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The mutex class in the system. Threading namespace is used to control the connections between multiple threads without conflict or repetition. We can regard mutex as a taxi and passengers as a thread. The passenger first waits for the car, then gets on the bus, and finally gets off the bus. When a passenger is on the bus, other passengers can only get on the bus after they get off the bus. This is also the relationship between the thread and the mutex object. The thread uses mutex. the waitone

::weak_ptrThe strong reference type of the qsharedpointer has been very useful, why should there be a weak reference to the Qweakpointer?Qweakpointer is a smart pointer introduced to fit the Qsharedpointer, which is more like an assistant to Qsharedpointer (because it does not behave as a normal pointer, and does not overload operator* and). Its biggest role is to help qsharedpointer work, like a bystander to observe the use of resources. The weak_ptr is primarily designed to avoid strong r

memory, and if A is released, then B will cause the program to crash when it uses this memory.2. Understand the problem of assign in 1, then how to solve? The simplest method is to use a reference count (reference counting), or the above example, we set a reference count for that memory, and when the memory is assigned and assigned to a, the reference count is 1. The reference count increases to 2 when a is assigned to B. If a no longer uses this memory, it only needs to subtract the reference

permission statement, and we cannot determine who owns the permission. As a result, we need to correlate users and permissions in the application. It is common practice to assign permissions to a role and then associate the role with one or more users. Permission Declaration and granularity Shiro a permission declaration is usually a colon-delimited expression. As mentioned earlier, a permission expression can clearly specify the type of resource

linux. users have user names and user groups. Generally, users with the same name will be created at the same time. Log on to the root account to create a directory and a file. # Create a directory mkdir abc # Create a file touch abc.txt # View ls-all You will find: # Directory starting with d and file starting, and drwxr-xr-x 2 root 4096 Jun 6 abc-rw-r -- 1 root 0 Jun 6 abc.txt First look at the blue part above. The first part is the identifier. remove the first part and separate each thre

ownership, Hmutex momentarily becomes the excitation state, then wait ... The () function returns, at this time the state of the Hmutex is 被拥有 and 未激发 ;3, after ReleaseMutex, the state of Hmutex becomes 未被拥有 and 未激发 stateMutex considerations: The ownership of the mutex does not belong to which thread that produced it, but the last wait for this mutex ... () operation and a thread that has not yet been ReleaseMutex () operation. If the thread ow