1 files changed, 467 insertions, 0 deletions
diff --git a/ipc/glue/IdleSchedulerParent.cpp b/ipc/glue/IdleSchedulerParent.cpp
new file mode 100644
index 0000000000..c5cf0b3b20
--- /dev/null
+++ b/ipc/glue/IdleSchedulerParent.cpp
@@ -0,0 +1,467 @@
+/* -*- 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/. */
+
+#include "mozilla/StaticPrefs_page_load.h"
+#include "mozilla/StaticPrefs_javascript.h"
+#include "mozilla/Unused.h"
+#include "mozilla/ipc/IdleSchedulerParent.h"
+#include "mozilla/AppShutdown.h"
+#include "mozilla/Telemetry.h"
+#include "nsSystemInfo.h"
+#include "nsThreadUtils.h"
+#include "nsITimer.h"
+#include "nsIThread.h"
+
+namespace mozilla::ipc {
+
+base::SharedMemory* IdleSchedulerParent::sActiveChildCounter = nullptr;
+std::bitset<NS_IDLE_SCHEDULER_COUNTER_ARRAY_LENGHT>
+    IdleSchedulerParent::sInUseChildCounters;
+LinkedList<IdleSchedulerParent> IdleSchedulerParent::sIdleAndGCRequests;
+int32_t IdleSchedulerParent::sMaxConcurrentIdleTasksInChildProcesses = 1;
+uint32_t IdleSchedulerParent::sMaxConcurrentGCs = 1;
+uint32_t IdleSchedulerParent::sActiveGCs = 0;
+bool IdleSchedulerParent::sRecordGCTelemetry = false;
+uint32_t IdleSchedulerParent::sNumWaitingGC = 0;
+uint32_t IdleSchedulerParent::sChildProcessesRunningPrioritizedOperation = 0;
+uint32_t IdleSchedulerParent::sChildProcessesAlive = 0;
+nsITimer* IdleSchedulerParent::sStarvationPreventer = nullptr;
+
+uint32_t IdleSchedulerParent::sNumCPUs = 0;
+uint32_t IdleSchedulerParent::sPrefConcurrentGCsMax = 0;
+uint32_t IdleSchedulerParent::sPrefConcurrentGCsCPUDivisor = 0;
+
+IdleSchedulerParent::IdleSchedulerParent() {
+  MOZ_ASSERT(!AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownThreads));
+
+  sChildProcessesAlive++;
+
+  uint32_t max_gcs_pref =
+      StaticPrefs::javascript_options_concurrent_multiprocess_gcs_max();
+  uint32_t cpu_divisor_pref =
+      StaticPrefs::javascript_options_concurrent_multiprocess_gcs_cpu_divisor();
+  if (!max_gcs_pref) {
+    max_gcs_pref = UINT32_MAX;
+  }
+  if (!cpu_divisor_pref) {
+    cpu_divisor_pref = 4;
+  }
+
+  if (!sNumCPUs) {
+    // While waiting for the real logical core count behave as if there was
+    // just one core.
+    sNumCPUs = 1;
+
+    // nsISystemInfo can be initialized only on the main thread.
+    nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
+    nsCOMPtr<nsIRunnable> runnable =
+        NS_NewRunnableFunction("cpucount getter", [thread]() {
+          ProcessInfo processInfo = {};
+          if (NS_SUCCEEDED(CollectProcessInfo(processInfo))) {
+            uint32_t num_cpus = processInfo.cpuCount;
+            // We have a new cpu count, Update the number of idle tasks.
+            if (MOZ_LIKELY(!AppShutdown::IsInOrBeyond(
+                    ShutdownPhase::XPCOMShutdownThreads))) {
+              nsCOMPtr<nsIRunnable> runnable = NS_NewRunnableFunction(
+                  "IdleSchedulerParent::CalculateNumIdleTasks", [num_cpus]() {
+                    // We're setting this within this lambda because it's run on
+                    // the correct thread and avoids a race.
