[Deadlock Sub Download
Jamar Lizarraga
2) Deadlock detection and recovery: If Deadlock prevention or avoidance is not applied to the software then we can handle this by deadlock detection and recovery. which consist of two phases:
In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lock.[1] Deadlocks are a common problem in multiprocessing systems, parallel computing, and distributed systems, because in these contexts systems often use software or hardware locks to arbitrate shared resources and implement process synchronization.[2]
In an operating system, a deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process.[3] If a process remains indefinitely unable to change its state because resources requested by it are being used by another process that itself is waiting, then the system is said to be in a deadlock.[4]
Most current operating systems cannot prevent deadlocks.[11] When a deadlock occurs, different operating systems respond to them in different non-standard manners. Most approaches work by preventing one of the four Coffman conditions from occurring, especially the fourth one.[12] Major approaches are as follows.
In this approach, it is assumed that a deadlock will never occur. This is also an application of the Ostrich algorithm.[12][13] This approach was initially used by MINIX and UNIX.[9] This is used when the time intervals between occurrences of deadlocks are large and the data loss incurred each time is tolerable.
Under the deadlock detection, deadlocks are allowed to occur. Then the state of the system is examined to detect that a deadlock has occurred and subsequently it is corrected. An algorithm is employed that tracks resource allocation and process states, it rolls back and restarts one or more of the processes in order to remove the detected deadlock. Detecting a deadlock that has already occurred is easily possible since the resources that each process has locked and/or currently requested are known to the resource scheduler of the operating system.[13]
Similar to deadlock prevention, deadlock avoidance approach ensures that deadlock will not occur in a system. The term "deadlock avoidance" appears to be very close to "deadlock prevention" in a linguistic context, but they are very much different in the context of deadlock handling. Deadlock avoidance does not impose any conditions as seen in prevention but, here each resource request is carefully analyzed to see whether it could be safely fulfilled without causing deadlock.
Deadlock avoidance requires that the operating system be given in advance additional information concerning which resources a process will request and use during its lifetime. Deadlock avoidance algorithm analyzes each and every request by examining that there is no possibility of deadlock occurrence in the future if the requested resource is allocated. The drawback of this approach is its requirement of information in advance about how resources are to be requested in the future. One of the most used deadlock avoidance algorithms is Banker's algorithm.[17]
The term was coined by Edward A. Ashcroft in a 1975 paper[18] in connection with an examination of airline booking systems.[19] Livelock is a special case of resource starvation; the general definition only states that a specific process is not progressing.[20]
Livelock is a risk with some algorithms that detect and recover from deadlock. If more than one process takes action, the deadlock detection algorithm can be repeatedly triggered. This can be avoided by ensuring that only one process (chosen arbitrarily or by priority) takes action.[21]
One option to resolve this deadlock is for the international community, and the United States and Europe in particular, to impose an end to the occupation and facilitate the two-state settlement they claim to endorse.
"dispatch_sync": "Submits a block to a dispatch queue for synchronous execution. Unlike dispatch_async, this function does not return until the block has finished. Calling this function and targeting the current queue results in deadlock.".
If you dispatch_sync to myQueue like that and the call happens on the main thread, then dispatch_sync will, if possible, execute the block right there and not on a new worker thread like dispatch_async would. You're not guaranteed to get a separate worker thread for your queue.
The block then runs on the main thread until it hits your second dispatch_sync call, which happens to target the main queue. That queue can't be serviced, since there's already a block running on it, and that's where you end up in a deadlock.
If that's your problem, i.e. the first dispatch_sync is indeed coming from the main thread, then you should switch to dispatch_async. You wouldn't want to block the main thread with the long-running "EXTREME PROCESSING" operation.
You are calling dispatch_sync twice. The first time suspends the main thread waiting for your block to complete. The block then suspends the background thread with the second call which tries to push back to the main thread (which will never process the block from its queue because it's suspended). Both threads are now waiting for each other.
Read my Geodatabase Connections Best Practices Article in the link below, it talks about deadlocks and how to resolve the problem.
Mapping and Charting Solutions (MCS) Enterprise Da... - Esri Community
Powering with the STLK jumper is fine, the trick at least with the H747-DISCO was to completely disconnect the board from ALL power sources, and connect/disconnect the sole cable several times, with the BOOT0 pads solder bridged to VCC
The H7 has a weird reset methodology the NRST is not the same as the Power-On-Reset, which recovers settings/options from flash, as part of some security mechanism and starting thru ROM. If the Flash is not blank, it then transfers control.
Your code is perhaps executing, I think that putting some break-out/erase code to check a GPIO pin prior to the SMPS/LDO and VOS settings might permit simpler recovery. I'd probably use the BLUE USER button to nuke the device during future development.
Thx clive1; so I did change the power supply to the USB adapter (did power with the ST Link before). Therefore I could keep the ST-Link attached and did cycle the power while Boot0 was high (SW1 in SysMem position). Howerver I could not establish a connection to get to erase the flash. What could I possibly miss? I had no problems to recover my STM32F4s in the past...
Yes, ST has been advised to improve how the recovery of this type of situation is handled. I had an early 747I and bricked the board very quickly. The unresponsiveness of the device was very disconcerting.
Thanks @Tesla DeLorean . Works like a breeze even for H735 discovery board. Apparently this deadlock happens if power settings in firmware are different from that of hardware. This issue is most likely to occur when programming the discovery board for the first time. The board gets detected, user flashes some program (with incorrect power settings in the firmware, without noticing), it works, but cannot connect it to STLink from the next time. Just follow section 6.2.4 in UM (for H735 disc)
You need to unndertand the AStar module. The taskexecuter travel from a grid point to another. If several taskexecuters occupy conjunction grid points and must travel through each other you get into a deadlock. In other words, there are not enough grid points the taskexecuters can acquire to pass each other. Please set the grid points to visible in your model. You get into the properties by the border frame of the AStar area.
You can tell that the locks aren't reentrant because they give mutable access to the contents. A reentrant lock can only give immutable access (but the contents may be Send + !Sync so they can contain a Cell or RefCell)
It's probably worth pointing out that deadlock detection of async locks is fundamentally impossible because locking the mutex in both branches of a tokio::join! is indistinguishable from your code, but if they are in separate branches of a tokio::join!, then its not necessarily a deadlock.
We're going to build up a deadlock together. If you're unfamiliar with Rust and/or its multithreaded concepts, you'll probably learn a lot from this. If you are familiar with Rust's multithreading capabilities, my guess is you'll be as surprised by this deadlock as I was. And if you spot the deadlock immediately, you get a figurative hat-tip from me.
As to the title, this deadlock was the worst I ever experienced because of how subtle it was. It was the best because of the tooling told me exactly where the problem was. You'll see both points come out below.
So we'll do something very similar here! I'm going to simulate some kind of an access control program that allows multiple threads to use some shared, mutable state representing a person. And we'll make two sets of accesses to this state:
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