"QT" QT interprocess communication (shared memory) "Go"

Briefly

In the previous section, we shared how to use the Windows Messaging mechanism to communicate between different processes. But there are many limitations, such as: not cross-platform, and must be two processes exist at the same time, or process a sent the message who received it?

Let's share another way of communicating across platforms-shared memory (shared).

• Briefly
• Precautions
• Load into memory
  • Description
  • Realize
• Read from memory
  • Description
  • Realize

Precautions

When initializing the Qsharedmemory, a unique identity key must be specified, and the key of the process must remain consistent. You can use Setkey to set up.

Load into memory description

Process A-write

It is divided into the following steps:

1. Detects whether the process is connected to a shared memory segment and, if so, separates the process from the shared memory segment.
2. Get a new shared memory segment from the system's large enough memory.
3. Locks the shared memory segment to prevent the second dialog process from accessing and copying the picture in the buffer into the shared memory segment.
4. The shared memory segment is unlocked, and then the second dialog box process is accessible.

Realize

void Dialog::loadfromfile () {if (sharedmemory.isattached ()) {Detach the process from a shared memory segmentif (!sharedmemory.detach ()) Qdebug () <<"Unable to detach from shared memory."; } QString fileName = Qfiledialog::getopenfilename (0, QString (), QString (), TR ("Images (*.png *.xpm *.jpg)"); Qimage image;if (!image.load (FileName)) {qdebug () <<"Selected file is not a image, please select another.";Return }//load data into shared memory Qbuffer buffer; Buffer.open (qbuffer::readwrite); Qdatastream out (&buffer); out << image; int size = Buffer.size (); //Create shared Memory segment if (!sharedmemory.create (size)) {Qdebug () << Sharedmemory.errorstring () << return; } sharedmemory. lock (); char *to = (char*) Sharedmemory.data (); const char *from = Buffer.data (). Data (); memcpy (To, from, Qmin (Sharedmemory.size (), size)); Sharedmemory.unlock ();}   

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Read the description from memory

Process B-Read

It is divided into the following steps:

1. Bind the process to the shared memory segment created by process a
2. Locks the shared memory segment, copies the data to the buffer, and then writes to the Qimage.
3. Unlocks the shared memory segment, and then separates the process from the shared memory segment.

Realize

void MainWindow:: Loadfrommemory () {Binds shared memory to the processif (!sharedmemory. Attach ()) {Qdebug ()<<"Unable to attach to shared memory segment."; return;} //Read data from shared memory Qbuffer buffer; Qdatastream in (&buffer); Qimage image; SharedmemoryLock (); buffer. SetData ((char*) sharedmemory. Constdata (), Sharedmemory. Size ()); Buffer. Open (Qbuffer:: ReadOnly); in >> image; Sharedmemory. Unlock (); Sharedmemory. Detach (); M_plabel->setpixmap ( Qpixmap:: FromImage (image));}                

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"QT" QT interprocess communication (shared memory) "Go"