+                    sNumCPUs = num_cpus;
+
+                    // This reads the sPrefConcurrentGCsMax and
+                    // sPrefConcurrentGCsCPUDivisor values set below, it will
+                    // run after the code that sets those.
+                    CalculateNumIdleTasks();
+                  });
+
+              thread->Dispatch(runnable, NS_DISPATCH_NORMAL);
+            }
+          }
+        });
+    NS_DispatchBackgroundTask(runnable.forget(), NS_DISPATCH_EVENT_MAY_BLOCK);
+  }
+
+  if (sPrefConcurrentGCsMax != max_gcs_pref ||
+      sPrefConcurrentGCsCPUDivisor != cpu_divisor_pref) {
+    // We execute this if these preferences have changed. We also want to make
+    // sure it executes for the first IdleSchedulerParent, which it does because
+    // sPrefConcurrentGCsMax and sPrefConcurrentGCsCPUDivisor are initially
+    // zero.
+    sPrefConcurrentGCsMax = max_gcs_pref;
+    sPrefConcurrentGCsCPUDivisor = cpu_divisor_pref;
+
+    CalculateNumIdleTasks();
+  }
+}
+
+void IdleSchedulerParent::CalculateNumIdleTasks() {
+  MOZ_ASSERT(sNumCPUs);
+  MOZ_ASSERT(sPrefConcurrentGCsMax);
+  MOZ_ASSERT(sPrefConcurrentGCsCPUDivisor);
+
+  // On one and two processor (or hardware thread) systems this will
+  // allow one concurrent idle task.
+  sMaxConcurrentIdleTasksInChildProcesses = int32_t(std::max(sNumCPUs, 1u));
+  sMaxConcurrentGCs =
+      std::min(std::max(sNumCPUs / sPrefConcurrentGCsCPUDivisor, 1u),
+               sPrefConcurrentGCsMax);
+
+  if (sActiveChildCounter && sActiveChildCounter->memory()) {
+    static_cast<Atomic<int32_t>*>(
+        sActiveChildCounter->memory())[NS_IDLE_SCHEDULER_INDEX_OF_CPU_COUNTER] =
+        static_cast<int32_t>(sMaxConcurrentIdleTasksInChildProcesses);
+  }
+  IdleSchedulerParent::Schedule(nullptr);
+}
+
+IdleSchedulerParent::~IdleSchedulerParent() {
+  // We can't know if an active process just crashed, so we just always expect
+  // that is the case.
+  if (mChildId) {
+    sInUseChildCounters[mChildId] = false;
+    if (sActiveChildCounter && sActiveChildCounter->memory() &&
+        static_cast<Atomic<int32_t>*>(
+            sActiveChildCounter->memory())[mChildId]) {
+      --static_cast<Atomic<int32_t>*>(
+          sActiveChildCounter
+              ->memory())[NS_IDLE_SCHEDULER_INDEX_OF_ACTIVITY_COUNTER];
+      static_cast<Atomic<int32_t>*>(sActiveChildCounter->memory())[mChildId] =
+          0;
+    }
+  }
+
+  if (mRunningPrioritizedOperation) {
+    --sChildProcessesRunningPrioritizedOperation;
+  }
+
+  if (mDoingGC) {
+    // Give back our GC token.
+    sActiveGCs--;
+  }
+
+  if (mRequestingGC) {
+    mRequestingGC.value()(false);
+    mRequestingGC = Nothing();
+  }
+
+  // Remove from the scheduler's queue.
