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 | man pages section 2: System Calls Oracle Solaris 11 Information Library |
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| man pages section 2: System Calls Oracle Solaris 11 Information Library |
- change the amount of space allocated for the calling process's data segment
#include <unistd.h>intbrk(void *endds);
void *sbrk(intptr_tincr);
Thebrk() andsbrk() functions are used to change dynamically the amountof space allocated for the calling process's data segment (seeexec(2)). Thechange is made by resetting the process's break value and allocating theappropriate amount of space. The break value is the address of the firstlocation beyond the end of the data segment. The amount of allocatedspace increases as the break value increases. Newly allocated space is setto zero. If, however, the same memory space is reallocated to thesame process its contents are undefined.
When a program begins execution usingexecve() the break is set atthe highest location defined by the program and data storage areas.
Thegetrlimit(2) function may be used to determine the maximum permissible size ofthedata segment; it is not possible to set the break beyondtherlim_max value returned from a call togetrlimit(), that is tosay, “end + rlim.rlim_max.” Seeend(3C).
Thebrk() function sets the break value toendds and changes theallocated space accordingly.
Thesbrk() function addsincr function bytes to the break valueand changes the allocated space accordingly. Theincr function can be negative, inwhich case the amount of allocated space is decreased.
Upon successful completion,brk() returns0. Otherwise, it returns-1 and setserrno to indicate the error.
Upon successful completion,sbrk() returns the prior break value. Otherwise, itreturns(void *)-1 and setserrno to indicate the error.
Thebrk() andsbrk() functions will fail and no additional memory willbe allocated if:
The data segment size limit as set bysetrlimit() (seegetrlimit(2)) would be exceeded; the maximum possible size of a data segment (compiled into the system) would be exceeded; insufficient space exists in the swap area to support the expansion; or the new break value would extend into an area of the address space defined by some previously established mapping (seemmap(2)).
Total amount of system memory available for private pages is temporarily insufficient. This may occur even though the space requested was less than the maximum data segment size (seeulimit(2)).
The behavior ofbrk() andsbrk() is unspecified if an application alsouses any other memory functions (such asmalloc(3C),mmap(2),free(3C)). Thebrk()andsbrk() functions have been used in specialized cases where no other memoryallocation function provided the same capability. The use ofmmap(2) isnow preferred because it can be used portably with all other memoryallocation functions and with any function that uses other allocation functions.
It is unspecified whether the pointer returned bysbrk() is aligned suitablyfor any purpose.
Seeattributes(5) for descriptions of the following attributes:
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exec(2),getrlimit(2),mmap(2),shmop(2),ulimit(2),end(3C),free(3C),malloc(3C)
The value ofincr may be adjusted by the system before settingthe new break value. Upon successful completion, the implementation guarantees aminimum ofincr bytes will be added to the data segment ifincris a positive value. Ifincr is a negative value, amaximum ofincr bytes will be removed from the data segment. Thisadjustment may not be necessary for all machine architectures.
The value of the arguments to bothbrk() andsbrk() are roundedup for alignment with eight-byte boundaries.
Setting the break may fail due to a temporary lack of swapspace. It is not possible to distinguish this from a failure causedby exceeding the maximum size of the data segment without consultinggetrlimit().
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