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/*-------------------------------------------------------------------------
 *
 * latch.h
 *	  Routines for interprocess latches
 *
 * A latch is a boolean variable, with operations that let processes sleep
 * until it is set. A latch can be set from another process, or a signal
 * handler within the same process.
 *
 * The latch interface is a reliable replacement for the common pattern of
 * using pg_usleep() or select() to wait until a signal arrives, where the
 * signal handler sets a flag variable. Because on some platforms an
 * incoming signal doesn't interrupt sleep, and even on platforms where it
 * does there is a race condition if the signal arrives just before
 * entering the sleep, the common pattern must periodically wake up and
 * poll the flag variable. The pselect() system call was invented to solve
 * this problem, but it is not portable enough. Latches are designed to
 * overcome these limitations, allowing you to sleep without polling and
 * ensuring quick response to signals from other processes.
 *
 * There are two kinds of latches: local and shared. A local latch is
 * initialized by InitLatch, and can only be set from the same process.
 * A local latch can be used to wait for a signal to arrive, by calling
 * SetLatch in the signal handler. A shared latch resides in shared memory,
 * and must be initialized at postmaster startup by InitSharedLatch. Before
 * a shared latch can be waited on, it must be associated with a process
 * with OwnLatch. Only the process owning the latch can wait on it, but any
 * process can set it.
 *
 * There are three basic operations on a latch:
 *
 * SetLatch		- Sets the latch
 * ResetLatch	- Clears the latch, allowing it to be set again
 * WaitLatch	- Waits for the latch to become set
 *
 * WaitLatch includes a provision for timeouts (which should be avoided
 * when possible, as they incur extra overhead) and a provision for
 * postmaster child processes to wake up immediately on postmaster death.
 * See unix_latch.c for detailed specifications for the exported functions.
 *
 * The correct pattern to wait for event(s) is:
 *
 * for (;;)
 * {
 *	   ResetLatch();
 *	   if (work to do)
 *		   Do Stuff();
 *	   WaitLatch();
 * }
 *
 * It's important to reset the latch *before* checking if there's work to
 * do. Otherwise, if someone sets the latch between the check and the
 * ResetLatch call, you will miss it and Wait will incorrectly block.
 *
 * To wake up the waiter, you must first set a global flag or something
 * else that the wait loop tests in the "if (work to do)" part, and call
 * SetLatch *after* that. SetLatch is designed to return quickly if the
 * latch is already set.
 *
 * Presently, when using a shared latch for interprocess signalling, the
 * flag variable(s) set by senders and inspected by the wait loop must
 * be protected by spinlocks or LWLocks, else it is possible to miss events
 * on machines with weak memory ordering (such as PPC).  This restriction
 * will be lifted in future by inserting suitable memory barriers into
 * SetLatch and ResetLatch.
 *
 * On some platforms, signals will not interrupt the latch wait primitive
 * by themselves.  Therefore, it is critical that any signal handler that
 * is meant to terminate a WaitLatch wait calls SetLatch.
 *
 * Note that use of the process latch (PGPROC.procLatch) is generally better
 * than an ad-hoc shared latch for signaling auxiliary processes.  This is
 * because generic signal handlers will call SetLatch on the process latch
 * only, so using any latch other than the process latch effectively precludes
 * use of any generic handler.
 *
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/latch.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef LATCH_H
#define LATCH_H

#include <signal.h>

/*
 * Latch structure should be treated as opaque and only accessed through
 * the public functions. It is defined here to allow embedding Latches as
 * part of bigger structs.
 */
typedef struct
{
	sig_atomic_t is_set;
	bool		is_shared;
	int			owner_pid;
#ifdef WIN32
	HANDLE		event;
#endif
} Latch;

/* Bitmasks for events that may wake-up WaitLatch() clients */
#define WL_LATCH_SET		 (1 << 0)
#define WL_SOCKET_READABLE	 (1 << 1)
#define WL_SOCKET_WRITEABLE  (1 << 2)
#define WL_TIMEOUT			 (1 << 3)
#define WL_POSTMASTER_DEATH  (1 << 4)

