Implement safepointing of threads

runtime/vm/safepoint.h

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_SAFEPOINT_H_
+#define VM_SAFEPOINT_H_
+
+#include "vm/globals.h"
+#include "vm/lockers.h"
+#include "vm/thread.h"
+
+namespace dart {
+
+// A stack based scope that can be used to perform an operation after getting
+// all threads to a safepoint. At the end of the operation all the threads are
+// resumed.
+class SafepointOperationScope : public StackResource {
+ public:
+  explicit SafepointOperationScope(Thread* T);
+  ~SafepointOperationScope();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SafepointOperationScope);
+};
+
+
+// Implements handling of safepoint operations for all threads in an Isolate.
+class SafepointHandler {
+ public:
+  explicit SafepointHandler(Isolate* I);
+  ~SafepointHandler();
+
+  void EnterSafepointUsingLock(Thread* T);
+  void ExitSafepointUsingLock(Thread* T);
+
+  void SafepointThreads(Thread* T);
+  void ResumeThreads(Thread* T);
+
+  void BlockForSafepoint(Thread* T);
+
+ private:
+  Isolate* isolate() const { return isolate_; }
+  Monitor* threads_lock() const { return isolate_->threads_lock(); }
+  bool safepoint_in_progress() const {
+    ASSERT(threads_lock()->IsOwnedByCurrentThread());
+    return safepoint_in_progress_;
+  }
+  void set_safepoint_in_progress(bool value) {
+    ASSERT(threads_lock()->IsOwnedByCurrentThread());
+    safepoint_in_progress_ = value;
+  }
+
+  Isolate* isolate_;
+
+  // Monitor used by thread initiating a safepoint operation to track threads
+  // not at a safepoint and wait for these threads to reach a safepoint.
+  Monitor* safepoint_lock_;
+  int32_t number_threads_not_at_safepoint_;
+
+  // Flag to indicate if a safepoint operation is currently in progress.
+  bool safepoint_in_progress_;
+
+  friend class Isolate;
+  friend class SafepointOperationScope;
+};
+
+
+/*
+ * Set of StackResource classes to track thread execution state transitions:
+ *
+ * kThreadInGenerated transitioning to
+ *   ==> kThreadInVM:
+ *       - set_execution_state(kThreadInVM).
+ *       - block if safepoint is requested.
+ *   ==> kThreadInNative:
+ *       - set_execution_state(kThreadInNative).
+ *       - EnterSafepoint().
+ *   ==> kThreadInBlockedState:
+ *       - Invalid transition
+ *
+ * kThreadInVM transitioning to
+ *   ==> kThreadInGenerated
+ *       - set_execution_state(kThreadInGenerated).
+ *   ==> kThreadInNative
+ *       - set_execution_state(kThreadInNative).
+ *       - EnterSafepoint.
+ *   ==> kThreadInBlockedState
+ *       - set_execution_state(kThreadInBlockedState).
+ *       - EnterSafepoint.
+ *
+ * kThreadInNative transitioning to
+ *   ==> kThreadInGenerated
+ *       - ExitSafepoint.
+ *       - set_execution_state(kThreadInGenerated).
+ *   ==> kThreadInVM
+ *       - ExitSafepoint.
+ *       - set_execution_state(kThreadInVM).
+ *   ==> kThreadInBlocked
+ *       - Invalid transition.
+ *
+ * kThreadInBlocked transitioning to
+ *   ==> kThreadInVM
+ *       - ExitSafepoint.
+ *       - set_execution_state(kThreadInVM).
+ *   ==> kThreadInNative
+ *       - Invalid transition.
+ *   ==> kThreadInGenerated
+ *       - Invalid transition.
