Vector Guide

Overview

HSHM provides two vector variants: hshm::ipc::vector for shared memory and hshm::priv::vector for private memory. For standard ChiMod development, use std::vector. The HSHM vectors are needed when data must be accessible from GPU kernels or live in shared memory across processes.

hshm::ipc::vector

Source: hermes_shm/data_structures/ipc/vector.h

A dynamic array stored in shared memory using offset-based pointers (OffsetPtr<T>) for process-independent addressing.

#include <hermes_shm/data_structures/ipc/vector.h>

// Create with an allocator
hshm::ipc::vector<int, AllocT> vec(alloc, 10);  // 10 elements

// Standard vector operations
vec.push_back(42);
vec.emplace_back(100);
int val = vec[0];
vec.resize(20);
vec.reserve(50);
vec.clear();

// Iteration
for (auto it = vec.begin(); it != vec.end(); ++it) {
  process(*it);
}

Template Parameters:

• T - Element type
• AllocT - Allocator type (determines shared vs private memory)

Key Differences from std::vector:

• Requires an allocator at construction time
• Uses OffsetPtr<T> internally instead of raw pointers
• Safe for cross-process access in shared memory
• Annotated with HSHM_CROSS_FUN for GPU compatibility

hshm::priv::vector

Source: hermes_shm/data_structures/priv/vector.h

A private-memory vector with allocator integration. Supports the same API as std::vector plus serialization.

#include <hermes_shm/data_structures/priv/vector.h>

// Standard construction
hshm::priv::vector<int> vec = {1, 2, 3, 4, 5};
hshm::priv::vector<int> vec2(10, 0);  // 10 zeros

// Full STL-compatible API
vec.push_back(6);
vec.pop_back();
vec.insert(vec.begin() + 2, 99);
vec.erase(vec.begin());

// Reverse iteration
for (auto it = vec.rbegin(); it != vec.rend(); ++it) {
  process(*it);
}

Optimizations:

• Uses memcpy/memmove for trivially copyable types (POD optimization)
• Exponential capacity growth strategy
• Annotated with HSHM_CROSS_FUN for GPU compatibility

When to Use Each

Variant	Use Case
std::vector	Default choice for ChiMod task data
hshm::priv::vector	Private memory with serialization support or GPU access
hshm::ipc::vector	Cross-process shared memory regions

Related Documentation

• Allocator Guide - Memory allocators used by these vectors