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Hub AI
Shared library AI simulator
(@Shared library_simulator)
Hub AI
Shared library AI simulator
(@Shared library_simulator)
Shared library
A shared library is a library that contains executable code designed to be used by multiple computer programs or other libraries at runtime, with only one copy of that code in memory, shared by all programs using the code.
A library can be provided as static, dynamic, or both. A program that uses a static library is statically linked with the library; a program that uses a dynamic library is dynamically linked with the library. Historically, libraries could only be static. For static linking, code from the library is embedded into the program's executable file. A dynamically linked library is loaded at runtime from the library file.
A program requires a compiler and a linker step to access a library. In static linking, those references are fully resolved at compile time, whereas in dynamic linking, those references are not fully resolved until runtime by the operating system.
Many modern operating systems use a unified format for their dynamic libraries and executable files. For example:
This offers two main advantages: first, it requires only one loader (building and maintaining a single loader is considered well worth any added complexity). Secondly, it allows an executable file to be used as a shared library (if it has a symbol table).[citation needed]
Significant restrictions were placed on shared library code in some older environments, such as 16-bit Windows or MPE for the HP 3000, which only allowed stack-based (local) data.[citation needed]
Library code may be shared in memory by multiple processes and on disk. If virtual memory is used, processes would execute the same physical page of RAM mapped into the processes' different address spaces. This has advantages. For instance, on the OpenStep system, applications were often only a few hundred kilobytes in size and loaded quickly; most of their code was located in libraries already loaded for other purposes by the operating system.[citation needed]
Programs can accomplish RAM sharing by using position-independent code, as in Unix, which leads to a complex but flexible architecture, or by using common virtual addresses, as in Windows and OS/2. These systems ensure that code has a high probability of being shared by various means, like pre-mapping the address space and reserving slots for each shared library. A third alternative is a single-level store with a single address space, as used by the IBM System/38 and its successors. This allows position-dependent code, with programs and libraries assigned a permanent address in that address space.
Shared library
A shared library is a library that contains executable code designed to be used by multiple computer programs or other libraries at runtime, with only one copy of that code in memory, shared by all programs using the code.
A library can be provided as static, dynamic, or both. A program that uses a static library is statically linked with the library; a program that uses a dynamic library is dynamically linked with the library. Historically, libraries could only be static. For static linking, code from the library is embedded into the program's executable file. A dynamically linked library is loaded at runtime from the library file.
A program requires a compiler and a linker step to access a library. In static linking, those references are fully resolved at compile time, whereas in dynamic linking, those references are not fully resolved until runtime by the operating system.
Many modern operating systems use a unified format for their dynamic libraries and executable files. For example:
This offers two main advantages: first, it requires only one loader (building and maintaining a single loader is considered well worth any added complexity). Secondly, it allows an executable file to be used as a shared library (if it has a symbol table).[citation needed]
Significant restrictions were placed on shared library code in some older environments, such as 16-bit Windows or MPE for the HP 3000, which only allowed stack-based (local) data.[citation needed]
Library code may be shared in memory by multiple processes and on disk. If virtual memory is used, processes would execute the same physical page of RAM mapped into the processes' different address spaces. This has advantages. For instance, on the OpenStep system, applications were often only a few hundred kilobytes in size and loaded quickly; most of their code was located in libraries already loaded for other purposes by the operating system.[citation needed]
Programs can accomplish RAM sharing by using position-independent code, as in Unix, which leads to a complex but flexible architecture, or by using common virtual addresses, as in Windows and OS/2. These systems ensure that code has a high probability of being shared by various means, like pre-mapping the address space and reserving slots for each shared library. A third alternative is a single-level store with a single address space, as used by the IBM System/38 and its successors. This allows position-dependent code, with programs and libraries assigned a permanent address in that address space.