRWLock = Box<RWLock>;
+
 // Check at compile time that RWLock size matches C definition (see test_c_rwlock_initializer below)
 //
 // # Safety
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index bbc4691d963..41ca9762390 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -20,8 +20,7 @@ use crate::str;
 use crate::sys::cvt;
 use crate::sys::fd;
 use crate::sys::memchr;
-use crate::sys::rwlock::{RWLockReadGuard, StaticRWLock};
-use crate::sys_common::mutex::{StaticMutex, StaticMutexGuard};
+use crate::sys_common::rwlock::{StaticRWLock, StaticRWLockReadGuard};
 use crate::vec;
 
 use libc::{c_char, c_int, c_void};
@@ -490,8 +489,8 @@ pub unsafe fn environ() -> *mut *const *const c_char {
 
 static ENV_LOCK: StaticRWLock = StaticRWLock::new();
 
-pub fn env_read_lock() -> RWLockReadGuard {
-    ENV_LOCK.read_with_guard()
+pub fn env_read_lock() -> StaticRWLockReadGuard {
+    ENV_LOCK.read()
 }
 
 /// Returns a vector of (variable, value) byte-vector pairs for all the
@@ -551,7 +550,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
     let v = CString::new(v.as_bytes())?;
 
     unsafe {
-        let _guard = ENV_LOCK.write_with_guard();
+        let _guard = ENV_LOCK.write();
         cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
     }
 }
@@ -560,7 +559,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     let nbuf = CString::new(n.as_bytes())?;
 
     unsafe {
-        let _guard = ENV_LOCK.write_with_guard();
+        let _guard = ENV_LOCK.write();
         cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
     }
 }
diff --git a/library/std/src/sys/unix/rwlock.rs b/library/std/src/sys/unix/rwlock.rs
index d97d9d712fc..b1faf12c226 100644
--- a/library/std/src/sys/unix/rwlock.rs
+++ b/library/std/src/sys/unix/rwlock.rs
@@ -7,6 +7,8 @@ pub struct RWLock {
     num_readers: AtomicUsize,
 }
 
+pub type MovableRWLock = Box<RWLock>;
+
 unsafe impl Send for RWLock {}
 unsafe impl Sync for RWLock {}
 
@@ -139,55 +141,3 @@ impl RWLock {
         }
     }
 }
-
-pub struct StaticRWLock(RWLock);
-
-impl StaticRWLock {
-    pub const fn new() -> StaticRWLock {
-        StaticRWLock(RWLock::new())
-    }
-
-    /// Acquires shared access to the underlying lock, blocking the current
-    /// thread to do so.
-    ///
-    /// The lock is automatically unlocked when the returned guard is dropped.
-    #[inline]
-    pub fn read_with_guard(&'static self) -> RWLockReadGuard {
-        // SAFETY: All methods require static references, therefore self
-        // cannot be moved between invocations.
-        unsafe {
-            self.0.read();
-        }
-        RWLockReadGuard(&self.0)
-    }
-
-    /// Acquires write access to the underlying lock, blocking the current thread
-    /// to do so.
-    ///
-    /// The lock is automatically unlocked when the returned guard is dropped.
-    #[inline]
-    pub fn write_with_guard(&'static self) -> RWLockWriteGuard {
-        // SAFETY: All methods require static references, therefore self
-        // cannot be moved between invocations.
-        unsafe {
-            self.0.write();
-        }
-        RWLockWriteGuard(&self.0)
-    }
-}
-
-pub struct RWLockReadGuard(&'static RWLock);
-
-impl Drop for RWLockReadGuard {
-    fn drop(&mut self) {
-        unsafe { self.0.read_unlock() }
-    }
-}
-
-pub struct RWLockWriteGuard(&'static RWLock);
-
-impl Drop for RWLockWriteGuard {
-    fn drop(&mut self) {
-        unsafe { self.0.write_unlock() }
-    }
-}
diff --git a/library/std/src/sys/unsupported/rwlock.rs b/library/std/src/sys/unsupported/rwlock.rs
index 6982b2b155f..8438adeb5b5 100644
--- a/library/std/src/sys/unsupported/rwlock.rs
+++ b/library/std/src/sys/unsupported/rwlock.rs
@@ -5,6 +5,8 @@ pub struct RWLock {
     mode: Cell<isize>,
 }
 
+pub type MovableRWLock = RWLock;
+
 unsafe impl Send for RWLock {}
 unsafe impl Sync for RWLock {} // no threads on this platform
 
diff --git a/library/std/src/sys/wasm/atomics/rwlock.rs b/library/std/src/sys/wasm/atomics/rwlock.rs
index 06442e925f4..64eaa2fc482 100644
--- a/library/std/src/sys/wasm/atomics/rwlock.rs
+++ b/library/std/src/sys/wasm/atomics/rwlock.rs
@@ -8,6 +8,8 @@ pub struct RWLock {
     state: UnsafeCell<State>,
 }
 
+pub type MovableRWLock = RWLock;
+
 enum State {
     Unlocked,
     Reading(usize),
diff --git a/library/std/src/sys/windows/rwlock.rs b/library/std/src/sys/windows/rwlock.rs
index a769326352c..b7a5b1e7acc 100644
--- a/library/std/src/sys/windows/rwlock.rs
+++ b/library/std/src/sys/windows/rwlock.rs
@@ -5,6 +5,8 @@ pub struct RWLock {
     inner: UnsafeCell<c::SRWLOCK>,
 }
 
+pub type MovableRWLock = RWLock;
+
 unsafe impl Send for RWLock {}
 unsafe impl Sync for RWLock {}