1 files changed, 79 insertions, 0 deletions
diff --git a/llvm/lib/Support/Windows/Jobserver.inc b/llvm/lib/Support/Windows/Jobserver.inc
new file mode 100644
index 0000000..79028ee
--- /dev/null
+++ b/llvm/lib/Support/Windows/Jobserver.inc
@@ -0,0 +1,79 @@
+//==- llvm/Support/Windows/Jobserver.inc - Windows Jobserver Impl -*- C++ -*-=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Windows-specific parts of the JobserverClient class.
+// On Windows, the jobserver is implemented using a named semaphore.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Windows/WindowsSupport.h"
+#include <atomic>
+#include <cassert>
+
+namespace llvm {
+/// The constructor for the Windows jobserver client. It attempts to open a
+/// handle to an existing named semaphore, the name of which is provided by
+/// GNU make in the --jobserver-auth argument. If the semaphore is opened
+/// successfully, the client is marked as initialized.
+JobserverClientImpl::JobserverClientImpl(const JobserverConfig &Config) {
+  Semaphore = (void *)::OpenSemaphoreA(SEMAPHORE_MODIFY_STATE | SYNCHRONIZE,
+                                       FALSE, Config.Path.c_str());
+  if (Semaphore != nullptr)
+    IsInitialized = true;
+}
+
+/// The destructor closes the handle to the semaphore, releasing the resource.
+JobserverClientImpl::~JobserverClientImpl() {
+  if (Semaphore != nullptr)
+    ::CloseHandle((HANDLE)Semaphore);
+}
+
+/// Tries to acquire a job slot. The first call always returns the implicit
+/// slot. Subsequent calls use a non-blocking wait on the semaphore
+/// (`WaitForSingleObject` with a timeout of 0). If the wait succeeds, the
+/// semaphore's count is decremented, and an explicit job slot is acquired.
+/// If the wait times out, it means no slots are available, and an invalid
+/// slot is returned.
+JobSlot JobserverClientImpl::tryAcquire() {
+  if (!IsInitialized)
+    return JobSlot();
+
+  // First, grant the implicit slot.
+  if (HasImplicitSlot.exchange(false, std::memory_order_acquire)) {
+    return JobSlot::createImplicit();
+  }
+
+  // Try to acquire a slot from the semaphore without blocking.
+  if (::WaitForSingleObject((HANDLE)Semaphore, 0) == WAIT_OBJECT_0) {
+    // The explicit token value is arbitrary on Windows, as the semaphore
+    // count is the real resource.
+    return JobSlot::createExplicit(1);
+  }
+
+  return JobSlot(); // Invalid slot
+}
+
+/// Releases a job slot back to the pool. If the slot is implicit, it simply
+/// resets a flag. For an explicit slot, it increments the semaphore's count
+/// by one using `ReleaseSemaphore`, making the slot available to other
+/// processes.
+void JobserverClientImpl::release(JobSlot Slot) {
+  if (!IsInitialized || !Slot.isValid())
+    return;
+
+  if (Slot.isImplicit()) {
+    [[maybe_unused]] bool was_already_released =
+        HasImplicitSlot.exchange(true, std::memory_order_release);
+    assert(!was_already_released && "Implicit slot released twice");
+    return;
+  }
+
+  // Release the slot by incrementing the semaphore count.
+  (void)::ReleaseSemaphore((HANDLE)Semaphore, 1, NULL);
+}
+} // namespace llvm