llvm-project/compiler-rt/lib/xray/xray_profile_collector.h

//===-- xray_profile_collector.h -------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is a part of XRay, a dynamic runtime instrumentation system.
//
// This file defines the interface for a data collection service, for XRay
// profiling. What we implement here is an in-process service where
// FunctionCallTrie instances can be handed off by threads, to be
// consolidated/collected.
//
//===----------------------------------------------------------------------===//
#ifndef XRAY_XRAY_PROFILE_COLLECTOR_H
#define XRAY_XRAY_PROFILE_COLLECTOR_H

#include "xray_function_call_trie.h"

#include "xray/xray_log_interface.h"

namespace __xray {

/// The ProfileCollectorService implements a centralised mechanism for
/// collecting FunctionCallTrie instances, indexed by thread ID. On demand, the
/// ProfileCollectorService can be queried for the most recent state of the
/// data, in a form that allows traversal.
namespace profileCollectorService {

/// Posts the FunctionCallTrie associated with a specific Thread ID. This
/// will:
///
///   - Make a copy of the FunctionCallTrie and store that against the Thread
///     ID. This will use the global allocator for the service-managed
///     FunctionCallTrie instances.
///   - Queue up a pointer to the FunctionCallTrie.
///   - If the queue is long enough (longer than some arbitrary threshold) we
///     then pre-calculate a single FunctionCallTrie for the whole process.
///
///
/// We are making a copy of the FunctionCallTrie because the intent is to have
/// this function be called at thread exit, or soon after the profiling
/// handler is finalized through the XRay APIs. By letting threads each
/// process their own thread-local FunctionCallTrie instances, we're removing
/// the need for synchronisation across threads while we're profiling.
/// However, once we're done profiling, we can then collect copies of these
/// FunctionCallTrie instances and pay the cost of the copy.
///
/// NOTE: In the future, if this turns out to be more costly than "moving" the
/// FunctionCallTrie instances from the owning thread to the collector
/// service, then we can change the implementation to do it this way (moving)
/// instead.
void post(const FunctionCallTrie &T, tid_t TId);

/// The serialize will process all FunctionCallTrie instances in memory, and
/// turn those into specifically formatted blocks, each describing the
/// function call trie's contents in a compact form. In memory, this looks
/// like the following layout:
///
///   - block size (32 bits)
///   - block number (32 bits)
///   - thread id (64 bits)
///   - list of records:
///     - function ids in leaf to root order, terminated by
///       0 (32 bits per function id)
///     - call count (64 bit)
///     - cumulative local time (64 bit)
///     - record delimiter (64 bit, 0x0)
///
void serialize();

/// The reset function will clear out any internal memory held by the
/// service. The intent is to have the resetting be done in calls to the
/// initialization routine, or explicitly through the flush log API.
void reset();

/// This nextBuffer function is meant to implement the iterator functionality,
/// provided in the XRay API.
XRayBuffer nextBuffer(XRayBuffer B);

} // namespace profileCollectorService

} // namespace __xray

#endif // XRAY_XRAY_PROFILE_COLLECTOR_H