If you’re expecting Joan Rivers: A Piece of Work to showcase her famously blue stand-up routines – a testament, perhaps, to the undiminished ferocity she still brings to the stage at 77 – you’ve got another think coming.

That’s not to say Ricki Stern and Anne Sundberg’s illuminating documentary, which closed the San Francisco Film Festival in May, isn’t funny. But the story it tells, of a comedy workaholic struggling to stay at the top of her profession, is also undeniably bittersweet.

“It’s not about whether the talent is good,” says agent Larry Thompson. “It’s about whether they’re hot.” Rivers isn’t cold, exactly – she works steadily, constantly writing plays, jokes and even a 2009 murder mystery inspired by her experience as a red-carpet Oscars host. She sells jewelry on cable TV. And she still finds time for more than 200 stand-up gigs per year.

But for a woman whose need to be busy seems almost pathological, and who still takes every perceived slight as a personal rejection, steady doesn’t cut it. Rivers craves success, as all performers do, but she has achieved that beyond any reasonable measure. She also demands the respect befitting a female stand-up who’s spent nearly half a century at or near the top of a male-dominated business.

When she stages her own play in London – A Work in Progress, a typically brutal bit of introspection – the audience gives her a standing ovation. Yet the press isn’t so kind, and she doesn't take the show to Broadway, largely because Rivers refuses to give her critics ammunition. Even at her own Comedy Central Roast, the barbs sting, and Rivers is seen fuming in her dressing room.

It’s a startling revelation, seeing the famously tough Rivers revealing such vulnerability, and one might understandably wonder why she would choose to be mocked, by comedians she considers beneath her, on national television. Well, that one’s easy: exposure. Rivers is a savvy self-promoter, and in her tireless quest to stay in the public consciousness, she makes concessions.

Stern and Sundberg delve into Rivers’ personal life, too – specifically, the devastation wrought by late husband Edgar’s suicide, and her impossibly close relationship with daughter Melissa, of whom she is fiercely protective. Yet all that is revealed in Piece of Work, personal and professional, portrays a woman clinging to the fame she considers rightfully hers, tormented by insecurities, desperate to stay “hot.”

“Good luck to the next queen of comedy, because she’s not abdicating,” says her manager Billy Sammeth, who thinks bookers see Rivers as a past-her-prime “plastic-surgery freak.” “There will be nail marks on that red carpet before she abdicates.” We believe it.

Joan Rivers: A Piece of Work opens Friday, June 11, at the Embarcadero Center Cinema. For tickets, click here.