1 files changed, 110 insertions, 0 deletions
diff --git a/js/src/gc/GCLock.h b/js/src/gc/GCLock.h
new file mode 100644
index 0000000000..64c28ac544
--- /dev/null
+++ b/js/src/gc/GCLock.h
@@ -0,0 +1,110 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * GC-internal classes for acquiring and releasing the GC lock.
+ */
+
+#ifndef gc_GCLock_h
+#define gc_GCLock_h
+
+#include "vm/Runtime.h"
+
+namespace js {
+
+class AutoUnlockGC;
+
+/*
+ * RAII class that takes the GC lock while it is live.
+ *
+ * Usually functions will pass const references of this class.  However
+ * non-const references can be used to either temporarily release the lock by
+ * use of AutoUnlockGC or to start background allocation when the lock is
+ * released.
+ */
+class MOZ_RAII AutoLockGC {
+ public:
+  explicit AutoLockGC(gc::GCRuntime* gc) : gc(gc) { lock(); }
+  explicit AutoLockGC(JSRuntime* rt) : AutoLockGC(&rt->gc) {}
+
+  ~AutoLockGC() { lockGuard_.reset(); }
+
+  js::LockGuard<js::Mutex>& guard() { return lockGuard_.ref(); }
+
+ protected:
+  void lock() {
+    MOZ_ASSERT(lockGuard_.isNothing());
+    lockGuard_.emplace(gc->lock);
+  }
+
+  void unlock() {
+    MOZ_ASSERT(lockGuard_.isSome());
+    lockGuard_.reset();
+  }
+
+  gc::GCRuntime* const gc;
+
+ private:
+  mozilla::Maybe<js::LockGuard<js::Mutex>> lockGuard_;
+
+  AutoLockGC(const AutoLockGC&) = delete;
+  AutoLockGC& operator=(const AutoLockGC&) = delete;
+
+  friend class AutoUnlockGC;  // For lock/unlock.
+};
+
+/*
+ * Same as AutoLockGC except it can optionally start a background chunk
+ * allocation task when the lock is released.
+ */
+class MOZ_RAII AutoLockGCBgAlloc : public AutoLockGC {
+ public:
+  explicit AutoLockGCBgAlloc(gc::GCRuntime* gc) : AutoLockGC(gc) {}
+  explicit AutoLockGCBgAlloc(JSRuntime* rt) : AutoLockGCBgAlloc(&rt->gc) {}
+
+  ~AutoLockGCBgAlloc() {
+    unlock();
+
+    /*
+     * We have to do this after releasing the lock because it may acquire
+     * the helper lock which could cause lock inversion if we still held
+     * the GC lock.
+     */
+    if (startBgAlloc) {
+      gc->startBackgroundAllocTaskIfIdle();
+    }
+  }
+
+  /*
+   * This can be used to start a background allocation task (if one isn't
+   * already running) that allocates chunks and makes them available in the
+   * free chunks list.  This happens after the lock is released in order to
+   * avoid lock inversion.
+   */
+  void tryToStartBackgroundAllocation() { startBgAlloc = true; }
+
+ private:
+  // true if we should start a background chunk allocation task after the
+  // lock is released.
+  bool startBgAlloc = false;
+};
+
+class MOZ_RAII AutoUnlockGC {
+ public:
+  explicit AutoUnlockGC(AutoLockGC& lock) : lock(lock) { lock.unlock(); }
+
+  ~AutoUnlockGC() { lock.lock(); }
+
+ private:
+  AutoLockGC& lock;
+
+  AutoUnlockGC(const AutoUnlockGC&) = delete;
+  AutoUnlockGC& operator=(const AutoUnlockGC&) = delete;
+};
+
+}  // namespace js
+
+#endif /* gc_GCLock_h */