The writer of “Training Day” and “Harsh Times” brings us more cop movie grit with “End of Watch,” a vivid series of impressionistic sketches of a year in the lives of two Los Angeles police officers.

They’re just patrolmen, in a family of officers — sometimes heroic, often cocky, occasionally miscalculating. In telling their stories episodically, with a rhythm that builds suspense slowly, Ayer gets at the level of trust they have to have for one another and the meaning of that old cop movie cliche — “He took a bullet for me.”

Brian Taylor (Jake Gyllenhaal) and Mike Zavala (Michael Pena) may be young, but they’ve been partners so long they’re like an old married couple — comically bickering, teasing, picking at each other’s sore spots. Brian is the single one, the ambitious one. He wants to make detective. He’s willing to take a shortcut or two to get there.

Mike is more blue collar — happily married, a father, happy to be where he is in the force. But the uniform hasn’t taken the chip off his shoulder. Call him the wrong name when he’s arresting you and it’s “Go time.”

Pena and Gyllenhaal so fully inhabit these well-rounded characters that you worry what will become of them.