[libc] Move fences into outbox/wait-for-ownership test
Also moves the wait-until-inbox-changes test into a shared method.
Reviewed By: jhuber6
Differential Revision: https://reviews.llvm.org/D153573
diff --git a/libc/src/__support/RPC/rpc.h b/libc/src/__support/RPC/rpc.h
index 98555da..c96468a 100644
--- a/libc/src/__support/RPC/rpc.h
+++ b/libc/src/__support/RPC/rpc.h
@@ -137,10 +137,22 @@
/// cheaper than calling load_outbox to get the value to store.
LIBC_INLINE uint32_t invert_outbox(uint64_t index, uint32_t current_outbox) {
uint32_t inverted_outbox = !current_outbox;
+ atomic_thread_fence(cpp::MemoryOrder::RELEASE);
outbox[index].store(inverted_outbox, cpp::MemoryOrder::RELAXED);
return inverted_outbox;
}
+ // Given the current outbox and inbox values, wait until the inbox changes
+ // to indicate that this thread owns the buffer element.
+ LIBC_INLINE void wait_for_ownership(uint64_t index, uint32_t outbox,
+ uint32_t in) {
+ while (buffer_unavailable(in, outbox)) {
+ sleep_briefly();
+ in = load_inbox(index);
+ }
+ atomic_thread_fence(cpp::MemoryOrder::ACQUIRE);
+ }
+
/// Determines if this process needs to wait for ownership of the buffer. We
/// invert the condition on one of the processes to indicate that if one
/// process owns the buffer then the other does not.
@@ -347,14 +359,10 @@
uint32_t in = owns_buffer ? out ^ T : process.load_inbox(index);
// We need to wait until we own the buffer before sending.
- while (Process<T, S>::buffer_unavailable(in, out)) {
- sleep_briefly();
- in = process.load_inbox(index);
- }
+ process.wait_for_ownership(index, out, in);
// Apply the \p fill function to initialize the buffer and release the memory.
process.invoke_rpc(fill, process.packet[index]);
- atomic_thread_fence(cpp::MemoryOrder::RELEASE);
out = process.invert_outbox(index, out);
owns_buffer = false;
receive = false;
@@ -374,11 +382,7 @@
uint32_t in = owns_buffer ? out ^ T : process.load_inbox(index);
// We need to wait until we own the buffer before receiving.
- while (Process<T, S>::buffer_unavailable(in, out)) {
- sleep_briefly();
- in = process.load_inbox(index);
- }
- atomic_thread_fence(cpp::MemoryOrder::ACQUIRE);
+ process.wait_for_ownership(index, out, in);
// Apply the \p use function to read the memory out of the buffer.
process.invoke_rpc(use, process.packet[index]);
