diff options
Diffstat (limited to 'library/std/src/sys/itron/thread.rs')
| -rw-r--r-- | library/std/src/sys/itron/thread.rs | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/library/std/src/sys/itron/thread.rs b/library/std/src/sys/itron/thread.rs index c2b36680872..535703be33f 100644 --- a/library/std/src/sys/itron/thread.rs +++ b/library/std/src/sys/itron/thread.rs @@ -119,7 +119,7 @@ impl Thread { let old_lifecycle = inner .lifecycle - .swap(LIFECYCLE_EXITED_OR_FINISHED_OR_JOIN_FINALIZE, Ordering::Release); + .swap(LIFECYCLE_EXITED_OR_FINISHED_OR_JOIN_FINALIZE, Ordering::AcqRel); match old_lifecycle { LIFECYCLE_DETACHED => { @@ -129,9 +129,9 @@ impl Thread { // In this case, `*p_inner`'s ownership has been moved to // us, and we are responsible for dropping it. The acquire - // ordering is not necessary because the parent thread made - // no memory access needing synchronization since the call - // to `acre_tsk`. + // ordering ensures that the swap operation that wrote + // `LIFECYCLE_DETACHED` happens-before `Box::from_raw( + // p_inner)`. // Safety: See above. let _ = unsafe { Box::from_raw(p_inner) }; @@ -151,6 +151,9 @@ impl Thread { // Since the parent might drop `*inner` and terminate us as // soon as it sees `JOIN_FINALIZE`, the release ordering // must be used in the above `swap` call. + // + // To make the task referred to by `parent_tid` visible, we + // must use the acquire ordering in the above `swap` call. // [JOINING → JOIN_FINALIZE] // Wake up the parent task. @@ -218,11 +221,15 @@ impl Thread { let current_task = current_task as usize; - match inner.lifecycle.swap(current_task, Ordering::Acquire) { + match inner.lifecycle.swap(current_task, Ordering::AcqRel) { LIFECYCLE_INIT => { // [INIT → JOINING] // The child task will transition the state to `JOIN_FINALIZE` // and wake us up. + // + // To make the task referred to by `current_task` visible from + // the child task's point of view, we must use the release + // ordering in the above `swap` call. loop { expect_success_aborting(unsafe { abi::slp_tsk() }, &"slp_tsk"); // To synchronize with the child task's memory accesses to @@ -267,15 +274,15 @@ impl Drop for Thread { let inner = unsafe { self.p_inner.as_ref() }; // Detach the thread. - match inner.lifecycle.swap(LIFECYCLE_DETACHED_OR_JOINED, Ordering::Acquire) { + match inner.lifecycle.swap(LIFECYCLE_DETACHED_OR_JOINED, Ordering::AcqRel) { LIFECYCLE_INIT => { // [INIT → DETACHED] // When the time comes, the child will figure out that no // one will ever join it. // The ownership of `*p_inner` is moved to the child thread. - // However, the release ordering is not necessary because we - // made no memory access needing synchronization since the call - // to `acre_tsk`. + // The release ordering ensures that the above swap operation on + // `lifecycle` happens-before the child thread's + // `Box::from_raw(p_inner)`. } LIFECYCLE_FINISHED => { // [FINISHED → JOINED] |