Implement safepointing of threads

runtime/vm/safepoint.cc

+// 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.
+
+#include "vm/safepoint.h"
+
+#include "vm/thread.h"
+#include "vm/thread_registry.h"
+
+namespace dart {
+
+SafepointOperationScope::SafepointOperationScope(Thread* T) : StackResource(T) {
+  ASSERT(T != NULL);
+  Isolate* I = T->isolate();
+  ASSERT(I != NULL);
+  ASSERT(T->no_safepoint_scope_depth() == 0);
+
+  SafepointHandler* handler = I->safepoint_handler();
+  ASSERT(handler != NULL);
+
+  // Signal all threads to get to a safepoint and wait for them to
+  // get to a safepoint.
+  handler->SafepointThreads(T);
+}
+
+
+SafepointOperationScope::~SafepointOperationScope() {
+  Thread* T = thread();
+  ASSERT(T != NULL);
+  Isolate* I = T->isolate();
+  ASSERT(I != NULL);
+
+  // Resume all threads which are blocked for the safepoint operation.
+  SafepointHandler* handler = I->safepoint_handler();
+  ASSERT(handler != NULL);
+  handler->ResumeThreads(T);
+}
+
+
+SafepointHandler::SafepointHandler(Isolate* isolate)
+    : isolate_(isolate),
+      safepoint_lock_(new Monitor()),
+      number_threads_not_at_safepoint_(0),
+      safepoint_in_progress_(false) {
+}
+
+
+SafepointHandler::~SafepointHandler() {
+  ASSERT(safepoint_in_progress_ == false);
+  delete safepoint_lock_;
+  safepoint_lock_ = NULL;
+  isolate_ = NULL;
+}
+
+
+void SafepointHandler::SafepointThreads(Thread* T) {
+  {
+    // First grab the threads list lock for this isolate
+    // and check if a safepoint is already in progress. This
+    // ensures that two threads do not start a safepoint operation
+    // at the same time.
+    MonitorLocker sl(threads_lock());
+
+    // Now check to see if a safepoint operation is already in progress
+    // for this isolate, block if an operation is in progress.
+    while (safepoint_in_progress()) {
+      sl.WaitWithSafepointCheck(T);
+    }
+
+    // Set safepoint in progress by this thread.
+    set_safepoint_in_progress(true);
+
+    // Go over the active thread list and ensure that all threads active
+    // in the isolate reach a safepoint.
+    Thread* current = isolate()->thread_registry()->active_list();
+    while (current != NULL) {
+      MonitorLocker tl(current->thread_lock());
+      if (current != T) {
+        uint32_t state = current->SetSafepointRequested(true);
+        if (!Thread::IsAtSafepoint(state)) {
+          // Thread is not already at a safepoint so try to
+          // get it to a safepoint and wait for it to check in.
+          if (current->IsMutatorThread()) {
+            ASSERT(T->isolate() != NULL);
+            T->isolate()->ScheduleInterrupts(Isolate::kVMInterrupt);
+          }
+          MonitorLocker sl(safepoint_lock_);
+          ++number_threads_not_at_safepoint_;
+        }
+      } else {
+        current->SetAtSafepoint(true);
+      }
+      current = current->next();
+    }
+  }
+  // Now wait for all threads that are not already at a safepoint to check-in.
+  {
+    MonitorLocker sl(safepoint_lock_);
+    while (number_threads_not_at_safepoint_ > 0) {
+      sl.Wait();
+    }
+  }
+}
+
+
+void SafepointHandler::ResumeThreads(Thread* T) {
+  // First resume all the threads which are blocked for the safepoint
+  // operation.
+  MonitorLocker sl(threads_lock());
+  Thread* current = isolate()->thread_registry()->active_list();
+  while (current != NULL) {
+    MonitorLocker tl(current->thread_lock());
+    if (current != T) {
+      uint32_t state = current->SetSafepointRequested(false);
+      if (Thread::IsBlockedForSafepoint(state)) {
+        tl.Notify();
+      }
+    } else {
+      current->SetAtSafepoint(false);
+    }
+    current = current->next();
+  }
+  // Now set the safepoint_in_progress_ flag to false and notify all threads
+  // that are waiting to enter the isolate or waiting to start another
+  // safepoint operation.
+  set_safepoint_in_progress(false);
+  sl.NotifyAll();
+}
+
+
+void SafepointHandler::EnterSafepointUsingLock(Thread* T) {
+  MonitorLocker tl(T->thread_lock());
+  T->SetAtSafepoint(true);
+  if (T->IsSafepointRequested()) {
+    MonitorLocker sl(safepoint_lock_);
+    ASSERT(number_threads_not_at_safepoint_ > 0);
+    number_threads_not_at_safepoint_ -= 1;
+    sl.Notify();
+  }
+}
+
+
+void SafepointHandler::ExitSafepointUsingLock(Thread* T) {
+  MonitorLocker tl(T->thread_lock());
+  ASSERT(T->IsAtSafepoint());
+  while (T->IsSafepointRequested()) {
+    T->SetBlockedForSafepoint(true);
+    tl.Wait();
+    T->SetBlockedForSafepoint(false);
+  }
+  T->SetAtSafepoint(false);
+}
+
+
+void SafepointHandler::BlockForSafepoint(Thread* T) {
+  MonitorLocker tl(T->thread_lock());
+  if (T->IsSafepointRequested()) {
+    T->SetAtSafepoint(true);
+    {
+      MonitorLocker sl(safepoint_lock_);
+      ASSERT(number_threads_not_at_safepoint_ > 0);
+      number_threads_not_at_safepoint_ -= 1;
+      sl.Notify();
+    }
+    while (T->IsSafepointRequested()) {
+      T->SetBlockedForSafepoint(true);
+      tl.Wait();
+      T->SetBlockedForSafepoint(false);
+    }
+    T->SetAtSafepoint(false);
+  }
+}
+
+}  // namespace dart