| 1 | $Id: Fork.os2 1281 2004-03-06 21:48:26Z bird $
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| 2 |
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| 3 | Fork Design Draft
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| 4 | --------------------
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| 5 |
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| 6 | 1.0 Intro
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| 7 | ----------
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| 8 |
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| 9 | blah.
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| 10 |
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| 11 |
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| 12 | 1.1 The SuS fork() Description
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| 13 | ------------------------------
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| 14 |
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| 15 | NAME
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| 16 |
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| 17 | fork - create a new process
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| 18 |
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| 19 | SYNOPSIS
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| 20 |
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| 21 | #include <unistd.h>
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| 22 |
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| 23 | pid_t fork(void);
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| 24 |
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| 25 | DESCRIPTION
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| 26 |
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| 27 | The fork() function shall create a new process. The new process (child process) shall be an exact copy of the calling process (parent process) except as detailed below:
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| 28 |
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| 29 | * The child process shall have a unique process ID.
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| 30 | * The child process ID also shall not match any active process
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| 31 | group ID.
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| 32 | * The child process shall have a different parent process ID,
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| 33 | which shall be the process ID of the calling process.
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| 34 | * The child process shall have its own copy of the parent's file
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| 35 | descriptors. Each of the child's file descriptors shall refer
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| 36 | to the same open file description with the corresponding file
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| 37 | descriptor of the parent.
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| 38 | * The child process shall have its own copy of the parent's open
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| 39 | directory streams. Each open directory stream in the child process
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| 40 | may share directory stream positioning with the corresponding
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| 41 | directory stream of the parent.
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| 42 | * [XSI] The child process shall have its own copy of the parent's
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| 43 | message catalog descriptors.
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| 44 | * The child process' values of tms_utime, tms_stime, tms_cutime, and
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| 45 | tms_cstime shall be set to 0.
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| 46 | * The time left until an alarm clock signal shall be reset to zero,
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| 47 | and the alarm, if any, shall be canceled; see alarm() .
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| 48 | * [XSI] All semadj values shall be cleared.
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| 49 | * File locks set by the parent process shall not be inherited by
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| 50 | the child process.
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| 51 | * The set of signals pending for the child process shall be
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| 52 | initialized to the empty set.
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| 53 | * [XSI] Interval timers shall be reset in the child process.
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| 54 | * [SEM] Any semaphores that are open in the parent process shall
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| 55 | also be open in the child process.
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| 56 | * [ML] The child process shall not inherit any address space memory
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| 57 | locks established by the parent process via calls to mlockall()
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| 58 | or mlock().
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| 59 | * [MF|SHM] Memory mappings created in the parent shall be retained
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| 60 | in the child process. MAP_PRIVATE mappings inherited from the
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| 61 | parent shall also be MAP_PRIVATE mappings in the child, and any
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| 62 | modifications to the data in these mappings made by the parent
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| 63 | prior to calling fork() shall be visible to the child. Any
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| 64 | modifications to the data in MAP_PRIVATE mappings made by the
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| 65 | parent after fork() returns shall be visible only to the parent.
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| 66 | Modifications to the data in MAP_PRIVATE mappings made by the
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| 67 | child shall be visible only to the child.
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| 68 | * [PS] For the SCHED_FIFO and SCHED_RR scheduling policies, the
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| 69 | child process shall inherit the policy and priority settings
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| 70 | of the parent process during a fork() function. For other s
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| 71 | cheduling policies, the policy and priority settings on fork()
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| 72 | are implementation-defined.
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| 73 | * [TMR] Per-process timers created by the parent shall not be
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| 74 | inherited by the child process.
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| 75 | * [MSG] The child process shall have its own copy of the message
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| 76 | queue descriptors of the parent. Each of the message descriptors
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| 77 | of the child shall refer to the same open message queue
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| 78 | description as the corresponding message descriptor of the parent.
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| 79 | * [AIO] No asynchronous input or asynchronous output operations
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| 80 | shall be inherited by the child process.
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| 81 | * A process shall be created with a single thread. If a
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| 82 | multi-threaded process calls fork(), the new process shall contain
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| 83 | a replica of the calling thread and its entire address space,
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| 84 | possibly including the states of mutexes and other resources.
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| 85 | Consequently, to avoid errors, the child process may only execute
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| 86 | async-signal-safe operations until such time as one of the exec
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| 87 | functions is called. [THR] Fork handlers may be established by
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| 88 | means of the pthread_atfork() function in order to maintain
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| 89 | application invariants across fork() calls.
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| 90 |
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| 91 | When the application calls fork() from a signal handler and any of
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| 92 | the fork handlers registered by pthread_atfork() calls a function
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| 93 | that is not asynch-signal-safe, the behavior is undefined.
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| 94 | * [TRC TRI] If the Trace option and the Trace Inherit option are
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| 95 | both supported:
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| 96 | If the calling process was being traced in a trace stream that
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| 97 | had its inheritance policy set to POSIX_TRACE_INHERITED, the
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| 98 | child process shall be traced into that trace stream, and the
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| 99 | child process shall inherit the parent's mapping of trace event
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| 100 | names to trace event type identifiers. If the trace stream in
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| 101 | which the calling process was being traced had its inheritance
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| 102 | policy set to POSIX_TRACE_CLOSE_FOR_CHILD, the child process
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| 103 | shall not be traced into that trace stream. The inheritance
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| 104 | policy is set by a call to the posix_trace_attr_setinherited()
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| 105 | function.
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| 106 | * [TRC] If the Trace option is supported, but the Trace Inherit
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| 107 | option is not supported:
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| 108 | The child process shall not be traced into any of the trace
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| 109 | streams of its parent process.
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| 110 | * [TRC] If the Trace option is supported, the child process of
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| 111 | a trace controller process shall not control the trace streams
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| 112 | controlled by its parent process.
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| 113 | * [CPT] The initial value of the CPU-time clock of the child
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| 114 | process shall be set to zero.
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| 115 | * [TCT] The initial value of the CPU-time clock of the single
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| 116 | thread of the child process shall be set to zero.
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| 117 |
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| 118 | All other process characteristics defined by IEEE Std 1003.1-2001 shall
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| 119 | be the same in the parent and child processes. The inheritance of
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| 120 | process characteristics not defined by IEEE Std 1003.1-2001 is
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| 121 | unspecified by IEEE Std 1003.1-2001.
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| 122 |
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| 123 | After fork(), both the parent and the child processes shall be capable
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| 124 | of executing independently before either one terminates.
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| 125 |
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| 126 | RETURN VALUE
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| 127 |
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| 128 | Upon successful completion, fork() shall return 0 to the child process
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| 129 | and shall return the process ID of the child process to the parent
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| 130 | process. Both processes shall continue to execute from the fork()
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| 131 | function. Otherwise, -1 shall be returned to the parent process, no
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| 132 | child process shall be created, and errno shall be set to indicate
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| 133 | the error.
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| 134 |
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| 135 | ERRORS
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| 136 |
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| 137 | The fork() function shall fail if:
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| 138 |
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| 139 | [EAGAIN]
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| 140 | The system lacked the necessary resources to create another
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| 141 | process, or the system-imposed limit on the total number of
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| 142 | processes under execution system-wide or by a single user
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| 143 | {CHILD_MAX} would be exceeded.
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| 144 |
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| 145 | The fork() function may fail if:
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| 146 |
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| 147 | [ENOMEM]
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| 148 | Insufficient storage space is available.
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| 149 |
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| 150 |
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| 151 |
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| 152 |
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| 153 | 2.0 Requirements and Assumptions Of The Implementation
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| 154 | ------------------------------------------------------
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| 155 |
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