+  if (isInList()) {
+    remove();
+  }
+
+  MOZ_ASSERT(sChildProcessesAlive > 0);
+  sChildProcessesAlive--;
+  if (sChildProcessesAlive == 0) {
+    MOZ_ASSERT(sIdleAndGCRequests.isEmpty());
+    delete sActiveChildCounter;
+    sActiveChildCounter = nullptr;
+
+    if (sStarvationPreventer) {
+      sStarvationPreventer->Cancel();
+      NS_RELEASE(sStarvationPreventer);
+    }
+  }
+
+  Schedule(nullptr);
+}
+
+IPCResult IdleSchedulerParent::RecvInitForIdleUse(
+    InitForIdleUseResolver&& aResolve) {
+  // This must already be non-zero, if it is zero then the cleanup code for the
+  // shared memory (initialised below) will never run.  The invariant is that if
+  // the shared memory is initialsed, then this is non-zero.
+  MOZ_ASSERT(sChildProcessesAlive > 0);
+
+  MOZ_ASSERT(IsNotDoingIdleTask());
+
+  // Create a shared memory object which is shared across all the relevant
+  // processes.
+  if (!sActiveChildCounter) {
+    sActiveChildCounter = new base::SharedMemory();
+    size_t shmemSize = NS_IDLE_SCHEDULER_COUNTER_ARRAY_LENGHT * sizeof(int32_t);
+    if (sActiveChildCounter->Create(shmemSize) &&
+        sActiveChildCounter->Map(shmemSize)) {
+      memset(sActiveChildCounter->memory(), 0, shmemSize);
+      sInUseChildCounters[NS_IDLE_SCHEDULER_INDEX_OF_ACTIVITY_COUNTER] = true;
+      sInUseChildCounters[NS_IDLE_SCHEDULER_INDEX_OF_CPU_COUNTER] = true;
+      static_cast<Atomic<int32_t>*>(
+          sActiveChildCounter
+              ->memory())[NS_IDLE_SCHEDULER_INDEX_OF_CPU_COUNTER] =
+          static_cast<int32_t>(sMaxConcurrentIdleTasksInChildProcesses);
+    } else {
+      delete sActiveChildCounter;
+      sActiveChildCounter = nullptr;
+    }
+  }
+  Maybe<SharedMemoryHandle> activeCounter;
+  if (SharedMemoryHandle handle =
+          sActiveChildCounter ? sActiveChildCounter->CloneHandle() : nullptr) {
+    activeCounter.emplace(std::move(handle));
+  }
+
+  uint32_t unusedId = 0;
+  for (uint32_t i = 0; i < NS_IDLE_SCHEDULER_COUNTER_ARRAY_LENGHT; ++i) {
+    if (!sInUseChildCounters[i]) {
+      sInUseChildCounters[i] = true;
+      unusedId = i;
+      break;
+    }
+  }
+
+  // If there wasn't an empty item, we'll fallback to 0.
+  mChildId = unusedId;
+
+  aResolve(std::tuple<mozilla::Maybe<SharedMemoryHandle>&&, const uint32_t&>(
+      std::move(activeCounter), mChildId));
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvRequestIdleTime(uint64_t aId,
+                                                   TimeDuration aBudget) {
+  MOZ_ASSERT(aBudget);
+  MOZ_ASSERT(IsNotDoingIdleTask());
+
+  mCurrentRequestId = aId;
+  mRequestedIdleBudget = aBudget;
+
+  if (!isInList()) {
+    sIdleAndGCRequests.insertBack(this);
+  }
+
+  Schedule(this);
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvIdleTimeUsed(uint64_t aId) {
+  // The client can either signal that they've used the idle time or they're
+  // canceling the request.  We cannot use a seperate cancel message because it
+  // could arrive after the parent has granted the request.
+  MOZ_ASSERT(IsWaitingForIdle() || IsDoingIdleTask());
+
+  // The parent process will always know the ID of the current request (since
+  // the IPC channel is reliable).  The IDs are provided so that the client can
+  // check them (it's possible for the client to race ahead of the server).
