503571 - Let user code refer to fragments by weak pointers

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, enhancement)

Description

[David Mandelin [:dmandelin]]

Currently, code that uses Nanojit uses hash keys to refer to fragments and hash lookups to access fragments. Clearly, a pointer would be a simpler, faster way to check for and access fragments and/or fragment code. But a plain pointer will not work because the Nanojit might clear out the referent fragment at any time.

Weak pointers would work. Example API:

  template<typename T>
  class WeakPtr { 
  public:
    T* get() const;    // return ptr value or NULL.
  }

  // In jstracer.cpp
  WeakPtr<Fragment> getAnchor(...) { ... }

  // In Nanojit
  WeakPtr<uint8>    compile(...) { ... }

As an example of usage, JSRegExp could get a WeakPtr<uint8> for the compiled code. If the pointer has a value, we simply call it. If not, we compile the new code. No hash lookups, no hash functions, no need to copy the regexp to a Nanojit-owned buffer.

Comment 1

[Edwin Smith]

Tamarin has weak pointers but fragments are short lived (See MMgc/GCWeakRef.h).  Changing product to Tracemonkey.

Comment 2

[Ryan VanderMeulen [:RyanVM]]

Obsolete with the removal of tracejit.