/*
 * prototypes for functions in latch.c
 */
extern void InitializeLatchSupport(void);
extern void InitLatch(volatile Latch *latch);
extern void InitSharedLatch(volatile Latch *latch);
extern void OwnLatch(volatile Latch *latch);
extern void DisownLatch(volatile Latch *latch);
extern int	WaitLatch(volatile Latch *latch, int wakeEvents, long timeout);
extern int WaitLatchOrSocket(volatile Latch *latch, int wakeEvents,
				  pgsocket sock, long timeout);
extern void SetLatch(volatile Latch *latch);
extern void ResetLatch(volatile Latch *latch);

/* beware of memory ordering issues if you use this macro! */
#define TestLatch(latch) (((volatile Latch *) (latch))->is_set)

/*
 * Unix implementation uses SIGUSR1 for inter-process signaling.
 * Win32 doesn't need this.
 */
#ifndef WIN32
extern void latch_sigusr1_handler(void);
#else
#define latch_sigusr1_handler()  ((void) 0)
#endif

#endif   /* LATCH_H */

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ITAY HOD

Itay Hod, MMJ with KPIX/CBS in San Francisco, took the 5-Day Intensive Video Storytelling Bootcamp in 2018.

Because he works alone, with only an iPhone, he was able to embed himself with a homeless family.

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Kiet Do, an MMJ with KPIX/CBS in San Francisco, took the 5-Day Intensive Video Storytelling Bootcamp in 2021.

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Taylor Schaub, an MMJ with Spectrum News 1 in LA, took the 5-Day Intensive Video Storytelling Bootcamp in 2023.

Here is a story he turned in only one day, using only an iPhone. It was the first video story he ever did and it was nominated for an Emmy.

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Case Studies

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We have started to work with CBS News, bringing our ideas of character-driven storytelling to one of the most successful and biggest networks in the United States. Since beginning to work with them ratings have climbed and more importantly, audience engagement is through the ceiling.

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We started New York Times Television in 1990 and it was the first paper to be brought into the world of TV. It quickly became one of the most successful non-fiction production companies in the United States. The series and documentaries we produced won many awards including multiple Emmys.

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We have been working with the BBC since the year 2000 helping to convert their national news network to our visual storytelling technique. Most recently we have trained teams from their sports, documentaries, and comedy divisions to make character-driven stories using only smartphones.

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For the past five years we have worked with Spectrum News to introduce and train their journalists on visual, character driven storytelling using smartphones helping to create a different kind of local news for their network of 24-Hour News Stations across the United States.

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The United Nations

In 2006, we were approached by the United Nations. Rather than rely on news outlets, it would be much easier to train the field operatives to produce their own stories. We spent two years working with the UN, training more than 100 of their staff in bootcamps in Geneva and Nairobi.

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The Newark Star-Ledger

We trained 50 print reporters at the paper to shoot and tell their own stories, in conjunction with their print work. We built a TV newsroom in their existing print newsroom – you could not ask for a better set and they began to live stream their stories in conjunction with their print work.

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We spent two years with McGraw Hill, training more than 150 of their staffers, making them completely video literate. McGraw/Hill media properties we transit included Business Week, Aviation Week, (what was the name of the architecture magazine), and JD Power and Associates.

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Voice of America

In 1990, we were approached by The Voice of America, the official broadcasting agency for the United States Government. When we met with VOA, they were only a short wave radio broadcaster, but working with them, we took them into television, launching VOA-TV.

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Oyster Yachts

British based Oyster Yachts makes some of the finest yachts in the world. Like every other company, they had to find a way to feed the never-ending video demands of social media – sites like Instagram and TikTok. We trained the Oyster staff to tell their own stories, using only iPhones.

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Scottish Environmental Protection Agency

We were approached by SEPA, the Scottish Environmental Protection Agency because they had to continually find a way to ‘feed the media beast’. The result was that SEPA was able to tell their own stories, whenever they wanted, and at almost no additional cost.

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Michael on Media

Michael Rosenblum has been writing about the media since 1988. His work and ideas have appeared in The Guardian, The Huffington Post, Ilkeston Life and many other publications.

He has been blogging regularly for the past 35 years on this subject. Having taught media studies at Columbia University, NYU and now the University of Oxford, he is considered an expert on this subject.

Continue reading this post or look back at previous posts.

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