+ */
+class TransitionSafepointState : public StackResource {
+ public:
+  explicit TransitionSafepointState(Thread* T) : StackResource(T) {}
+  ~TransitionSafepointState() {}
+
+  SafepointHandler* handler() const {
+    ASSERT(thread()->isolate() != NULL);
+    ASSERT(thread()->isolate()->safepoint_handler() != NULL);
+    return thread()->isolate()->safepoint_handler();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionSafepointState);
+};
+
+
+// TransitionGeneratedToVM is used to transition the safepoint state of a
+// thread from "running generated code" to "running vm code" and ensures
+// that the state is reverted back to "running generated code" when
+// exiting the scope/frame.
+class TransitionGeneratedToVM : public TransitionSafepointState {
+ public:
+  explicit TransitionGeneratedToVM(Thread* T) : TransitionSafepointState(T) {
+    ASSERT(T == Thread::Current());
+    ASSERT(T->execution_state() == Thread::kThreadInGenerated);
+    T->set_execution_state(Thread::kThreadInVM);
+    // Fast check to see if a safepoint is requested or not.
+    // We do the more expensive operation of blocking the thread
+    // only if a safepoint is requested.
+    if (T->IsSafepointRequested()) {
+      handler()->BlockForSafepoint(T);
+    }
+  }
+
+  ~TransitionGeneratedToVM() {
+    ASSERT(thread()->execution_state() == Thread::kThreadInVM);
+    thread()->set_execution_state(Thread::kThreadInGenerated);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionGeneratedToVM);
+};
+
+
+// TransitionGeneratedToNative is used to transition the safepoint state of a
+// thread from "running generated code" to "running native code" and ensures
+// that the state is reverted back to "running generated code" when
+// exiting the scope/frame.
+class TransitionGeneratedToNative : public TransitionSafepointState {
+ public:
+  explicit TransitionGeneratedToNative(Thread* T)
+      : TransitionSafepointState(T) {
+    // Native code is considered to be at a safepoint and so we mark it
+    // accordingly.
+    ASSERT(T->execution_state() == Thread::kThreadInGenerated);
+    T->set_execution_state(Thread::kThreadInNative);
+    T->EnterSafepoint();
+  }
+
+  ~TransitionGeneratedToNative() {
+    // We are returning to generated code and so we are not at a safepoint
+    // anymore.
+    ASSERT(thread()->execution_state() == Thread::kThreadInNative);
+    thread()->ExitSafepoint();
+    thread()->set_execution_state(Thread::kThreadInGenerated);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionGeneratedToNative);
+};
+
+
+// TransitionVMToBlocked is used to transition the safepoint state of a
+// thread from "running vm code" to "blocked on a monitor" and ensures
+// that the state is reverted back to "running vm code" when
+// exiting the scope/frame.
+class TransitionVMToBlocked : public TransitionSafepointState {
+ public:
+  explicit TransitionVMToBlocked(Thread* T) : TransitionSafepointState(T) {
+    // A thread blocked on a monitor is considered to be at a safepoint.
+    ASSERT(T->execution_state() == Thread::kThreadInVM);
+    T->set_execution_state(Thread::kThreadInBlockedState);
+    T->EnterSafepoint();
+  }
+
+  ~TransitionVMToBlocked() {
+    // We are returning to vm code and so we are not at a safepoint anymore.
+    ASSERT(thread()->execution_state() == Thread::kThreadInBlockedState);
+    thread()->ExitSafepoint();
+    thread()->set_execution_state(Thread::kThreadInVM);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionVMToBlocked);
+};
+
+
+// TransitionVMToNative is used to transition the safepoint state of a
+// thread from "running vm code" to "running native code" and ensures
+// that the state is reverted back to "running vm code" when
+// exiting the scope/frame.
+class TransitionVMToNative : public TransitionSafepointState {
+ public:
+  explicit TransitionVMToNative(Thread* T) : TransitionSafepointState(T) {
+    // A thread running native code is considered to be at a safepoint.
+    ASSERT(T->execution_state() == Thread::kThreadInVM);
+    T->set_execution_state(Thread::kThreadInNative);
+    T->EnterSafepoint();
+  }
+
+  ~TransitionVMToNative() {
+    // We are returning to vm code and so we are not at a safepoint anymore.
