When Dallas returned Wednesday night on TNT, one of television’s most extended breaks came to an end.

Even by “Mad Men’s” standards, 21 years is an unusually long hiatus, but as reviewer Troy Patterson has noted, “Dallas” has been with us the whole time in other ways: Some of the devices it pioneered have become television’s most annoying institutions.

Everyone who has screamed in aggravation when, after 22 episodes, a TV season leaves crucial details unresolved, can thank the original “Dallas” for the cliffhanger season finale.

The show’s third season ended with J.R. lying in a pool of blood and the world’s media wondering whodunit. It really was a global phenomenon. Three hundred million people tuned in nine months later to learn the answer to what they knew would one day become a classic trivia question.

Six seasons later, “Dallas” perpetrated another crime against narrative when Bobby Ewing, J.R.’s angelic brother, showed-up in the shower a year after he’d been the guest of honor at a weepy Southfork funeral.

He later explained to his astonished wife, Pam, that the events of the previous season – including her remarriage – had all been a terrible dream. Fortunately, the dream gambit has made few reappearances in quality television. It is a high-degree-of-difficulty move reserved for truly deft, demented, or dopey creative teams.

But the “Who Shot J.R.” imbroglio left another legacy. Do you remember the season finale of this year’s “The Good Wife” when Kalinda Sharma sat in an armchair facing a locked door, waiting for a mysterious character to appear?

Or what about the final scene of “Suburgatory,” when Tessa was shocked to meet … well, we didn’t see whom she met.

Why weren’t these key characters shown?

In the 1980 off-season, when what seemed like the entire world was wondering who had attacked J.R., Larry Hagman staged a one-man strike.

According to the oral history of “Dallas” that appears in a recent Entertainment Weekly, Hagman’s demands were outrageous by the standards of the day, but as Kim LeMasters of CBS told EW, “We were caught and he knew it. What are you going to do, replace Larry Hagman?”

Hagman got his raise. (He also held out for better terms for the TNT reboot, according to TV Guide.)

Dick Wolf pioneered the actor-as-interchangeable-cog model while developing “Law & Order” to avoid giving them the kind of leverage that Hagman had used so effectively.

And these days, showrunners go to great lengths to avoid showing actors who aren’t yet on contract in season finales.

Thanks to J.R. Ewing, cliffhangers can be a pricey bit of casting.