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CodeSOD: A Single Lint Problem

The Daily WTF
4 months 3 weeks ago

We've discussed singleton abuse as an antipattern many times on this site, but folks keep trying to find new ways to implement them badly. And Olivia's co-worker certainly found one.

We start with a C++ utility class with a bunch of functions in it:

//utilities.h class CUtilities { public CUtilities(); void doSomething(); void doSomeOtherThing(); }; extern CUtilities* g_Utility;

So yes, if you're making a pile of utility methods, or if you want a singleton object, the keyword you're looking for is static. We'll set that aside. This class declares a class, and then also declares that there will be a pointer to the class, somewhere.

We don't have to look far.

//utilities.cpp CUtilities* g_Utility = nullptr; CUtilities::CUtilities() { g_Utility = this; } // all my do-whatever functions here

This defines the global pointer variable, and then also writes the constructor of the utility class so that it initializes the global pointer to itself.

It's worth noting, at this point, that this is not a singleton, because this does nothing to prevent multiple instances from being created. What it does guarantee is that for each new instance, we overwrite g_Utility without disposing of what was already in there, which is a nice memory leak.

But where, or where, does the constructor get called?

//startup.h class CUtilityInit { private: CUtilities m_Instance; }; //startup.cpp CUtilityInit *utils = new CUtilityInit();

I don't hate a program that starts with an initialization step that clearly instantiates all the key objects. There's just one little problem here that we'll come back to in just a moment, but let's look at the end result.

Anywhere that needs the utilities now can do this:

#include "utilities.h" //in the code g_Utility->doSomething();

There's just one key problem: back in the startup.h, we have a private member called CUtilities m_Instance which is never referenced anywhere else in the code. This means when people, like Olivia, are trawling through the codebase looking for linter errors they can fix, they may see an "unused member" and decide to remove it. Which is what Olivia did.

The result compiles just fine, but explodes at runtime since g_Utility was never initialized.

The fix was simple: just don't try and make this a singleton, since it isn't one anyway. At startup, she just populated g_Utility with an instance, and threw away all the weird code around populating it through construction.

Singletons are, as a general rule, bad. Badly implemented singletons themselves easily turn into landmines waiting for unwary developers. Stop being clever and don't try and apply a design pattern for the sake of saying you used a design pattern.

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Remy Porter

China says its lunar lander passed Luna-landing and take-off tests

The Register
4 months 3 weeks ago
Current plan calls for Taikonaut touchdown around 2030

China’s Manned Space Engineering Network says the country’s first crewed lunar lander last week completed a comprehensive landing and takeoff verification test, bringing it closer to landing on Luna - and leaving it again afterwards.…

Simon Sharwood

How 12 'Enola Gay' Crew Members Remember Dropping the Atomic Bomb

Slashdot
4 months 3 weeks ago
Last week saw the 80th anniversary of a turning point in World War II: the day America dropped an atomic bomb on Hiroshima. "Twelve men were on that flight..." remembers the online magazine Mental Floss, adding "Almost all had something to say after the war." The group was segregated from the rest of the military and trained in secret. Even those in the group only knew as much as they needed to know in order to perform their duties. The group deployed to Tinian in 1945 with 15 B-29 bombers, flight crews, ground crews, and other personnel, a total of about 1770 men. The mission to drop the atomic bomb on Hiroshima, Japan (special mission 13) involved seven planes, but the one we remember was the Enola Gay. Air Force captain Theodore "Dutch" Van Kirk did not know the destructive force of the nuclear bomb before Hiroshima. He was 24 years old at that time, a veteran of 58 missions in North Africa. Paul Tibbets told him this mission would shorten or end the war, but Van Kirk had heard that line before. Hiroshima made him a believer. Van Kirk felt the bombing of Hiroshima was worth the price in that it ended the war before the invasion of Japan, which promised to be devastating to both sides. " I honestly believe the use of the atomic bomb saved lives in the long run. There were a lot of lives saved. Most of the lives saved were Japanese." In 2005, Van Kirk came as close as he ever got to regret. "I pray no man will have to witness that sight again. Such a terrible waste, such a loss of life..." Many of the other crewmembers also felt the bomb ultimately saved lives. The Washington Post has also published a new oral history of the flight after it took off from Tinian Island. The oral history was assembled for a new book published this week titled The Devil Reached Toward the Sky: An Oral History of the Making and Unleashing of the Atomic Bomb.. Col. Paul W. Tibbets, lead pilot of the Enola Gay: We were only eight minutes off the ground when Capt. William S. "Deak" Parsons and Lt. Morris R. Jeppson lowered themselves into the bomb bay to insert a slug of uranium and the conventional explosive charge into the core of the strange-looking weapon. I wondered why we were calling it ''Little Boy." Little Boy was 28 inches in diameter and 12 feet long. Its weight was a little more than 9,000 pounds. With its coat of dull gunmetal paint, it was an ugly monster... Lt. Morris R. Jeppson, crew member of the Enola Gay: Parsons was second-in-command of the military in the Manhattan Project. The Little Boy weapon was Parsons's design. He was greatly concerned that B-29s loaded with conventional bombs were crashing at the ends of runways on Tinian during takeoff and that such an event could cause the U-235 projectile in the gun of Little Boy to fly down the barrel and into the U-235 target. This could have caused a low-level nuclear explosion on Tinian... Jeppson: On his own, Parsons decided that he would go on the Hiroshima mission and that he would load the gun after the Enola Gay was well away from Tinian. Tibbets: That way, if we crashed, we would lose only the airplane and crew, himself included... Jeppson held the flashlight while Parsons struggled with the mechanism of the bomb, inserting the explosive charge that would send one block of uranium flying into the other to set off the instant chain reaction that would create the atomic explosion. The navigator on one of the other six planes on the mission remember that watching the mushroom cloud, "There was almost complete silence on the flight deck. It was evident the city of Hiroshima was destroyed." And the Enola Gay's copilot later remembered thinking: "My God, what have we done?"

Read more of this story at Slashdot.

EditorDavid