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Chapter 25
Process Management and Interprocess Communication
A process is an instance of a program. NSPR 2.0 provides routines to
create a new process and to wait for the termination of another process.
NSPR 2.0 does not provide an equivalent of the Unix fork(). The
newly-created process starts its execution from the beginning of its program.
A new process can inherit specified file descriptors from its parent,
and the parent can redirect the standard IO streams of the child process
to specified file descriptors.
Types and constants
#include <prinit.h>
typedef struct PRProcess PRProcess;
A process is identified by a pointer to the opaque PRProcess
structure.
typedef struct PRProcessAttr PRProcessAttr;
The attributes of a process to be created is described by the opaque
PRProcessAttr structure. A pointer to PRProcessAttr is
passed into PR_CreateProcess when a new process is created, specifying
information such as input/output redirection and file descriptor inheritance.
Functions
Specifying the attributes of a new process
When creating a process, one can use a PRProcessAttr structure
to specify the attributes of the new process.
PRProcessAttr *PR_NewProcessAttr(void);
PR_NewProcessAttr creates a new PRProcessAttr structure
and returns a pointer to it. The new PRProcessAttr structure is
initialized to the default attributes listed below:
-
The standard IO streams 0-2 (standard input, standard output, and standard
error) are not redirected
-
No file descriptors are inherited by the new process.
void PR_ResetProcessAttr(PRProcessAttr *attr);
PR_ResetProcessAttr initializes the PRProcessAttr
structure pointed to by attr to the default attributes. A PRProcessAttr
structure can be reused to create many new processes. Before creating a
different process, one has to re-initialize the PRProcessAttr
structure with a call to PR_ResetProcessAttr.
void PR_DestroyProcessAttr(PRProcessAttr *attr);
PR_DestroyProcessAttr destroys the PRProcessAttr structure
pointed to by attr. On return, the value of attr becomes
an invalid pointer and should not be passed to other functions.
void PR_SetStdioRedirect(PRProcessAttr *attr, PRInt32 stdioFd, PRFileDesc
*redirectFd);
The standard IO stream stdioFd (must be 0, 1, or 2) of the
new process will be redirected to the file descriptor redirectFd.
void PR_SetInheritableFileDesc(PRProcess *attr, PRFileDesc *fd,
const char *name);
The new process will inherit the file descriptor fd, which
is given the string name name. The new process can get the inherited
file descriptor by specifying the string name to PR_GetInheritedFileDesc.
Creating a new process
PRProcess *PR_CreateProcess(
const char *path,
char *const *argv,
char *const *envp,
const PRProcessAttr *attr
);
| path |
Pathname of the executable file. |
| argv |
A null-terminated array of character strings (the command-line arguments). |
| envp |
A null-terminated array of character strings (the environment strings).
Each string in the envp array is of the form:
name=value
envp can be NULL. |
| attr |
A pointer to a PRProcessAttr structure that describes the
attributes of the new process. attr can be NULL, which
means the new process will have the default attributes. |
PR_CreateProcess() creates a new process that executes the program
path, passing it the commmand-line arguments argv and
environment envp. If envp is NULL, the new process
inherits the environment of the parent process. The PRPRocessAttr
structure attr specifies the IO redirection and file descriptor
inheritance of the new process.
The newly-created process must be either detached (PR_DetachProcess)
or reaped (PR_WaitProcess), otherwise the memory for its PRProcess
structure is not reclaimed and results in memory leaks.
On success, PR_CreateProcess returns a pointer to a PRProcess
structure representing the new process. On failure, PR_CreateProcess
returns NULL. Call PR_GetError() to retrieve error information.
Detaching a child process
PRStatus PR_DetachProcess(PRProcess *process);
PR_DetachProcess detaches the specified process. A detached
process does not need to (and cannot) be reaped. On return, the value of
process becomes an invalid pointer and should not be passed to
other functions.
Waiting for a process to terminate
PRStatus PR_WaitProcess(PRProcess *process, PRInt32 *exitCode);
| process |
the identifier for the non-detached process whose termination we want
to wait for |
| exitCode |
a pointer to a PRInt32 variable for holding the
exit code of the process. Can be NULL. |
PR_WaitProcess() blocks the calling thread until the non-detached
process identified by process has terminated. On a successful
completion, PR_WaitProcess() returns PR_SUCCESS. If exitCode
is not NULL, *exitCode contains the exit status code
of process. On failure, PR_WaitProcess() returns PR_FAILURE.
Call PR_GetError() to retrieve error information.
Killing a process
PRStatus PR_KillProcess(PRProcess *process);
It is not clear whether this function is useful or it can be implemented
everywhere.
Obtaining inherited file descriptors
PRFileDesc * PR_GetInheritedFileDesc(const char *name);
The newly created process can use PR_GetInheritedFileDesc to
get the inherited file descriptor with the name name. The name
is given by its parent process. The parent and child must have some prearranged
agreement on the names of inherited file descriptors.
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Last updated: Wed Jul 15 09:52:17 PDT 1998
Copyright © 1998 Netscape
Communications Corporation
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