+  MOZ_ASSERT(mCurrentRequestId == aId);
+
+  if (IsWaitingForIdle() && !mRequestingGC) {
+    remove();
+  }
+  mRequestedIdleBudget = TimeDuration();
+  Schedule(nullptr);
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvSchedule() {
+  Schedule(nullptr);
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvRunningPrioritizedOperation() {
+  ++mRunningPrioritizedOperation;
+  if (mRunningPrioritizedOperation == 1) {
+    ++sChildProcessesRunningPrioritizedOperation;
+  }
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvPrioritizedOperationDone() {
+  MOZ_ASSERT(mRunningPrioritizedOperation);
+
+  --mRunningPrioritizedOperation;
+  if (mRunningPrioritizedOperation == 0) {
+    --sChildProcessesRunningPrioritizedOperation;
+    Schedule(nullptr);
+  }
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvRequestGC(RequestGCResolver&& aResolver) {
+  MOZ_ASSERT(!mDoingGC);
+  MOZ_ASSERT(!mRequestingGC);
+
+  mRequestingGC = Some(aResolver);
+  if (!isInList()) {
+    sIdleAndGCRequests.insertBack(this);
+  }
+
+  sRecordGCTelemetry = true;
+  sNumWaitingGC++;
+  Schedule(nullptr);
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvStartedGC() {
+  if (mDoingGC) {
+    return IPC_OK();
+  }
+
+  mDoingGC = true;
+  sActiveGCs++;
+
+  if (mRequestingGC) {
+    sNumWaitingGC--;
+    // We have to respond to the request before dropping it, even though the
+    // content process is already doing the GC.
+    mRequestingGC.value()(true);
+    mRequestingGC = Nothing();
+    if (!IsWaitingForIdle()) {
+      remove();
+    }
+    sRecordGCTelemetry = true;
+  }
+
+  return IPC_OK();
+}
+
+IPCResult IdleSchedulerParent::RecvDoneGC() {
+  MOZ_ASSERT(mDoingGC);
+  sActiveGCs--;
+  mDoingGC = false;
+  sRecordGCTelemetry = true;
+  Schedule(nullptr);
+  return IPC_OK();
+}
+
+int32_t IdleSchedulerParent::ActiveCount() {
+  if (sActiveChildCounter) {
+    return (static_cast<Atomic<int32_t>*>(
+        sActiveChildCounter
+            ->memory())[NS_IDLE_SCHEDULER_INDEX_OF_ACTIVITY_COUNTER]);
+  }
+  return 0;
+}
+
+bool IdleSchedulerParent::HasSpareCycles(int32_t aActiveCount) {
+  // We can run a new task if we have a spare core.  If we're running a
+  // prioritised operation we halve the number of regular spare cores.
+  //
+  // sMaxConcurrentIdleTasksInChildProcesses will always be >0 so on 1 and 2
+  // core systems this will allow 1 idle tasks (0 if running a prioritized
+  // operation).
+  MOZ_ASSERT(sMaxConcurrentIdleTasksInChildProcesses > 0);
+  return sChildProcessesRunningPrioritizedOperation
+             ? sMaxConcurrentIdleTasksInChildProcesses / 2 > aActiveCount
+             : sMaxConcurrentIdleTasksInChildProcesses > aActiveCount;
+}
+
+bool IdleSchedulerParent::HasSpareGCCycles() {
+  return sMaxConcurrentGCs > sActiveGCs;
+}
+
+void IdleSchedulerParent::SendIdleTime() {
+  // We would assert that IsWaitingForIdle() except after potentially removing
+  // the task from it's list this will return false.  Instead check
+  // mRequestedIdleBudget.
+  MOZ_ASSERT(mRequestedIdleBudget);
+  Unused << SendIdleTime(mCurrentRequestId, mRequestedIdleBudget);
+}
+
+void IdleSchedulerParent::SendMayGC() {
+  MOZ_ASSERT(mRequestingGC);
+  mRequestingGC.value()(true);
+  mRequestingGC = Nothing();
+  mDoingGC = true;
+  sActiveGCs++;
+  sRecordGCTelemetry = true;
+  MOZ_ASSERT(sNumWaitingGC > 0);
+  sNumWaitingGC--;
+}
+
+void IdleSchedulerParent::Schedule(IdleSchedulerParent* aRequester) {
+  // Tasks won't update the active count until after they receive their message
+  // and start to run, so make a copy of it here and increment it for every task
+  // we schedule. It will become an estimate of how many tasks will be active
+  // shortly.
