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Diffstat (limited to 'docs/MESA_multithread_makecurrent.spec')
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1 files changed, 158 insertions, 0 deletions
diff --git a/docs/MESA_multithread_makecurrent.spec b/docs/MESA_multithread_makecurrent.spec new file mode 100644 index 00000000000..5065c2fc0a3 --- /dev/null +++ b/docs/MESA_multithread_makecurrent.spec @@ -0,0 +1,158 @@ +Name + + MESA_multithread_makecurrent + +Name Strings + + GLX_MESA_multithread_makecurrent + +Contact + + Eric Anholt ([email protected]) + +Status + + Not shipping. + +Version + + Last Modified Date: 21 February 2011 + +Number + + TBD + +Dependencies + + OpenGL 1.0 or later is required. + GLX 1.3 or later is required. + +Overview + + The GLX context setup encourages multithreaded applications to + create a context per thread which each operate on their own + objects in parallel, and leaves synchronization for write access + to shared objects up to the application. + + For some applications, maintaining per-thread contexts and + ensuring that the glFlush happens in one thread before another + thread starts working on that object is difficult. For them, + using the same context across multiple threads and protecting its + usage with a mutex is both higher performance and easier to + implement. This extension gives those applications that option by + relaxing the context binding requirements. + + This new behavior matches the requirements of AGL, while providing + a feature not specified in WGL. + +IP Status + + Open-source; freely implementable. + +Issues + + None. + +New Procedures and Functions + + None. + +New Tokens + + None. + +Changes to Chapter 2 of the GLX 1.3 Specification (Functions and Errors) + + Replace the following sentence from section 2.2 Rendering Contexts: + In addition, a rendering context can be current for only one + thread at a time. + with: + In addition, an indirect rendering context can be current for + only one thread at a time. A direct rendering context may be + current to multiple threads, with synchronization of access to + the context thruogh the GL managed by the application through + mutexes. + +Changes to Chapter 3 of the GLX 1.3 Specification (Functions and Errors) + + Replace the following sentence from section 3.3.7 Rendering Contexts: + If ctx is current to some other thread, then + glXMakeContextCurrent will generate a BadAccess error. + with: + If ctx is an indirect context current to some other thread, + then glXMakeContextCurrent will generate a BadAccess error. + + Replace the following sentence from section 3.5 Rendering Contexts: + If ctx is current to some other thread, then + glXMakeCurrent will generate a BadAccess error. + with: + If ctx is an indirect context current to some other thread, + then glXMakeCurrent will generate a BadAccess error. + +GLX Protocol + + None. The GLX extension only extends to direct rendering contexts. + +Errors + + None. + +New State + + None. + +Issues + + (1) What happens if the app binds a context/drawable in multiple + threads, then binds a different context/thread in one of them? + + As with binding a new context from the current thread, the old + context's refcount is reduced and the new context's refcount is + increased. + + (2) What happens if the app binds a context/drawable in multiple + threads, then binds None/None in one of them? + + The GLX context is unreferenced from that thread, and the other + threads retain their GLX context binding. + + (3) What happens if the app binds a context/drawable in 7 threads, + then destroys the context in one of them? + + As with GLX context destruction previously, the XID is destroyed + but the context remains usable by threads that have the context + current. + + (4) What happens if the app binds a new drawable/readable with + glXMakeCurrent() when it is already bound to another thread? + + The context becomes bound to the new drawable/readable, and + further rendering in either thread will use the new + drawable/readable. + + (5) What requirements should be placed on the user managing contexts + from multiple threads? + + The intention is to allow multithreaded access to the GL at the + minimal performance cost, so requiring that the GL do general + synchronization (beyond that already required by context sharing) + is not an option, and synchronizing of GL's access to the GL + context between multiple threads is left to the application to do + across GL calls. However, it would be unfortunate for a library + doing multithread_makecurrent to require that other libraries + share in synchronization for binding of their own contexts, so the + refcounting of the contexts is required to be threadsafe. + + (6) Does this apply to indirect contexts? + + This was ignored in the initial revision of the spec. Behavior + for indirect contexts is left as-is. + +Revision History + + 20 November 2009 Eric Anholt - initial specification + 22 November 2009 Eric Anholt - added issues from Ian Romanick. + 3 February 2011 Eric Anholt - updated with resolution to issues 1-3 + 3 February 2011 Eric Anholt - added issue 4, 5 + 21 February 2011 Eric Anholt - Include glXMakeCurrent() sentence + along with glXMakeContextCurrent() for removal. |