StgBool stmCommitTransaction()

in rts/STM.c [1046:1116]
48 lines of code
10 McCabe index (conditional complexity)

StgBool stmCommitTransaction(Capability *cap, StgTRecHeader *trec) {
  StgInt64 max_commits_at_start = max_commits;

  TRACE("%p : stmCommitTransaction()", trec);
  ASSERT(trec != NO_TREC);

  lock_stm(trec);

  ASSERT(trec -> enclosing_trec == NO_TREC);
  ASSERT((trec -> state == TREC_ACTIVE) ||
         (trec -> state == TREC_CONDEMNED));

  // Use a read-phase (i.e. don't lock TVars we've read but not updated) if
  // the configuration lets us use a read phase.

  bool result = validate_and_acquire_ownership(cap, trec, (!config_use_read_phase), true);
  if (result) {
    // We now know that all the updated locations hold their expected values.
    ASSERT(trec -> state == TREC_ACTIVE);

    if (config_use_read_phase) {
      StgInt64 max_commits_at_end;
      StgInt64 max_concurrent_commits;
      TRACE("%p : doing read check", trec);
      result = check_read_only(trec);
      TRACE("%p : read-check %s", trec, result ? "succeeded" : "failed");

      max_commits_at_end = max_commits;
      max_concurrent_commits = ((max_commits_at_end - max_commits_at_start) +
                                (n_capabilities * TOKEN_BATCH_SIZE));
      if (((max_concurrent_commits >> 32) > 0) || shake()) {
        result = false;
      }
    }

    if (result) {
      // We now know that all of the read-only locations held their expected values
      // at the end of the call to validate_and_acquire_ownership.  This forms the
      // linearization point of the commit.

      // Make the updates required by the transaction.
      FOR_EACH_ENTRY(trec, e, {
        StgTVar *s;
        s = e -> tvar;
        if ((!config_use_read_phase) || (e -> new_value != e -> expected_value)) {
          // Either the entry is an update or we're not using a read phase:
          // write the value back to the TVar, unlocking it if necessary.

          ACQ_ASSERT(tvar_is_locked(s, trec));
          TRACE("%p : writing %p to %p, waking waiters", trec, e -> new_value, s);
          unpark_waiters_on(cap,s);
          IF_STM_FG_LOCKS({
            s -> num_updates ++;
          });
          unlock_tvar(cap, trec, s, e -> new_value, true);
        }
        ACQ_ASSERT(!tvar_is_locked(s, trec));
      });
    } else {
        revert_ownership(cap, trec, false);
    }
  }

  unlock_stm(trec);

  free_stg_trec_header(cap, trec);

  TRACE("%p : stmCommitTransaction()=%d", trec, result);

  return result;
}