+  int32_t activeCount = ActiveCount();
+
+  if (aRequester && aRequester->mRunningPrioritizedOperation) {
+    // Prioritised operations are requested only for idle time requests, so this
+    // must be an idle time request.
+    MOZ_ASSERT(aRequester->IsWaitingForIdle());
+
+    // If the requester is prioritized, just let it run itself.
+    if (aRequester->isInList() && !aRequester->mRequestingGC) {
+      aRequester->remove();
+    }
+    aRequester->SendIdleTime();
+    activeCount++;
+  }
+
+  RefPtr<IdleSchedulerParent> idleRequester = sIdleAndGCRequests.getFirst();
+
+  bool has_spare_cycles = HasSpareCycles(activeCount);
+  bool has_spare_gc_cycles = HasSpareGCCycles();
+
+  while (idleRequester && (has_spare_cycles || has_spare_gc_cycles)) {
+    // Get the next element before potentially removing the current one from the
+    // list.
+    RefPtr<IdleSchedulerParent> next = idleRequester->getNext();
+
+    if (has_spare_cycles && idleRequester->IsWaitingForIdle()) {
+      // We can run an idle task.
+      activeCount++;
+      if (!idleRequester->mRequestingGC) {
+        idleRequester->remove();
+      }
+      idleRequester->SendIdleTime();
+      has_spare_cycles = HasSpareCycles(activeCount);
+    }
+
+    if (has_spare_gc_cycles && idleRequester->mRequestingGC) {
+      if (!idleRequester->IsWaitingForIdle()) {
+        idleRequester->remove();
+      }
+      idleRequester->SendMayGC();
+      has_spare_gc_cycles = HasSpareGCCycles();
+    }
+
+    idleRequester = next;
+  }
+
+  if (!sIdleAndGCRequests.isEmpty() && HasSpareCycles(activeCount)) {
+    EnsureStarvationTimer();
+  }
+
+  if (sRecordGCTelemetry) {
+    sRecordGCTelemetry = false;
+    Telemetry::Accumulate(Telemetry::GC_WAIT_FOR_IDLE_COUNT, sNumWaitingGC);
+  }
+}
+
+void IdleSchedulerParent::EnsureStarvationTimer() {
+  // Even though idle runnables aren't really guaranteed to get run ever (which
+  // is why most of them have the timer fallback), try to not let any child
+  // process' idle handling to starve forever in case other processes are busy
+  if (!sStarvationPreventer) {
+    // Reuse StaticPrefs::page_load_deprioritization_period(), since that
+    // is used on child side when deciding the minimum idle period.
+    NS_NewTimerWithFuncCallback(
+        &sStarvationPreventer, StarvationCallback, nullptr,
+        StaticPrefs::page_load_deprioritization_period(),
+        nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY, "StarvationCallback");
+  }
+}
+
+void IdleSchedulerParent::StarvationCallback(nsITimer* aTimer, void* aData) {
+  RefPtr<IdleSchedulerParent> idleRequester = sIdleAndGCRequests.getFirst();
+  while (idleRequester) {
+    if (idleRequester->IsWaitingForIdle()) {
+      // Treat the first process waiting for idle time as running prioritized
+      // operation so that it gets run.
+      ++idleRequester->mRunningPrioritizedOperation;
+      ++sChildProcessesRunningPrioritizedOperation;
+      Schedule(idleRequester);
+      --idleRequester->mRunningPrioritizedOperation;
+      --sChildProcessesRunningPrioritizedOperation;
+      break;
+    }
+
+    idleRequester = idleRequester->getNext();
+  }
+  NS_RELEASE(sStarvationPreventer);
+}
+
+}  // namespace mozilla::ipc