# GLFW Shared Contexts
**URL:** https://discourse.glfw.org/t/glfw-shared-contexts/1707
**Category:** support
**Created:** [November 26, 2020, 12:03am UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707 "2020-11-26T00:03:05Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@stephane](https://discourse.glfw.org/u/stephane)
#### Post date: [November 26, 2020, 12:03am UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/1 "2020-11-26T00:03:05Z")
Hi,
I am currently working on my game framework (c++, GLFW 3.3.2, OpenGL 4.4).
I would like to add to possibility to work with multiple windows. In that purpose, i start working with shared contexts.
So i created a ‘useless’ window that is hidden and that just deserves to share its context with any new ‘real’ windows (call this window FAKE1)
In my tests i created 2 other game windows as a proof of concept, sharing FAKE1 context (call them GAME1 and GAME2)
At first, this works fine, but as soon as i close one of the 2 games window the display collapses.
-I checked that before rendering GAME1 or GAME2 i set the concerned window’s context current
-I checked that before creating GAME1 or GAME2, the FAKE1 context is not current (as mentionned in glfwCreateWindow documentation)
-In my code, Textures et VertexBuffer are shared but not VertexArray (while such objects seem not to be sharable)
-The code is not multithreaded
The application i made is constantly allocating new resources. Is this an issue ?
Does the active context when a texture/buffer is beeing created of any concern ?
Must i always allocate resources with FAKE1 context ?
Can i create resources with GAME1 context active and use it inside GAME2 ? destroy it inside GAME2 ?
I am using glew to retreive OpenGL functions pointers. Can theses pointers be different between contexts ?
Thank you for your help.
---
### Author:  [@dougbinks](https://discourse.glfw.org/u/dougbinks)
#### Post date: [November 26, 2020, 12:52pm UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/2 "2020-11-26T12:52:50Z")
> [@stephane](#):
>
> At first, this works fine, but as soon as i close one of the 2 games window the display collapses.
GLFW itself does not close windows, it is your own code which calls `glfwDestroyWindow`. Are you accidentally closing all windows when `glfwWindowShouldClose` returns true for one?
In general a problem like this should be solved by debugging the code (with a debugger such as Visual Studio or GDB), or adding `printf` statements to check the code flow is as expected.
> [@stephane](#):
>
> The application i made is constantly allocating new resources. Is this an issue ?
This is not an issue in general.
> [@stephane](#):
>
> Does the active context when a texture/buffer is beeing created of any concern ?
Not usually.
> [@stephane](#):
>
> Must i always allocate resources with FAKE1 context ?
No, you can allocate shareable resources on any of the shared contexts.
> [@stephane](#):
>
> Can i create resources with GAME1 context active and use it inside GAME2 ? destroy it inside GAME2 ?
Yes, so long as the resource is not bound in GAME1 when destroyed in GAME2, though this usually just results in incorrect rendering rather than a crash due to most OpenGL drivers being fairly fault tolerant.
> [@stephane](#):
>
> I am using glew to retreive OpenGL functions pointers. Can theses pointers be different between contexts ?
No, they should be the same.
---
### Author:  [@stephane](https://discourse.glfw.org/u/stephane)
#### Post date: [November 26, 2020, 1:13pm UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/3 "2020-11-26T13:13:03Z")
Thank you for your answers.
Concerning the GAME window closure, i destroy a single window at a time with glfwDestroyWindow. The other remains alive but it becomes black or its rendering is corrupted.
What thing i do not always make is unbind the resources after rendering in one context.
for pseudo code example
```
// rendering
glfwMakeCurrentContext(my_game1);
glUseProgram(program_id);
glBindVertexArray(vertex_array_id);
glBindVertexArray(0);
// do not : glUseProgram(0);
glfwMakeCurrentContext(nullptr);
// destroying the window
// at this point the program (and its attributes) are still bound to the context being destroyed,
// and i expect to be able to still use program_id in my_game2
glfwDestroyWindow(my_game1);
```
So you are telling me that i should ensure that glUseProgram(0) is being called before destruction (and so on for other resources) ?
Thank you
---
### Author:  [@stephane](https://discourse.glfw.org/u/stephane)
#### Post date: [November 29, 2020, 3:55pm UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/4 "2020-11-29T15:55:05Z")
Thank for your help.
It seems i found what caused my issue. I want to share that knowledge.
Vertex Array Objects (VAO) are not shared among shared context (I knew that) but i did not realized at first that two VAOs with same ID could exist at the same time (as soon as they belong to different contexts)
In my code there was 2 VAO with the same id. After having destroyed my window Game1, i was destroying such a VAO but with the Game2 context current. This was destroying the wrong resource for the wrong context.
I hope this will help
---
### Author:  [@dougbinks](https://discourse.glfw.org/u/dougbinks)
#### Post date: [November 29, 2020, 4:44pm UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/5 "2020-11-29T16:44:54Z")
Glad you found the issue, and thanks for posting the answer - that should help folk with similar problems!
---
### Author:  [@dougbinks](https://discourse.glfw.org/u/dougbinks)
#### Post date: [September 6, 2026, 6:08pm UTC](https://discourse.glfw.org/t/glfw-shared-contexts/1707/6 "2026-09-06T18:08:05Z")
A post was split to a new topic: [Can you please explain what context sharing then means?](https://discourse.glfw.org/t/can-you-please-explain-what-context-sharing-then-means/3023)