CefSharedProcessMessageBuilder

Header: cef_shared_process_message_builder.h
Category: V8 & Process Messaging

Overview

JavaScript bridge, value tree, inter-process messages, shared memory regions.

CefSharedProcessMessageBuilder

Source File: include/cef_shared_process_message_builder.h

Process / Thread Context: Not specified in header. The class is documented as "not thread-safe but may be used exclusively on a different thread from the one which constructed it" — i.e. once built on one thread, it may be used (Memory/Size/Build) on another thread provided the embedder serializes access.

Purpose: Class that builds a CefProcessMessage containing a shared memory region. Use it when you need to send a large payload (e.g. a frame buffer) between processes without copying the bytes through IPC marshalling.

Methods

`static CefRefPtr<CefSharedProcessMessageBuilder> Create(const CefString& name, size_t byte_size)`

Parameters:

name: The message name (same as CefProcessMessage::Create(name)).
byte_size: The size in bytes of the shared memory region to allocate.

Return Value: Returns a new builder instance. Check IsValid() before using.

Usage Instruction: Create the builder, fill the writable memory via Memory(), then call Build() to obtain the final CefProcessMessage.

Threading Constraint: Not specified; the resulting builder is not thread-safe.

`virtual bool IsValid()`

Parameters:

None.

Return Value: Returns true if the builder is valid.

Usage Instruction: Always check before Memory(), Size(), or Build().

Threading Constraint: Not specified in header (class is not thread-safe).

`virtual size_t Size()`

Parameters:

None.

Return Value: Returns the size of the shared memory region in bytes. Returns 0 for invalid instances.

Usage Instruction: Use to know how many bytes you can write to Memory().

Threading Constraint: Not specified in header.

`virtual void* Memory()`

Parameters:

None.

Return Value: Returns the pointer to the writable memory. Returns nullptr for invalid instances. The returned pointer is only valid for the life span of this object.

Usage Instruction: Write your payload into this buffer before calling Build(). Do not retain the pointer past the builder's lifetime.

Threading Constraint: Not specified in header.

`virtual CefRefPtr<CefProcessMessage> Build()`

Parameters:

None.

Return Value: Returns the assembled CefProcessMessage. Returns nullptr for invalid instances. Invalidates the builder instance — the returned message takes ownership of the shared memory region.

Usage Instruction: Call once after writing the payload. After Build() returns, do not call any further methods on this builder; send the returned CefProcessMessage via CefBrowser::SendProcessMessage (or CefFrame::SendProcessMessage).

Threading Constraint: Not specified in header.

Usage Example

cpp

// === Send a large blob from the render process to the browser ===
void SendSharedBlob(CefRefPtr<CefBrowser> browser,
                    const std::vector<uint8_t>& bytes) {
  CefRefPtr<CefSharedProcessMessageBuilder> builder =
      CefSharedProcessMessageBuilder::Create("shared-blob", bytes.size());
  if (!builder || !builder->IsValid()) return;

  memcpy(builder->Memory(), bytes.data(), bytes.size());

  CefRefPtr<CefProcessMessage> msg = builder->Build();
  if (msg && msg->IsValid())
    browser->SendProcessMessage(PID_BROWSER, msg);
}

// On the browser side, use CefProcessMessage::GetSharedMemoryRegion() to
// access the bytes (see CefSharedMemoryRegion usage example above).

CefSharedProcessMessageBuilder ​

Overview ​