Shared libraries implemented with linking program loader

In a computer system comprising an electronic digital computer including a central processing unit, a computer memory and a disk storage unit, and computer software including at least two computer programs for operating said computer, a method for utilizing a library in said two or more computer programs, comprising the steps of:

• said computer system maintaining in said computer memory a library, including library items and a library symbol table, said library items including executable library routines, each entry in the library symbol table containing a symbol that represents one of the library items and an address of said one of the library items;
• said computer system, in response to a first computer program being invoked by a user for execution, loading from said disk storage unit into said computer memory a first relocatable file representing the first computer program, said first relocatable file including program code having one or more symbols, each of which references one of said library routines;
• said computer system, after the first relocatable file is loaded into said computer memory, finding in the library symbol table addresses of library routines that are referenced by symbols in the program code of the first computer program;
• said computer system inserting the addresses of the referenced library routines into the program code of the first relocatable file in said computer memory such that the first computer program is ready for execution;
• said computer system, in response to a second computer program being invoked by a user for execution, loading from said disk storage unit into said computer memory a second relocatable file representing the second computer program, said second relocatable file including program code having one or more symbols, each of which references one of said library routines;
• said computer system, after the second relocatable file is loaded into said computer memory, finding in the library symbol table addresses of library routines that are referenced by symbols in the program code of the second computer program;
• and
• said computer system inserting the addresses of the referenced library routines into the program code of the second relocatable file in said computer memory such that the second computer program is ready for execution and such that said executable library routines remain unmodified during execution of the first computer program and the second computer program so that only one copy of the executable library routines is required in said computer memory, said relocatable files each including an unsorted program symbol table containing symbols and corresponding indices that represent library routines referenced by the program code and further including relocation information containing program locations in the program code of references to library routines and indices of corresponding symbols in the unsorted program symbol table, wherein the steps of finding addresses of library routines each includes the steps of finding in the library symbol table symbols that appear in the unsorted program symbol table, each of said symbols having an address of a library routine listed therewith in the library symbol table, and writing the addresses of the library routines corresponding to said symbols in the unsorted program symbol table and wherein the steps of inserting the addresses of referenced library routines into the program code each includes the steps of accessing each program location contained in the relocation information, using the indices in the relocation information to find the corresponding address of a referenced library routine in the unsorted program symbol table and writing the corresponding address of the referenced library routine contained in the unsorted program symbol table in the accessed program location.