Add wasm32-wasi-threads target + WASI threads

Author: g0djan

std/Cargo.toml

@@ -47,7 +47,7 @@ fortanix-sgx-abi = { version = "0.5.0", features = ['rustc-dep-of-std'], public
 [target.'cfg(target_os = "hermit")'.dependencies]
 hermit-abi = { version = "0.3.2", features = ['rustc-dep-of-std'], public = true }
 
-[target.wasm32-wasi.dependencies]
+[target.'cfg(target_os = "wasi")'.dependencies]
 wasi = { version = "0.11.0", features = ['rustc-dep-of-std'], default-features = false }
 
 [features]

std/src/sys/wasi/mod.rs

@@ -29,8 +29,7 @@ pub mod fs;
 #[path = "../wasm/atomics/futex.rs"]
 pub mod futex;
 pub mod io;
-#[path = "../unsupported/locks/mod.rs"]
-pub mod locks;
+
 pub mod net;
 pub mod os;
 #[path = "../unix/os_str.rs"]
@@ -47,14 +46,27 @@ pub mod thread;
 pub mod thread_local_dtor;
 #[path = "../unsupported/thread_local_key.rs"]
 pub mod thread_local_key;
-#[path = "../unsupported/thread_parking.rs"]
-pub mod thread_parking;
 pub mod time;
 
 cfg_if::cfg_if! {
-    if #[cfg(not(target_feature = "atomics"))] {
+    if #[cfg(target_feature = "atomics")] {
+        #[path = "../unix/locks"]
+        pub mod locks {
+            #![allow(unsafe_op_in_unsafe_fn)]
+            mod futex_condvar;
+            mod futex_mutex;
+            mod futex_rwlock;
+            pub(crate) use futex_condvar::Condvar;
+            pub(crate) use futex_mutex::Mutex;
+            pub(crate) use futex_rwlock::RwLock;
+        }
+    } else {
+        #[path = "../unsupported/locks/mod.rs"]
+        pub mod locks;
         #[path = "../unsupported/once.rs"]
         pub mod once;
+        #[path = "../unsupported/thread_parking.rs"]
+        pub mod thread_parking;
     }
 }
 

std/src/sys/wasi/os.rs

@@ -224,6 +224,11 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     })
 }
 
+#[allow(dead_code)]
+pub fn page_size() -> usize {
+    unsafe { libc::sysconf(libc::_SC_PAGESIZE) as usize }
+}
+
 pub fn temp_dir() -> PathBuf {
     panic!("no filesystem on wasm")
 }

std/src/sys/wasi/thread.rs

@@ -1,20 +1,120 @@
-#![deny(unsafe_op_in_unsafe_fn)]
-
 use crate::ffi::CStr;
 use crate::io;
 use crate::mem;
 use crate::num::NonZeroUsize;
 use crate::sys::unsupported;
 use crate::time::Duration;
 
-pub struct Thread(!);
+cfg_if::cfg_if! {
+    if #[cfg(target_feature = "atomics")] {
+        use crate::cmp;
+        use crate::ptr;
+        use crate::sys::os;
+        // Add a few symbols not in upstream `libc` just yet.
+        mod libc {
+            pub use crate::ffi;
+            pub use crate::mem;
+            pub use libc::*;
+
+            // defined in wasi-libc
+            // https://github.com/WebAssembly/wasi-libc/blob/a6f871343313220b76009827ed0153586361c0d5/libc-top-half/musl/include/alltypes.h.in#L108
+            #[repr(C)]
+            union pthread_attr_union {
+                __i: [ffi::c_int; if mem::size_of::<ffi::c_int>() == 8 { 14 } else { 9 }],
+                __vi: [ffi::c_int; if mem::size_of::<ffi::c_int>() == 8 { 14 } else { 9 }],
+                __s: [ffi::c_ulong; if mem::size_of::<ffi::c_int>() == 8 { 7 } else { 9 }],
+            }
+
+            #[repr(C)]
+            pub struct pthread_attr_t {
+                __u: pthread_attr_union,
+            }
+
+            #[allow(non_camel_case_types)]
+            pub type pthread_t = *mut ffi::c_void;
+
+            extern "C" {
+                pub fn pthread_create(
+                    native: *mut pthread_t,
+                    attr: *const pthread_attr_t,
+                    f: extern "C" fn(*mut ffi::c_void) -> *mut ffi::c_void,
+                    value: *mut ffi::c_void,
+                ) -> ffi::c_int;
+                pub fn pthread_join(native: pthread_t, value: *mut *mut ffi::c_void) -> ffi::c_int;
+                pub fn pthread_attr_init(attrp: *mut pthread_attr_t) -> ffi::c_int;
+                pub fn pthread_attr_setstacksize(
+                    attr: *mut pthread_attr_t,
+                    stack_size: libc::size_t,
+                ) -> ffi::c_int;
+                pub fn pthread_attr_destroy(attr: *mut pthread_attr_t) -> ffi::c_int;
+            }
+        }
+
+        pub struct Thread {
+            id: libc::pthread_t,
+        }
+    } else {
+        pub struct Thread(!);
+    }
+}
 
