context.h

/*
 * Copyright 2021, 2022 Datadog, Inc
 *
 * 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 _CONTEXT_H
#define _CONTEXT_H

#include "arch.h"
#include "arguments.h"
#include "os.h"

static const u32 DD_TAGS_CAPACITY = 10;

typedef struct {
    u32 value;
} Tag;

class Context {
  public:
    u64 spanId;
    u64 rootSpanId;
    u64 checksum;
    Tag tags[DD_TAGS_CAPACITY];

    Tag get_tag(int i) {
        return tags[i];
    }
};

// must be kept in sync with PAGE_SIZE in JavaProfiler.java
const int DD_CONTEXT_PAGE_SIZE = 1024;
const int DD_CONTEXT_PAGE_MASK = DD_CONTEXT_PAGE_SIZE - 1;
const int DD_CONTEXT_PAGE_SHIFT = __builtin_popcount(DD_CONTEXT_PAGE_MASK);

typedef struct {
    const int capacity;
    const Context* storage;
} ContextPage;

class Contexts {

  private:
    static int _max_pages;
    static Context** _pages;
    static void initialize(int pageIndex);

  public:
    // get must not allocate
    static Context& get(int tid);
    static Context& empty();
    // not to be called except to share with Java callers as a DirectByteBuffer
    static ContextPage getPage(int tid);
    static int getMaxPages(int maxTid = OS::getMaxThreadId());

    // this *MUST* be called only when the profiler is completely stopped
    static void reset();
};

#endif /* _CONTEXT_H */