xref: /external/perfetto/include/perfetto/ext/tracing/core/shared_memory_arbiter.h

/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef INCLUDE_PERFETTO_EXT_TRACING_CORE_SHARED_MEMORY_ARBITER_H_
#define INCLUDE_PERFETTO_EXT_TRACING_CORE_SHARED_MEMORY_ARBITER_H_

#include <stddef.h>

#include <functional>
#include <memory>
#include <vector>

#include "perfetto/base/export.h"
#include "perfetto/ext/tracing/core/basic_types.h"
#include "perfetto/ext/tracing/core/shared_memory_abi.h"
#include "perfetto/ext/tracing/core/tracing_service.h"
#include "perfetto/tracing/buffer_exhausted_policy.h"

namespace perfetto {

namespace base {
class TaskRunner;
}

class SharedMemory;
class TraceWriter;

// Used by the Producer-side of the transport layer to vend TraceWriters
// from the SharedMemory it receives from the Service-side.
class PERFETTO_EXPORT_COMPONENT SharedMemoryArbiter {
 public:
  using ShmemMode = SharedMemoryABI::ShmemMode;

  virtual ~SharedMemoryArbiter();

  // Creates a new TraceWriter and assigns it a new WriterID. The WriterID is
  // written in each chunk header owned by a given TraceWriter and is used by
  // the Service to reconstruct TracePackets written by the same TraceWriter.
  // Returns null impl of TraceWriter if all WriterID slots are exhausted. The
  // writer will commit to the provided |target_buffer|. If the arbiter was
  // created via CreateUnbound() or CreateStartupTraceWriter() is later used,
  // only BufferExhaustedPolicy::kDrop is supported.
  virtual std::unique_ptr<TraceWriter> CreateTraceWriter(
      BufferID target_buffer,
      BufferExhaustedPolicy buffer_exhausted_policy =
          BufferExhaustedPolicy::kDefault) = 0;

  // Creates a TraceWriter that will commit to the target buffer with the given
  // reservation ID (creating a new reservation for this ID if none exists yet).
  // The buffer reservation should be bound to an actual BufferID via
  // BindStartupTargetBuffer() once the actual BufferID is known. Calling this
  // method may transition the arbiter into unbound state (see state diagram in
  // SharedMemoryArbiterImpl's class comment) and requires that all (past and
  // future) TraceWriters are created with BufferExhaustedPolicy::kDrop.
  //
  // While any unbound buffer reservation exists, all commits will be buffered
  // until all reservations were bound. Thus, until all reservations are bound,
  // the data written to the SMB will not be consumed by the service - the SMB
  // size should be chosen with this in mind. Startup writers always use
  // BufferExhaustedPolicy::kDrop, as we cannot feasibly stall while not
  // flushing to the service.
  //
  // The |target_buffer_reservation_id| should be greater than 0 but can
  // otherwise be freely chosen by the producer and is only used to translate
  // packets into the actual buffer id once
  // BindStartupTargetBuffer(reservation_id) is called. For example, Chrome uses
  // startup tracing not only for the first, but also subsequent tracing
  // sessions (to enable tracing in the browser process before it instructs the
  // tracing service to start tracing asynchronously, minimizing trace data loss
  // in the meantime), and increments the reservation ID between sessions.
  // Similarly, if more than a single target buffer per session is required
  // (e.g. for two different data sources), different reservation IDs should be
  // chosen for different target buffers.
  virtual std::unique_ptr<TraceWriter> CreateStartupTraceWriter(
      uint16_t target_buffer_reservation_id) = 0;

  // Should only be called on unbound SharedMemoryArbiters. Binds the arbiter to
  // the provided ProducerEndpoint and TaskRunner. Should be called only once
  // and on the provided |TaskRunner|. Usually called by the producer (i.e., no
  // specific data source) once it connects to the service. Both the endpoint
  // and task runner should remain valid for the remainder of the arbiter's
  // lifetime.
  virtual void BindToProducerEndpoint(TracingService::ProducerEndpoint*,
                                      base::TaskRunner*) = 0;

  // Binds commits from TraceWriters created via CreateStartupTraceWriter() with
  // the given |target_buffer_reservation_id| to |target_buffer_id|. May only be
  // called once per |target_buffer_reservation_id|. Should be called on the
  // arbiter's TaskRunner, and after BindToProducerEndpoint() was called.
  // Usually, it is called by a specific data source, after it received its
  // configuration (including the target buffer ID) from the service.
  virtual void BindStartupTargetBuffer(uint16_t target_buffer_reservation_id,
                                       BufferID target_buffer_id) = 0;

  // Treat the reservation as resolved to an invalid buffer. Commits for this
  // reservation will be flushed to the service ASAP. The service will free
  // committed chunks but otherwise ignore them. The producer can call this
  // method, for example, if connection to the tracing service failed or the
  // session was stopped concurrently before the connection was established.
  virtual void AbortStartupTracingForReservation(
      uint16_t target_buffer_reservation_id) = 0;