 pub const DEFAULT_MIN_STACK_SIZE: usize = 4096;
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
-        unsupported()
+    cfg_if::cfg_if! {
+        if #[cfg(target_feature = "atomics")] {
+            pub unsafe fn new(stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+                let p = Box::into_raw(Box::new(p));
+                let mut native: libc::pthread_t = mem::zeroed();
+                let mut attr: libc::pthread_attr_t = mem::zeroed();
+                assert_eq!(libc::pthread_attr_init(&mut attr), 0);
+
+                let stack_size = cmp::max(stack, DEFAULT_MIN_STACK_SIZE);
+
+                match libc::pthread_attr_setstacksize(&mut attr, stack_size) {
+                    0 => {}
+                    n => {
+                        assert_eq!(n, libc::EINVAL);
+                        // EINVAL means |stack_size| is either too small or not a
+                        // multiple of the system page size. Because it's definitely
+                        // >= PTHREAD_STACK_MIN, it must be an alignment issue.
+                        // Round up to the nearest page and try again.
+                        let page_size = os::page_size();
+                        let stack_size =
+                            (stack_size + page_size - 1) & (-(page_size as isize - 1) as usize - 1);
+                        assert_eq!(libc::pthread_attr_setstacksize(&mut attr, stack_size), 0);
+                    }
+                };
+
+                let ret = libc::pthread_create(&mut native, &attr, thread_start, p as *mut _);
+                // Note: if the thread creation fails and this assert fails, then p will
+                // be leaked. However, an alternative design could cause double-free
+                // which is clearly worse.
+                assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
+
+                return if ret != 0 {
+                    // The thread failed to start and as a result p was not consumed. Therefore, it is
+                    // safe to reconstruct the box so that it gets deallocated.
+                    drop(Box::from_raw(p));
+                    Err(io::Error::from_raw_os_error(ret))
+                } else {
+                    Ok(Thread { id: native })
+                };
+
+                extern "C" fn thread_start(main: *mut libc::c_void) -> *mut libc::c_void {
+                    unsafe {
+                        // Finally, let's run some code.
+                        Box::from_raw(main as *mut Box<dyn FnOnce()>)();
+                    }
+                    ptr::null_mut()
+                }
+            }
+        } else {
+            pub unsafe fn new(_stack: usize, _p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+                unsupported()
+            }
+        }
     }
 
     pub fn yield_now() {
@@ -62,7 +162,19 @@ impl Thread {
     }
 
     pub fn join(self) {
-        self.0
+        cfg_if::cfg_if! {
+            if #[cfg(target_feature = "atomics")] {
+                unsafe {
+                    let ret = libc::pthread_join(self.id, ptr::null_mut());
+                    mem::forget(self);
+                    if ret != 0 {
+                        rtabort!("failed to join thread: {}", io::Error::from_raw_os_error(ret));
+                    }
+                }
+            } else {
+                self.0
+            }
+        }
     }
 }