Fix race condition in ShaderCompilerService (#7147)

filament/backend/src/opengl/ShaderCompilerService.cpp

@@ -103,6 +103,11 @@ struct ShaderCompilerService::OpenGLProgramToken : ProgramToken {
         return programData;
     }
 
+    void wait() const noexcept {
+        std::unique_lock l(lock);
+        cond.wait(l, [this](){ return signaled; });
+    }
+
     // Checks if the programBinary is ready.
     // This is similar to std::future::wait_for(0s)
     bool isReady() const noexcept {
@@ -338,6 +343,22 @@ GLuint ShaderCompilerService::getProgram(ShaderCompilerService::program_token_t&
 
     token->compiler.cancelTickOp(token);
 
+    if (token->compiler.mShaderCompilerThreadCount) {
+        auto job = token->compiler.mCompilerThreadPool.dequeue(token);
+        if (!job) {
+            // The job is being executed right now. We need to wait for it to finish to avoid a
+            // race.
+            token->wait();
+        } else {
+            // The job has not been executed, but we still need to inform the callback manager in
+            // order for future callbacks to be successfully called.
+            token->compiler.mCallbackManager.put(token->handle);
+        }
+    } else {
+        // Since the tick op was canceled, we need to .put the token here.
+        token->compiler.mCallbackManager.put(token->handle);
+    }
+
     for (GLuint& shader: token->gl.shaders) {
         if (shader) {
             if (token->gl.program) {