+    ASSERT(thread()->execution_state() == Thread::kThreadInNative);
+    thread()->ExitSafepoint();
+    thread()->set_execution_state(Thread::kThreadInVM);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionVMToNative);
+};
+
+
+// TransitionVMToGenerated is used to transition the safepoint state of a
+// thread from "running vm code" to "running generated code" and ensures
+// that the state is reverted back to "running vm code" when
+// exiting the scope/frame.
+class TransitionVMToGenerated : public TransitionSafepointState {
+ public:
+  explicit TransitionVMToGenerated(Thread* T) : TransitionSafepointState(T) {
+    ASSERT(T == Thread::Current());
+    ASSERT(T->execution_state() == Thread::kThreadInVM);
+    T->set_execution_state(Thread::kThreadInGenerated);
+  }
+
+  ~TransitionVMToGenerated() {
+    ASSERT(thread()->execution_state() == Thread::kThreadInGenerated);
+    thread()->set_execution_state(Thread::kThreadInVM);
+    // Fast check to see if a safepoint is requested or not.
+    // We do the more expensive operation of blocking the thread
+    // only if a safepoint is requested.
+    if (thread()->IsSafepointRequested()) {
+      handler()->BlockForSafepoint(thread());
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionVMToGenerated);
+};
+
+
+// TransitionNativeToVM is used to transition the safepoint state of a
+// thread from "running native code" to "running vm code" and ensures
+// that the state is reverted back to "running native code" when
+// exiting the scope/frame.
+class TransitionNativeToVM : public TransitionSafepointState {
+ public:
+  explicit TransitionNativeToVM(Thread* T) : TransitionSafepointState(T) {
+    // We are about to execute vm code and so we are not at a safepoint anymore.
+    ASSERT(T->execution_state() == Thread::kThreadInNative);
+    T->ExitSafepoint();
+    T->set_execution_state(Thread::kThreadInVM);
+  }
+
+  ~TransitionNativeToVM() {
+    // We are returning to native code and so we are at a safepoint.
+    ASSERT(thread()->execution_state() == Thread::kThreadInVM);
+    thread()->set_execution_state(Thread::kThreadInNative);
+    thread()->EnterSafepoint();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionNativeToVM);
+};
+
+
+// TransitionToGenerated is used to transition the safepoint state of a
+// thread from "running vm code" or "running native code" to
+// "running generated code" and ensures that the state is reverted back
+// to "running vm code" or "running native code" when exiting the
+// scope/frame.
+class TransitionToGenerated : public TransitionSafepointState {
+ public:
+  explicit TransitionToGenerated(Thread* T)
+      : TransitionSafepointState(T),
+        execution_state_(T->execution_state()) {
+    ASSERT(T == Thread::Current());
+    ASSERT((execution_state_ == Thread::kThreadInVM) ||
+           (execution_state_ == Thread::kThreadInNative));
+    if (execution_state_ == Thread::kThreadInNative) {
+      T->ExitSafepoint();
+    }
+    T->set_execution_state(Thread::kThreadInGenerated);
+  }
+
+  ~TransitionToGenerated() {
+    ASSERT(thread()->execution_state() == Thread::kThreadInGenerated);
+    if (execution_state_ == Thread::kThreadInNative) {
+      thread()->set_execution_state(Thread::kThreadInNative);
+      thread()->EnterSafepoint();
+    } else {
+      ASSERT(execution_state_ == Thread::kThreadInVM);
+      thread()->set_execution_state(Thread::kThreadInVM);
+      // Fast check to see if a safepoint is requested or not.
+      // We do the more expensive operation of blocking the thread
+      // only if a safepoint is requested.
+      if (thread()->IsSafepointRequested()) {
+        handler()->BlockForSafepoint(thread());
+      }
+    }
+  }
+
+ private:
+  int16_t execution_state_;
+  DISALLOW_COPY_AND_ASSIGN(TransitionToGenerated);
+};
+
+}  // namespace dart
+
+#endif  // VM_SAFEPOINT_H_