  // Notifies the service that all data for the given FlushRequestID has been
  // committed in the shared memory buffer. Should only be called while bound.
  virtual void NotifyFlushComplete(FlushRequestID) = 0;

  // Sets the duration during which commits are batched. Args:
  // |batch_commits_duration_ms|: The length of the period, during which commits
  // by all trace writers are accumulated, before being sent to the service.
  // When the period ends, all accumulated commits are flushed. On the first
  // commit after the last flush, another delayed flush is scheduled to run in
  // |batch_commits_duration_ms|. If an immediate flush occurs (via
  // FlushPendingCommitDataRequests()) during a batching period, any
  // accumulated commits up to that point will be sent to the service
  // immediately. And when the batching period ends, the commits that occurred
  // after the immediate flush will also be sent to the service.
  //
  // If the duration has already been set to a non-zero value before this method
  // is called, and there is already a scheduled flush with the previously-set
  // duration, the new duration will take effect after the scheduled flush
  // occurs.
  //
  // If |batch_commits_duration_ms| is non-zero, batched data that hasn't been
  // sent could be lost at the end of a tracing session. To avoid this,
  // producers should make sure that FlushPendingCommitDataRequests is called
  // after the last TraceWriter write and before the service has stopped
  // listening for commits from the tracing session's data sources (i.e.
  // data sources should stop asynchronously, see
  // DataSourceDescriptor.will_notify_on_stop=true).
  virtual void SetBatchCommitsDuration(uint32_t batch_commits_duration_ms) = 0;

  // Called to enable direct producer-side patching of chunks that have not yet
  // been committed to the service. The return value indicates whether direct
  // patching was successfully enabled. It will be true if
  // SharedMemoryArbiter::SetDirectSMBPatchingSupportedByService has been called
  // and false otherwise.
  virtual bool EnableDirectSMBPatching() = 0;

  // When the producer and service live in separate processes, this method
  // should be called if the producer receives an
  // InitializeConnectionResponse.direct_smb_patching_supported set to true by
  // the service (see producer_port.proto) .
  //
  // In the in-process case, the service will always support direct SMB patching
  // and this method should always be called.
  virtual void SetDirectSMBPatchingSupportedByService() = 0;

  // Forces an immediate commit of the completed packets, without waiting for
  // the next task or for a batching period to end. Should only be called while
  // bound.
  virtual void FlushPendingCommitDataRequests(
      std::function<void()> callback = {}) = 0;

  // Attempts to shut down this arbiter. This function prevents new trace
  // writers from being created for this this arbiter, but if there are any
  // existing trace writers, the shutdown cannot proceed and this funtion
  // returns false. The caller should not delete the arbiter before all of its
  // associated trace writers have been destroyed and this function returns
  // true.
  virtual bool TryShutdown() = 0;

  // Create a bound arbiter instance. Args:
  // |SharedMemory|: the shared memory buffer to use.
  // |page_size|: a multiple of 4KB that defines the granularity of tracing
  // pages. See tradeoff considerations in shared_memory_abi.h.
  // |ProducerEndpoint|: The service's producer endpoint used e.g. to commit
  // chunks and register trace writers.
  // |TaskRunner|: Task runner for perfetto's main thread, which executes the
  // OnPagesCompleteCallback and IPC calls to the |ProducerEndpoint|.
  //
  // Implemented in src/core/shared_memory_arbiter_impl.cc.
  static std::unique_ptr<SharedMemoryArbiter> CreateInstance(
      SharedMemory*,
      size_t page_size,
      ShmemMode,
      TracingService::ProducerEndpoint*,
      base::TaskRunner*);

  // Create an unbound arbiter instance, which should later be bound to a
  // ProducerEndpoint and TaskRunner by calling BindToProducerEndpoint(). The
  // returned arbiter will ONLY support trace writers with
  // BufferExhaustedPolicy::kDrop.
  //
  // An unbound SharedMemoryArbiter can be used to write to a producer-created
  // SharedMemory buffer before the producer connects to the tracing service.
  // The producer can then pass this SMB to the service when it connects (see
  // TracingService::ConnectProducer).
  //
  // To trace into the SMB before the service starts the tracing session, trace
  // writers can be obtained via CreateStartupTraceWriter() and later associated
  // with a target buffer via BindStartupTargetBuffer(), once the target buffer
  // is known.
  //
  // Implemented in src/core/shared_memory_arbiter_impl.cc. See CreateInstance()
  // for comments about the arguments.
  static std::unique_ptr<SharedMemoryArbiter>
  CreateUnboundInstance(SharedMemory*, size_t page_size, ShmemMode mode);
};

}  // namespace perfetto

#endif  // INCLUDE_PERFETTO_EXT_TRACING_CORE_SHARED_MEMORY_ARBITER_H_