Hi I am trying to modify the GHC rts so that every time a transaction fails to commit, instead of automatically restart it, I want to preempted and add it to the end of the task queue of its HEC. The problem is, when I try to call yield at the point of the ATOMICALLY_FRAME code where the transaction is restarted, I get this error message:

...

Main: Control.Concurrent.STM.atomically was nested Main: thread blocked indefinitely in an MVar operation

The point in the code of PrimOps.cmm I try to put my code is as below. PrimOps.cmm 1074 /* Transaction was not valid: try again */ 1075 ("ptr" trec) = ccall stmStartTransaction(MyCapability() "ptr", 1076 NO_TREC "ptr"); 1077 StgTSO_trec(CurrentTSO) = trec; 1078 1079 /* call yield function here */ Capability_context_switch(MyCapability()) = 1 :: CInt; jump stg_yield_noregs(); /* */ 1080 jump stg_ap_v_fast 1081 // push the StgAtomicallyFrame again: the code generator is 1082 // clever enough to only assign the fields that have changed. 1083 (ATOMICALLY_FRAME_FIELDS(,,info_ptr,p1,p2, 1084 code,frame_result)) 1085 (code); My doubts are: Is it possible to make a preemption at that point in the ATOMICALLY_FRAME code?. If it is possible, how do I proceed? Thanks for the attention. Best regards. -- *Rodrigo M. Duarte* Bacharelado em Engenharia de Computação LUPS - Laboratory of Ubiquitous and Parallel Systems Computação de Alto Desempenho Sustentável Universidade Federal de Pelotas - UFPel [image: image_png_part?hl=pt&part=2&thumb=1] *Antes de imprimir este e-mail pense em sua responsabilidade e compromisso com o Meio Ambiente. **Só imprima se for realmente necessário. * *Before printing this e-mail consider its responsibility and commitment to the environment. Only print if it is really necessary. *