From 967a8567b827413a9ef7c21b82396ae76fc70f02 Mon Sep 17 00:00:00 2001
From: Radu Berinde <radu@cockroachlabs.com>
Date: Thu, 25 Sep 2025 12:54:02 -0700
Subject: [PATCH] cockroach: runtime: add CurrentP

Add a simple function that returns the index of the P the goroutine is
running on. This will be used for efficient sharding of data
structures.
---
 src/runtime/cockroach.go | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 src/runtime/cockroach.go

diff --git a/src/runtime/cockroach.go b/src/runtime/cockroach.go
new file mode 100644
index 00000000000000..5ff4399db75c33
--- /dev/null
+++ b/src/runtime/cockroach.go
@@ -0,0 +1,12 @@
+package runtime
+
+// CurrentP returns the index of the current P, between 0 and the current
+// GOMAXPROCS.
+//
+// This can only be used as a best-effort facility; there is no guarantee that
+// the goroutine still runs on the same P when this function returns.
+func CurrentP() int {
+	// Note: preemption is not possible in-between these loads (there are no
+	// preemption-safe points).
+	return int(getg().m.p.ptr().id)
+}